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pigweed / third_party / github / abseil / abseil-cpp / 60b5e1f2c07e545d471a326eb7979ba518c73652 / . / absl / container / internal / raw_hash_set.h
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// Copyright 2018 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// An open-addressing
// hashtable with quadratic probing.
//
// This is a low level hashtable on top of which different interfaces can be
// implemented, like flat_hash_set, node_hash_set, string_hash_set, etc.
//
// The table interface is similar to that of std::unordered_set. Notable
// differences are that most member functions support heterogeneous keys when
// BOTH the hash and eq functions are marked as transparent. They do so by
// providing a typedef called `is_transparent`.
//
// When heterogeneous lookup is enabled, functions that take key_type act as if
// they have an overload set like:
//
// iterator find(const key_type& key);
// template <class K>
// iterator find(const K& key);
//
// size_type erase(const key_type& key);
// template <class K>
// size_type erase(const K& key);
//
// std::pair<iterator, iterator> equal_range(const key_type& key);
// template <class K>
// std::pair<iterator, iterator> equal_range(const K& key);
//
// When heterogeneous lookup is disabled, only the explicit `key_type` overloads
// exist.
//
// In addition the pointer to element and iterator stability guarantees are
// weaker: all iterators and pointers are invalidated after a new element is
// inserted.
//
// IMPLEMENTATION DETAILS
//
// # Table Layout
//
// A raw_hash_set's backing array consists of control bytes followed by slots
// that may or may not contain objects.
//
// The layout of the backing array, for `capacity` slots, is thus, as a
// pseudo-struct:
//
// struct BackingArray {
// // Sampling handler. This field isn't present when the sampling is
// // disabled or this allocation hasn't been selected for sampling.
// HashtablezInfoHandle infoz_;
// // The number of elements we can insert before growing the capacity.
// size_t growth_left;
// // Control bytes for the "real" slots.
// ctrl_t ctrl[capacity];
// // Always `ctrl_t::kSentinel`. This is used by iterators to find when to
// // stop and serves no other purpose.
// ctrl_t sentinel;
// // A copy of the first `kWidth - 1` elements of `ctrl`. This is used so
// // that if a probe sequence picks a value near the end of `ctrl`,
// // `Group` will have valid control bytes to look at.
// ctrl_t clones[kWidth - 1];
// // The actual slot data.
// slot_type slots[capacity];
// };
//
// The length of this array is computed by `RawHashSetLayout::alloc_size` below.
//
// Control bytes (`ctrl_t`) are bytes (collected into groups of a
// platform-specific size) that define the state of the corresponding slot in
// the slot array. Group manipulation is tightly optimized to be as efficient
// as possible: SSE and friends on x86, clever bit operations on other arches.
//
// Group 1 Group 2 Group 3
// +---------------+---------------+---------------+
// | | | | | | | | | | | | | | | | | | | | | | | | |
// +---------------+---------------+---------------+
//
// Each control byte is either a special value for empty slots, deleted slots
// (sometimes called *tombstones*), and a special end-of-table marker used by
// iterators, or, if occupied, seven bits (H2) from the hash of the value in the
// corresponding slot.
//
// Storing control bytes in a separate array also has beneficial cache effects,
// since more logical slots will fit into a cache line.
//
// # Small Object Optimization (SOO)
//
// When the size/alignment of the value_type and the capacity of the table are
// small, we enable small object optimization and store the values inline in
// the raw_hash_set object. This optimization allows us to avoid
// allocation/deallocation as well as cache/dTLB misses.
//
// # Hashing
//
// We compute two separate hashes, `H1` and `H2`, from the hash of an object.
// `H1(hash(x))` is an index into `slots`, and essentially the starting point
// for the probe sequence. `H2(hash(x))` is a 7-bit value used to filter out
// objects that cannot possibly be the one we are looking for.
//
// # Table operations.
//
// The key operations are `insert`, `find`, and `erase`.
//
// Since `insert` and `erase` are implemented in terms of `find`, we describe
// `find` first. To `find` a value `x`, we compute `hash(x)`. From
// `H1(hash(x))` and the capacity, we construct a `probe_seq` that visits every
// group of slots in some interesting order.
//
// We now walk through these indices. At each index, we select the entire group
// starting with that index and extract potential candidates: occupied slots
// with a control byte equal to `H2(hash(x))`. If we find an empty slot in the
// group, we stop and return an error. Each candidate slot `y` is compared with
// `x`; if `x == y`, we are done and return `&y`; otherwise we continue to the
// next probe index. Tombstones effectively behave like full slots that never
// match the value we're looking for.
//
// The `H2` bits ensure when we compare a slot to an object with `==`, we are
// likely to have actually found the object. That is, the chance is low that
// `==` is called and returns `false`. Thus, when we search for an object, we
// are unlikely to call `==` many times. This likelyhood can be analyzed as
// follows (assuming that H2 is a random enough hash function).
//
// Let's assume that there are `k` "wrong" objects that must be examined in a
// probe sequence. For example, when doing a `find` on an object that is in the
// table, `k` is the number of objects between the start of the probe sequence
// and the final found object (not including the final found object). The
// expected number of objects with an H2 match is then `k/128`. Measurements
// and analysis indicate that even at high load factors, `k` is less than 32,
// meaning that the number of "false positive" comparisons we must perform is
// less than 1/8 per `find`.
// `insert` is implemented in terms of `unchecked_insert`, which inserts a
// value presumed to not be in the table (violating this requirement will cause
// the table to behave erratically). Given `x` and its hash `hash(x)`, to insert
// it, we construct a `probe_seq` once again, and use it to find the first
// group with an unoccupied (empty *or* deleted) slot. We place `x` into the
// first such slot in the group and mark it as full with `x`'s H2.
//
// To `insert`, we compose `unchecked_insert` with `find`. We compute `h(x)` and
// perform a `find` to see if it's already present; if it is, we're done. If
// it's not, we may decide the table is getting overcrowded (i.e. the load
// factor is greater than 7/8 for big tables; `is_small()` tables use a max load
// factor of 1); in this case, we allocate a bigger array, `unchecked_insert`
// each element of the table into the new array (we know that no insertion here
// will insert an already-present value), and discard the old backing array. At
// this point, we may `unchecked_insert` the value `x`.
//
// Below, `unchecked_insert` is partly implemented by `prepare_insert`, which
// presents a viable, initialized slot pointee to the caller.
//
// `erase` is implemented in terms of `erase_at`, which takes an index to a
// slot. Given an offset, we simply create a tombstone and destroy its contents.
// If we can prove that the slot would not appear in a probe sequence, we can
// make the slot as empty, instead. We can prove this by observing that if a
// group has any empty slots, it has never been full (assuming we never create
// an empty slot in a group with no empties, which this heuristic guarantees we
// never do) and find would stop at this group anyways (since it does not probe
// beyond groups with empties).
//
// `erase` is `erase_at` composed with `find`: if we
// have a value `x`, we can perform a `find`, and then `erase_at` the resulting
// slot.
//
// To iterate, we simply traverse the array, skipping empty and deleted slots
// and stopping when we hit a `kSentinel`.
#ifndef ABSL_CONTAINER_INTERNAL_RAW_HASH_SET_H_
#define ABSL_CONTAINER_INTERNAL_RAW_HASH_SET_H_
#include <algorithm>
#include <cassert>
#include <cmath>
#include <cstddef>
#include <cstdint>
#include <cstring>
#include <functional>
#include <initializer_list>
#include <iterator>
#include <limits>
#include <memory>
#include <tuple>
#include <type_traits>
#include <utility>
#include "absl/base/attributes.h"
#include "absl/base/config.h"
#include "absl/base/internal/endian.h"
#include "absl/base/internal/iterator_traits.h"
#include "absl/base/internal/raw_logging.h"
#include "absl/base/macros.h"
#include "absl/base/optimization.h"
#include "absl/base/options.h"
#include "absl/base/port.h"
#include "absl/base/prefetch.h"
#include "absl/container/internal/common.h" // IWYU pragma: export // for node_handle
#include "absl/container/internal/common_policy_traits.h"
#include "absl/container/internal/compressed_tuple.h"
#include "absl/container/internal/container_memory.h"
#include "absl/container/internal/hash_function_defaults.h"
#include "absl/container/internal/hash_policy_traits.h"
#include "absl/container/internal/hashtable_control_bytes.h"
#include "absl/container/internal/hashtable_debug_hooks.h"
#include "absl/container/internal/hashtablez_sampler.h"
#include "absl/functional/function_ref.h"
#include "absl/hash/hash.h"
#include "absl/memory/memory.h"
#include "absl/meta/type_traits.h"
#include "absl/numeric/bits.h"
#include "absl/utility/utility.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace container_internal {
#ifdef ABSL_SWISSTABLE_ENABLE_GENERATIONS
#error ABSL_SWISSTABLE_ENABLE_GENERATIONS cannot be directly set
#elif (defined(ABSL_HAVE_ADDRESS_SANITIZER) || \
defined(ABSL_HAVE_HWADDRESS_SANITIZER) || \
defined(ABSL_HAVE_MEMORY_SANITIZER)) && \
!defined(NDEBUG_SANITIZER) // If defined, performance is important.
// When compiled in sanitizer mode, we add generation integers to the backing
// array and iterators. In the backing array, we store the generation between
// the control bytes and the slots. When iterators are dereferenced, we assert
// that the container has not been mutated in a way that could cause iterator
// invalidation since the iterator was initialized.
#define ABSL_SWISSTABLE_ENABLE_GENERATIONS
#endif
#ifdef ABSL_SWISSTABLE_ASSERT
#error ABSL_SWISSTABLE_ASSERT cannot be directly set
#else
// We use this macro for assertions that users may see when the table is in an
// invalid state that sanitizers may help diagnose.
#define ABSL_SWISSTABLE_ASSERT(CONDITION) \
assert((CONDITION) && "Try enabling sanitizers.")
#endif
// We use uint8_t so we don't need to worry about padding.
using GenerationType = uint8_t;
// A sentinel value for empty generations. Using 0 makes it easy to constexpr
// initialize an array of this value.
constexpr GenerationType SentinelEmptyGeneration() { return 0; }
constexpr GenerationType NextGeneration(GenerationType generation) {
return ++generation == SentinelEmptyGeneration() ? ++generation : generation;
}
#ifdef ABSL_SWISSTABLE_ENABLE_GENERATIONS
constexpr bool SwisstableGenerationsEnabled() { return true; }
constexpr size_t NumGenerationBytes() { return sizeof(GenerationType); }
#else
constexpr bool SwisstableGenerationsEnabled() { return false; }
constexpr size_t NumGenerationBytes() { return 0; }
#endif
// Returns true if we should assert that the table is not accessed after it has
// been destroyed or during the destruction of the table.
constexpr bool SwisstableAssertAccessToDestroyedTable() {
#ifndef NDEBUG
return true;
#endif
return SwisstableGenerationsEnabled();
}
template <typename AllocType>
void SwapAlloc(AllocType& lhs, AllocType& rhs,
std::true_type /* propagate_on_container_swap */) {
using std::swap;
swap(lhs, rhs);
}
template <typename AllocType>
void SwapAlloc(AllocType& lhs, AllocType& rhs,
std::false_type /* propagate_on_container_swap */) {
(void)lhs;
(void)rhs;
assert(lhs == rhs &&
"It's UB to call swap with unequal non-propagating allocators.");
}
template <typename AllocType>
void CopyAlloc(AllocType& lhs, AllocType& rhs,
std::true_type /* propagate_alloc */) {
lhs = rhs;
}
template <typename AllocType>
void CopyAlloc(AllocType&, AllocType&, std::false_type /* propagate_alloc */) {}
// The state for a probe sequence.
//
// Currently, the sequence is a triangular progression of the form
//
// p(i) := Width * (i^2 + i)/2 + hash (mod mask + 1)
//
// The use of `Width` ensures that each probe step does not overlap groups;
// the sequence effectively outputs the addresses of *groups* (although not
// necessarily aligned to any boundary). The `Group` machinery allows us
// to check an entire group with minimal branching.
//
// Wrapping around at `mask + 1` is important, but not for the obvious reason.
// As described above, the first few entries of the control byte array
// are mirrored at the end of the array, which `Group` will find and use
// for selecting candidates. However, when those candidates' slots are
// actually inspected, there are no corresponding slots for the cloned bytes,
// so we need to make sure we've treated those offsets as "wrapping around".
//
// It turns out that this probe sequence visits every group exactly once if the
// number of groups is a power of two, since (i^2+i)/2 is a bijection in
// Z/(2^m). See https://en.wikipedia.org/wiki/Quadratic_probing
template <size_t Width>
class probe_seq {
public:
// Creates a new probe sequence using `hash` as the initial value of the
// sequence and `mask` (usually the capacity of the table) as the mask to
// apply to each value in the progression.
probe_seq(size_t hash, size_t mask) {
ABSL_SWISSTABLE_ASSERT(((mask + 1) & mask) == 0 && "not a mask");
mask_ = mask;
offset_ = hash & mask_;
}
// The offset within the table, i.e., the value `p(i)` above.
size_t offset() const { return offset_; }
size_t offset(size_t i) const { return (offset_ + i) & mask_; }
void next() {
index_ += Width;
offset_ += index_;
offset_ &= mask_;
}
// 0-based probe index, a multiple of `Width`.
size_t index() const { return index_; }
private:
size_t mask_;
size_t offset_;
size_t index_ = 0;
};
template <class ContainerKey, class Hash, class Eq>
struct RequireUsableKey {
template <class PassedKey, class... Args>
std::pair<
decltype(std::declval<const Hash&>()(std::declval<const PassedKey&>())),
decltype(std::declval<const Eq&>()(std::declval<const ContainerKey&>(),
std::declval<const PassedKey&>()))>*
operator()(const PassedKey&, const Args&...) const;
};
template <class E, class Policy, class Hash, class Eq, class... Ts>
struct IsDecomposable : std::false_type {};
template <class Policy, class Hash, class Eq, class... Ts>
struct IsDecomposable<
absl::void_t<decltype(Policy::apply(
RequireUsableKey<typename Policy::key_type, Hash, Eq>(),
std::declval<Ts>()...))>,
Policy, Hash, Eq, Ts...> : std::true_type {};
// TODO(alkis): Switch to std::is_nothrow_swappable when gcc/clang supports it.
template <class T>
constexpr bool IsNoThrowSwappable(std::true_type = {} /* is_swappable */) {
using std::swap;
return noexcept(swap(std::declval<T&>(), std::declval<T&>()));
}
template <class T>
constexpr bool IsNoThrowSwappable(std::false_type /* is_swappable */) {
return false;
}
// See definition comment for why this is size 32.
ABSL_DLL extern const ctrl_t kEmptyGroup[32];
// We use these sentinel capacity values in debug mode to indicate different
// classes of bugs.
enum InvalidCapacity : size_t {
kAboveMaxValidCapacity = ~size_t{} - 100,
kReentrance,
kDestroyed,
// These two must be last because we use `>= kMovedFrom` to mean moved-from.
kMovedFrom,
kSelfMovedFrom,
};
// Returns a pointer to a control byte group that can be used by empty tables.
inline ctrl_t* EmptyGroup() {
// Const must be cast away here; no uses of this function will actually write
// to it because it is only used for empty tables.
return const_cast<ctrl_t*>(kEmptyGroup + 16);
}
// For use in SOO iterators.
// TODO(b/289225379): we could potentially get rid of this by adding an is_soo
// bit in iterators. This would add branches but reduce cache misses.
ABSL_DLL extern const ctrl_t kSooControl[17];
// Returns a pointer to a full byte followed by a sentinel byte.
inline ctrl_t* SooControl() {
// Const must be cast away here; no uses of this function will actually write
// to it because it is only used for SOO iterators.
return const_cast<ctrl_t*>(kSooControl);
}
// Whether ctrl is from the SooControl array.
inline bool IsSooControl(const ctrl_t* ctrl) { return ctrl == SooControl(); }
// Returns a pointer to a generation to use for an empty hashtable.
GenerationType* EmptyGeneration();
// Returns whether `generation` is a generation for an empty hashtable that
// could be returned by EmptyGeneration().
inline bool IsEmptyGeneration(const GenerationType* generation) {
return *generation == SentinelEmptyGeneration();
}
// We only allow a maximum of 1 SOO element, which makes the implementation
// much simpler. Complications with multiple SOO elements include:
// - Satisfying the guarantee that erasing one element doesn't invalidate
// iterators to other elements means we would probably need actual SOO
// control bytes.
// - In order to prevent user code from depending on iteration order for small
// tables, we would need to randomize the iteration order somehow.
constexpr size_t SooCapacity() { return 1; }
// Sentinel type to indicate SOO CommonFields construction.
struct soo_tag_t {};
// Sentinel type to indicate SOO CommonFields construction with full size.
struct full_soo_tag_t {};
// Sentinel type to indicate non-SOO CommonFields construction.
struct non_soo_tag_t {};
// Sentinel value to indicate an uninitialized value explicitly.
struct uninitialized_tag_t {};
// Sentinel value to indicate creation of an empty table without a seed.
struct no_seed_empty_tag_t {};
// Per table hash salt. This gets mixed into H1 to randomize iteration order
// per-table.
// The seed is needed to ensure non-determinism of iteration order.
class PerTableSeed {
public:
// The number of bits in the seed.
// It is big enough to ensure non-determinism of iteration order.
// We store the seed inside a uint64_t together with size and other metadata.
static constexpr size_t kBitCount = 19;
// Returns the seed for the table. Only the lowest kBitCount are non zero.
size_t seed() const { return seed_; }
private:
friend class HashtableSize;
explicit PerTableSeed(size_t seed) : seed_(seed) {}
const size_t seed_;
};
// Returns next seed base number that is used for generating per-table seeds.
// Only the lowest PerTableSeed::kBitCount bits are used for actual hash table
// seed.
inline size_t NextSeedBaseNumber() {
thread_local size_t seed = reinterpret_cast<uintptr_t>(&seed);
if constexpr (sizeof(size_t) == 4) {
seed += uint32_t{0xcc9e2d51};
} else {
seed += uint64_t{0xdcb22ca68cb134ed};
}
return seed;
}
// The size and also has additionally
// 1) one bit that stores whether we have infoz.
// 2) PerTableSeed::kBitCount bits for the seed.
class HashtableSize {
public:
static constexpr size_t kSizeBitCount = 64 - PerTableSeed::kBitCount - 1;
explicit HashtableSize(uninitialized_tag_t) {}
explicit HashtableSize(no_seed_empty_tag_t) : data_(0) {}
explicit HashtableSize(full_soo_tag_t) : data_(kSizeOneNoMetadata) {}
// Returns actual size of the table.
size_t size() const { return static_cast<size_t>(data_ >> kSizeShift); }
void increment_size() { data_ += kSizeOneNoMetadata; }
void increment_size(size_t size) {
data_ += static_cast<uint64_t>(size) * kSizeOneNoMetadata;
}
void decrement_size() { data_ -= kSizeOneNoMetadata; }
// Returns true if the table is empty.
bool empty() const { return data_ < kSizeOneNoMetadata; }
// Sets the size to zero, but keeps all the metadata bits.
void set_size_to_zero_keep_metadata() { data_ = data_ & kMetadataMask; }
PerTableSeed seed() const {
return PerTableSeed(static_cast<size_t>(data_) & kSeedMask);
}
void generate_new_seed() {
size_t seed = NextSeedBaseNumber();
data_ = (data_ & ~kSeedMask) | (seed & kSeedMask);
}
// Returns true if the table has infoz.
bool has_infoz() const {
return ABSL_PREDICT_FALSE((data_ & kHasInfozMask) != 0);
}
// Sets the has_infoz bit.
void set_has_infoz() { data_ |= kHasInfozMask; }
private:
static constexpr size_t kSizeShift = 64 - kSizeBitCount;
static constexpr uint64_t kSizeOneNoMetadata = uint64_t{1} << kSizeShift;
static constexpr uint64_t kMetadataMask = kSizeOneNoMetadata - 1;
static constexpr uint64_t kSeedMask =
(uint64_t{1} << PerTableSeed::kBitCount) - 1;
// The next bit after the seed.
static constexpr uint64_t kHasInfozMask = kSeedMask + 1;
uint64_t data_;
};
// Extracts the H1 portion of a hash: 57 bits mixed with a per-table seed.
inline size_t H1(size_t hash, PerTableSeed seed) {
return (hash >> 7) ^ seed.seed();
}
// Extracts the H2 portion of a hash: the 7 bits not used for H1.
//
// These are used as an occupied control byte.
inline h2_t H2(size_t hash) { return hash & 0x7F; }
// Mixes a randomly generated per-process seed with `hash` and `ctrl` to
// randomize insertion order within groups.
bool ShouldInsertBackwardsForDebug(size_t capacity, size_t hash,
PerTableSeed seed);
ABSL_ATTRIBUTE_ALWAYS_INLINE inline bool ShouldInsertBackwards(
ABSL_ATTRIBUTE_UNUSED size_t capacity, ABSL_ATTRIBUTE_UNUSED size_t hash,
ABSL_ATTRIBUTE_UNUSED PerTableSeed seed) {
#if defined(NDEBUG)
return false;
#else
return ShouldInsertBackwardsForDebug(capacity, hash, seed);
#endif
}
// Returns insert position for the given mask.
// We want to add entropy even when ASLR is not enabled.
// In debug build we will randomly insert in either the front or back of
// the group.
// TODO(kfm,sbenza): revisit after we do unconditional mixing
template <class Mask>
ABSL_ATTRIBUTE_ALWAYS_INLINE inline auto GetInsertionOffset(
Mask mask, ABSL_ATTRIBUTE_UNUSED size_t capacity,
ABSL_ATTRIBUTE_UNUSED size_t hash,
ABSL_ATTRIBUTE_UNUSED PerTableSeed seed) {
#if defined(NDEBUG)
return mask.LowestBitSet();
#else
return ShouldInsertBackwardsForDebug(capacity, hash, seed)
? mask.HighestBitSet()
: mask.LowestBitSet();
#endif
}
// When there is an insertion with no reserved growth, we rehash with
// probability `min(1, RehashProbabilityConstant() / capacity())`. Using a
// constant divided by capacity ensures that inserting N elements is still O(N)
// in the average case. Using the constant 16 means that we expect to rehash ~8
// times more often than when generations are disabled. We are adding expected
// rehash_probability * #insertions/capacity_growth = 16/capacity * ((7/8 -
// 7/16) * capacity)/capacity_growth = ~7 extra rehashes per capacity growth.
inline size_t RehashProbabilityConstant() { return 16; }
class CommonFieldsGenerationInfoEnabled {
// A sentinel value for reserved_growth_ indicating that we just ran out of
// reserved growth on the last insertion. When reserve is called and then
// insertions take place, reserved_growth_'s state machine is N, ..., 1,
// kReservedGrowthJustRanOut, 0.
static constexpr size_t kReservedGrowthJustRanOut =
(std::numeric_limits<size_t>::max)();
public:
CommonFieldsGenerationInfoEnabled() = default;
CommonFieldsGenerationInfoEnabled(CommonFieldsGenerationInfoEnabled&& that)
: reserved_growth_(that.reserved_growth_),
reservation_size_(that.reservation_size_),
generation_(that.generation_) {
that.reserved_growth_ = 0;
that.reservation_size_ = 0;
that.generation_ = EmptyGeneration();
}
CommonFieldsGenerationInfoEnabled& operator=(
CommonFieldsGenerationInfoEnabled&&) = default;
// Whether we should rehash on insert in order to detect bugs of using invalid
// references. We rehash on the first insertion after reserved_growth_ reaches
// 0 after a call to reserve. We also do a rehash with low probability
// whenever reserved_growth_ is zero.
bool should_rehash_for_bug_detection_on_insert(PerTableSeed seed,
size_t capacity) const;
// Similar to above, except that we don't depend on reserved_growth_.
bool should_rehash_for_bug_detection_on_move(PerTableSeed seed,
size_t capacity) const;
void maybe_increment_generation_on_insert() {
if (reserved_growth_ == kReservedGrowthJustRanOut) reserved_growth_ = 0;
if (reserved_growth_ > 0) {
if (--reserved_growth_ == 0) reserved_growth_ = kReservedGrowthJustRanOut;
} else {
increment_generation();
}
}
void increment_generation() { *generation_ = NextGeneration(*generation_); }
void reset_reserved_growth(size_t reservation, size_t size) {
reserved_growth_ = reservation - size;
}
size_t reserved_growth() const { return reserved_growth_; }
void set_reserved_growth(size_t r) { reserved_growth_ = r; }
size_t reservation_size() const { return reservation_size_; }
void set_reservation_size(size_t r) { reservation_size_ = r; }
GenerationType generation() const { return *generation_; }
void set_generation(GenerationType g) { *generation_ = g; }
GenerationType* generation_ptr() const { return generation_; }
void set_generation_ptr(GenerationType* g) { generation_ = g; }
private:
// The number of insertions remaining that are guaranteed to not rehash due to
// a prior call to reserve. Note: we store reserved growth in addition to
// reservation size because calls to erase() decrease size_ but don't decrease
// reserved growth.
size_t reserved_growth_ = 0;
// The maximum argument to reserve() since the container was cleared. We need
// to keep track of this, in addition to reserved growth, because we reset
// reserved growth to this when erase(begin(), end()) is called.
size_t reservation_size_ = 0;
// Pointer to the generation counter, which is used to validate iterators and
// is stored in the backing array between the control bytes and the slots.
// Note that we can't store the generation inside the container itself and
// keep a pointer to the container in the iterators because iterators must
// remain valid when the container is moved.
// Note: we could derive this pointer from the control pointer, but it makes
// the code more complicated, and there's a benefit in having the sizes of
// raw_hash_set in sanitizer mode and non-sanitizer mode a bit more different,
// which is that tests are less likely to rely on the size remaining the same.
GenerationType* generation_ = EmptyGeneration();
};
class CommonFieldsGenerationInfoDisabled {
public:
CommonFieldsGenerationInfoDisabled() = default;
CommonFieldsGenerationInfoDisabled(CommonFieldsGenerationInfoDisabled&&) =
default;
CommonFieldsGenerationInfoDisabled& operator=(
CommonFieldsGenerationInfoDisabled&&) = default;
bool should_rehash_for_bug_detection_on_insert(PerTableSeed, size_t) const {
return false;
}
bool should_rehash_for_bug_detection_on_move(PerTableSeed, size_t) const {
return false;
}
void maybe_increment_generation_on_insert() {}
void increment_generation() {}
void reset_reserved_growth(size_t, size_t) {}
size_t reserved_growth() const { return 0; }
void set_reserved_growth(size_t) {}
size_t reservation_size() const { return 0; }
void set_reservation_size(size_t) {}
GenerationType generation() const { return 0; }
void set_generation(GenerationType) {}
GenerationType* generation_ptr() const { return nullptr; }
void set_generation_ptr(GenerationType*) {}
};
class HashSetIteratorGenerationInfoEnabled {
public:
HashSetIteratorGenerationInfoEnabled() = default;
explicit HashSetIteratorGenerationInfoEnabled(
const GenerationType* generation_ptr)
: generation_ptr_(generation_ptr), generation_(*generation_ptr) {}
GenerationType generation() const { return generation_; }
void reset_generation() { generation_ = *generation_ptr_; }
const GenerationType* generation_ptr() const { return generation_ptr_; }
void set_generation_ptr(const GenerationType* ptr) { generation_ptr_ = ptr; }
private:
const GenerationType* generation_ptr_ = EmptyGeneration();
GenerationType generation_ = *generation_ptr_;
};
class HashSetIteratorGenerationInfoDisabled {
public:
HashSetIteratorGenerationInfoDisabled() = default;
explicit HashSetIteratorGenerationInfoDisabled(const GenerationType*) {}
GenerationType generation() const { return 0; }
void reset_generation() {}
const GenerationType* generation_ptr() const { return nullptr; }
void set_generation_ptr(const GenerationType*) {}
};
#ifdef ABSL_SWISSTABLE_ENABLE_GENERATIONS
using CommonFieldsGenerationInfo = CommonFieldsGenerationInfoEnabled;
using HashSetIteratorGenerationInfo = HashSetIteratorGenerationInfoEnabled;
#else
using CommonFieldsGenerationInfo = CommonFieldsGenerationInfoDisabled;
using HashSetIteratorGenerationInfo = HashSetIteratorGenerationInfoDisabled;
#endif
// Stored the information regarding number of slots we can still fill
// without needing to rehash.
//
// We want to ensure sufficient number of empty slots in the table in order
// to keep probe sequences relatively short. Empty slot in the probe group
// is required to stop probing.
//
// Tombstones (kDeleted slots) are not included in the growth capacity,
// because we'd like to rehash when the table is filled with tombstones and/or
// full slots.
//
// GrowthInfo also stores a bit that encodes whether table may have any
// deleted slots.
// Most of the tables (>95%) have no deleted slots, so some functions can
// be more efficient with this information.
//
// Callers can also force a rehash via the standard `rehash(0)`,
// which will recompute this value as a side-effect.
//
// See also `CapacityToGrowth()`.
class GrowthInfo {
public:
// Leaves data member uninitialized.
GrowthInfo() = default;
// Initializes the GrowthInfo assuming we can grow `growth_left` elements
// and there are no kDeleted slots in the table.
void InitGrowthLeftNoDeleted(size_t growth_left) {
growth_left_info_ = growth_left;
}
// Overwrites single full slot with an empty slot.
void OverwriteFullAsEmpty() { ++growth_left_info_; }
// Overwrites single empty slot with a full slot.
void OverwriteEmptyAsFull() {
ABSL_SWISSTABLE_ASSERT(GetGrowthLeft() > 0);
--growth_left_info_;
}
// Overwrites several empty slots with full slots.
void OverwriteManyEmptyAsFull(size_t count) {
ABSL_SWISSTABLE_ASSERT(GetGrowthLeft() >= count);
growth_left_info_ -= count;
}
// Overwrites specified control element with full slot.
void OverwriteControlAsFull(ctrl_t ctrl) {
ABSL_SWISSTABLE_ASSERT(GetGrowthLeft() >=
static_cast<size_t>(IsEmpty(ctrl)));
growth_left_info_ -= static_cast<size_t>(IsEmpty(ctrl));
}
// Overwrites single full slot with a deleted slot.
void OverwriteFullAsDeleted() { growth_left_info_ |= kDeletedBit; }
// Returns true if table satisfies two properties:
// 1. Guaranteed to have no kDeleted slots.
// 2. There is a place for at least one element to grow.
bool HasNoDeletedAndGrowthLeft() const {
return static_cast<std::make_signed_t<size_t>>(growth_left_info_) > 0;
}
// Returns true if the table satisfies two properties:
// 1. Guaranteed to have no kDeleted slots.
// 2. There is no growth left.
bool HasNoGrowthLeftAndNoDeleted() const { return growth_left_info_ == 0; }
// Returns true if GetGrowthLeft() == 0, but must be called only if
// HasNoDeleted() is false. It is slightly more efficient.
bool HasNoGrowthLeftAssumingMayHaveDeleted() const {
ABSL_SWISSTABLE_ASSERT(!HasNoDeleted());
return growth_left_info_ == kDeletedBit;
}
// Returns true if table guaranteed to have no kDeleted slots.
bool HasNoDeleted() const {
return static_cast<std::make_signed_t<size_t>>(growth_left_info_) >= 0;
}
// Returns the number of elements left to grow.
size_t GetGrowthLeft() const { return growth_left_info_ & kGrowthLeftMask; }
private:
static constexpr size_t kGrowthLeftMask = ((~size_t{}) >> 1);
static constexpr size_t kDeletedBit = ~kGrowthLeftMask;
// Topmost bit signal whenever there are deleted slots.
size_t growth_left_info_;
};
static_assert(sizeof(GrowthInfo) == sizeof(size_t), "");
static_assert(alignof(GrowthInfo) == alignof(size_t), "");
// Returns whether `n` is a valid capacity (i.e., number of slots).
//
// A valid capacity is a non-zero integer `2^m - 1`.
constexpr bool IsValidCapacity(size_t n) { return ((n + 1) & n) == 0 && n > 0; }
// Returns the number of "cloned control bytes".
//
// This is the number of control bytes that are present both at the beginning
// of the control byte array and at the end, such that we can create a
// `Group::kWidth`-width probe window starting from any control byte.
constexpr size_t NumClonedBytes() { return Group::kWidth - 1; }
// Returns the number of control bytes including cloned.
constexpr size_t NumControlBytes(size_t capacity) {
return capacity + 1 + NumClonedBytes();
}
// Computes the offset from the start of the backing allocation of control.
// infoz and growth_info are stored at the beginning of the backing array.
constexpr static size_t ControlOffset(bool has_infoz) {
return (has_infoz ? sizeof(HashtablezInfoHandle) : 0) + sizeof(GrowthInfo);
}
// Helper class for computing offsets and allocation size of hash set fields.
class RawHashSetLayout {
public:
explicit RawHashSetLayout(size_t capacity, size_t slot_size,
size_t slot_align, bool has_infoz)
: control_offset_(ControlOffset(has_infoz)),
generation_offset_(control_offset_ + NumControlBytes(capacity)),
slot_offset_(
(generation_offset_ + NumGenerationBytes() + slot_align - 1) &
(~slot_align + 1)),
alloc_size_(slot_offset_ + capacity * slot_size) {
ABSL_SWISSTABLE_ASSERT(IsValidCapacity(capacity));
ABSL_SWISSTABLE_ASSERT(
slot_size <=
((std::numeric_limits<size_t>::max)() - slot_offset_) / capacity);
}
// Returns precomputed offset from the start of the backing allocation of
// control.
size_t control_offset() const { return control_offset_; }
// Given the capacity of a table, computes the offset (from the start of the
// backing allocation) of the generation counter (if it exists).
size_t generation_offset() const { return generation_offset_; }
// Given the capacity of a table, computes the offset (from the start of the
// backing allocation) at which the slots begin.
size_t slot_offset() const { return slot_offset_; }
// Given the capacity of a table, computes the total size of the backing
// array.
size_t alloc_size() const { return alloc_size_; }
private:
size_t control_offset_;
size_t generation_offset_;
size_t slot_offset_;
size_t alloc_size_;
};
struct HashtableFreeFunctionsAccess;
// Suppress erroneous uninitialized memory errors on GCC. For example, GCC
// thinks that the call to slot_array() in find_or_prepare_insert() is reading
// uninitialized memory, but slot_array is only called there when the table is
// non-empty and this memory is initialized when the table is non-empty.
#if !defined(__clang__) && defined(__GNUC__)
#define ABSL_SWISSTABLE_IGNORE_UNINITIALIZED(x) \
_Pragma("GCC diagnostic push") \
_Pragma("GCC diagnostic ignored \"-Wmaybe-uninitialized\"") \
_Pragma("GCC diagnostic ignored \"-Wuninitialized\"") x; \
_Pragma("GCC diagnostic pop")
#define ABSL_SWISSTABLE_IGNORE_UNINITIALIZED_RETURN(x) \
ABSL_SWISSTABLE_IGNORE_UNINITIALIZED(return x)
#else
#define ABSL_SWISSTABLE_IGNORE_UNINITIALIZED(x) x
#define ABSL_SWISSTABLE_IGNORE_UNINITIALIZED_RETURN(x) return x
#endif
// This allows us to work around an uninitialized memory warning when
// constructing begin() iterators in empty hashtables.
union MaybeInitializedPtr {
void* get() const { ABSL_SWISSTABLE_IGNORE_UNINITIALIZED_RETURN(p); }
void set(void* ptr) { p = ptr; }
void* p;
};
struct HeapPtrs {
explicit HeapPtrs(uninitialized_tag_t) {}
explicit HeapPtrs(ctrl_t* c) : control(c) {}
// The control bytes (and, also, a pointer near to the base of the backing
// array).
//
// This contains `capacity + 1 + NumClonedBytes()` entries, even
// when the table is empty (hence EmptyGroup).
//
// Note that growth_info is stored immediately before this pointer.
// May be uninitialized for SOO tables.
ctrl_t* control;
// The beginning of the slots, located at `SlotOffset()` bytes after
// `control`. May be uninitialized for empty tables.
// Note: we can't use `slots` because Qt defines "slots" as a macro.
MaybeInitializedPtr slot_array;
};
// Returns the maximum size of the SOO slot.
constexpr size_t MaxSooSlotSize() { return sizeof(HeapPtrs); }
// Manages the backing array pointers or the SOO slot. When raw_hash_set::is_soo
// is true, the SOO slot is stored in `soo_data`. Otherwise, we use `heap`.
union HeapOrSoo {
explicit HeapOrSoo(uninitialized_tag_t) : heap(uninitialized_tag_t{}) {}
explicit HeapOrSoo(ctrl_t* c) : heap(c) {}
ctrl_t*& control() {
ABSL_SWISSTABLE_IGNORE_UNINITIALIZED_RETURN(heap.control);
}
ctrl_t* control() const {
ABSL_SWISSTABLE_IGNORE_UNINITIALIZED_RETURN(heap.control);
}
MaybeInitializedPtr& slot_array() {
ABSL_SWISSTABLE_IGNORE_UNINITIALIZED_RETURN(heap.slot_array);
}
MaybeInitializedPtr slot_array() const {
ABSL_SWISSTABLE_IGNORE_UNINITIALIZED_RETURN(heap.slot_array);
}
void* get_soo_data() {
ABSL_SWISSTABLE_IGNORE_UNINITIALIZED_RETURN(soo_data);
}
const void* get_soo_data() const {
ABSL_SWISSTABLE_IGNORE_UNINITIALIZED_RETURN(soo_data);
}
HeapPtrs heap;
unsigned char soo_data[MaxSooSlotSize()];
};
// CommonFields hold the fields in raw_hash_set that do not depend
// on template parameters. This allows us to conveniently pass all
// of this state to helper functions as a single argument.
class CommonFields : public CommonFieldsGenerationInfo {
public:
explicit CommonFields(soo_tag_t)
: capacity_(SooCapacity()),
size_(no_seed_empty_tag_t{}),
heap_or_soo_(uninitialized_tag_t{}) {}
explicit CommonFields(full_soo_tag_t)
: capacity_(SooCapacity()),
size_(full_soo_tag_t{}),
heap_or_soo_(uninitialized_tag_t{}) {}
explicit CommonFields(non_soo_tag_t)
: capacity_(0),
size_(no_seed_empty_tag_t{}),
heap_or_soo_(EmptyGroup()) {}
// For use in swapping.
explicit CommonFields(uninitialized_tag_t)
: size_(uninitialized_tag_t{}), heap_or_soo_(uninitialized_tag_t{}) {}
// Not copyable
CommonFields(const CommonFields&) = delete;
CommonFields& operator=(const CommonFields&) = delete;
// Copy with guarantee that it is not SOO.
CommonFields(non_soo_tag_t, const CommonFields& that)
: capacity_(that.capacity_),
size_(that.size_),
heap_or_soo_(that.heap_or_soo_) {
}
// Movable
CommonFields(CommonFields&& that) = default;
CommonFields& operator=(CommonFields&&) = default;
template <bool kSooEnabled>
static CommonFields CreateDefault() {
return kSooEnabled ? CommonFields{soo_tag_t{}}
: CommonFields{non_soo_tag_t{}};
}
// The inline data for SOO is written on top of control_/slots_.
const void* soo_data() const { return heap_or_soo_.get_soo_data(); }
void* soo_data() { return heap_or_soo_.get_soo_data(); }
ctrl_t* control() const { return heap_or_soo_.control(); }
// When we set the control bytes, we also often want to generate a new seed.
// So we bundle these two operations together to make sure we don't forget to
// generate a new seed.
// The table will be invalidated if
// `kGenerateSeed && !empty() && !is_single_group(capacity())` because H1 is
// being changed. In such cases, we will need to rehash the table.
template <bool kGenerateSeed>
void set_control(ctrl_t* c) {
heap_or_soo_.control() = c;
if constexpr (kGenerateSeed) {
generate_new_seed();
}
}
void* backing_array_start() const {
// growth_info (and maybe infoz) is stored before control bytes.
ABSL_SWISSTABLE_ASSERT(
reinterpret_cast<uintptr_t>(control()) % alignof(size_t) == 0);
return control() - ControlOffset(has_infoz());
}
// Note: we can't use slots() because Qt defines "slots" as a macro.
void* slot_array() const { return heap_or_soo_.slot_array().get(); }
MaybeInitializedPtr slots_union() const { return heap_or_soo_.slot_array(); }
void set_slots(void* s) { heap_or_soo_.slot_array().set(s); }
// The number of filled slots.
size_t size() const { return size_.size(); }
// Sets the size to zero, but keeps hashinfoz bit and seed.
void set_size_to_zero() { size_.set_size_to_zero_keep_metadata(); }
void set_empty_soo() {
AssertInSooMode();
size_ = HashtableSize(no_seed_empty_tag_t{});
}
void set_full_soo() {
AssertInSooMode();
size_ = HashtableSize(full_soo_tag_t{});
}
void increment_size() {
ABSL_SWISSTABLE_ASSERT(size() < capacity());
size_.increment_size();
}
void increment_size(size_t n) {
ABSL_SWISSTABLE_ASSERT(size() + n <= capacity());
size_.increment_size(n);
}
void decrement_size() {
ABSL_SWISSTABLE_ASSERT(!empty());
size_.decrement_size();
}
bool empty() const { return size_.empty(); }
// The seed used for the H1 part of the hash function.
PerTableSeed seed() const { return size_.seed(); }
// Generates a new seed for the H1 part of the hash function.
// The table will be invalidated if
// `kGenerateSeed && !empty() && !is_single_group(capacity())` because H1 is
// being changed. In such cases, we will need to rehash the table.
void generate_new_seed() { size_.generate_new_seed(); }
// The total number of available slots.
size_t capacity() const { return capacity_; }
void set_capacity(size_t c) {
// We allow setting above the max valid capacity for debugging purposes.
ABSL_SWISSTABLE_ASSERT(c == 0 || IsValidCapacity(c) ||
c > kAboveMaxValidCapacity);
capacity_ = c;
}
// The number of slots we can still fill without needing to rehash.
// This is stored in the heap allocation before the control bytes.
// TODO(b/289225379): experiment with moving growth_info back inline to
// increase room for SOO.
size_t growth_left() const { return growth_info().GetGrowthLeft(); }
GrowthInfo& growth_info() {
auto* gl_ptr = reinterpret_cast<GrowthInfo*>(control()) - 1;
ABSL_SWISSTABLE_ASSERT(
reinterpret_cast<uintptr_t>(gl_ptr) % alignof(GrowthInfo) == 0);
return *gl_ptr;
}
GrowthInfo growth_info() const {
return const_cast<CommonFields*>(this)->growth_info();
}
bool has_infoz() const { return size_.has_infoz(); }
void set_has_infoz() { size_.set_has_infoz(); }
HashtablezInfoHandle infoz() {
return has_infoz()
? *reinterpret_cast<HashtablezInfoHandle*>(backing_array_start())
: HashtablezInfoHandle();
}
void set_infoz(HashtablezInfoHandle infoz) {
ABSL_SWISSTABLE_ASSERT(has_infoz());
*reinterpret_cast<HashtablezInfoHandle*>(backing_array_start()) = infoz;
}
bool should_rehash_for_bug_detection_on_insert() const {
if constexpr (!SwisstableGenerationsEnabled()) {
return false;
}
// As an optimization, we avoid calling ShouldRehashForBugDetection if we
// will end up rehashing anyways.
if (growth_left() == 0) return false;
return CommonFieldsGenerationInfo::
should_rehash_for_bug_detection_on_insert(seed(), capacity());
}
bool should_rehash_for_bug_detection_on_move() const {
return CommonFieldsGenerationInfo::should_rehash_for_bug_detection_on_move(
seed(), capacity());
}
void reset_reserved_growth(size_t reservation) {
CommonFieldsGenerationInfo::reset_reserved_growth(reservation, size());
}
// The size of the backing array allocation.
size_t alloc_size(size_t slot_size, size_t slot_align) const {
return RawHashSetLayout(capacity(), slot_size, slot_align, has_infoz())
.alloc_size();
}
// Move fields other than heap_or_soo_.
void move_non_heap_or_soo_fields(CommonFields& that) {
static_cast<CommonFieldsGenerationInfo&>(*this) =
std::move(static_cast<CommonFieldsGenerationInfo&>(that));
capacity_ = that.capacity_;
size_ = that.size_;
}
// Returns the number of control bytes set to kDeleted. For testing only.
size_t TombstonesCount() const {
return static_cast<size_t>(
std::count(control(), control() + capacity(), ctrl_t::kDeleted));
}
// Helper to enable sanitizer mode validation to protect against reentrant
// calls during element constructor/destructor.
template <typename F>
void RunWithReentrancyGuard(F f) {
#ifdef NDEBUG
f();
return;
#endif
const size_t cap = capacity();
set_capacity(InvalidCapacity::kReentrance);
f();
set_capacity(cap);
}
private:
// We store the has_infoz bit in the lowest bit of size_.
static constexpr size_t HasInfozShift() { return 1; }
static constexpr size_t HasInfozMask() {
return (size_t{1} << HasInfozShift()) - 1;
}
// We can't assert that SOO is enabled because we don't have SooEnabled(), but
// we assert what we can.
void AssertInSooMode() const {
ABSL_SWISSTABLE_ASSERT(capacity() == SooCapacity());
ABSL_SWISSTABLE_ASSERT(!has_infoz());
}
// The number of slots in the backing array. This is always 2^N-1 for an
// integer N. NOTE: we tried experimenting with compressing the capacity and
// storing it together with size_: (a) using 6 bits to store the corresponding
// power (N in 2^N-1), and (b) storing 2^N as the most significant bit of
// size_ and storing size in the low bits. Both of these experiments were
// regressions, presumably because we need capacity to do find operations.
size_t capacity_;
// TODO(b/289225379): we could put size_ into HeapOrSoo and make capacity_
// encode the size in SOO case. We would be making size()/capacity() more
// expensive in order to have more SOO space.
HashtableSize size_;
// Either the control/slots pointers or the SOO slot.
HeapOrSoo heap_or_soo_;
};
template <class Policy, class Hash, class Eq, class Alloc>
class raw_hash_set;
// Returns the next valid capacity after `n`.
constexpr size_t NextCapacity(size_t n) {
ABSL_SWISSTABLE_ASSERT(IsValidCapacity(n) || n == 0);
return n * 2 + 1;
}
// Applies the following mapping to every byte in the control array:
// * kDeleted -> kEmpty
// * kEmpty -> kEmpty
// * _ -> kDeleted
// PRECONDITION:
// IsValidCapacity(capacity)
// ctrl[capacity] == ctrl_t::kSentinel
// ctrl[i] != ctrl_t::kSentinel for all i < capacity
void ConvertDeletedToEmptyAndFullToDeleted(ctrl_t* ctrl, size_t capacity);
// Converts `n` into the next valid capacity, per `IsValidCapacity`.
constexpr size_t NormalizeCapacity(size_t n) {
return n ? ~size_t{} >> countl_zero(n) : 1;
}
// General notes on capacity/growth methods below:
// - We use 7/8th as maximum load factor. For 16-wide groups, that gives an
// average of two empty slots per group.
// - For (capacity+1) >= Group::kWidth, growth is 7/8*capacity.
// - For (capacity+1) < Group::kWidth, growth == capacity. In this case, we
// never need to probe (the whole table fits in one group) so we don't need a
// load factor less than 1.
// Given `capacity`, applies the load factor; i.e., it returns the maximum
// number of values we should put into the table before a resizing rehash.
constexpr size_t CapacityToGrowth(size_t capacity) {
ABSL_SWISSTABLE_ASSERT(IsValidCapacity(capacity));
// `capacity*7/8`
if (Group::kWidth == 8 && capacity == 7) {
// x-x/8 does not work when x==7.
return 6;
}
return capacity - capacity / 8;
}
// Given `growth`, "unapplies" the load factor to find how large the capacity
// should be to stay within the load factor.
//
// This might not be a valid capacity and `NormalizeCapacity()` should be
// called on this.
inline size_t GrowthToLowerboundCapacity(size_t growth) {
// `growth*8/7`
if (Group::kWidth == 8 && growth == 7) {
// x+(x-1)/7 does not work when x==7.
return 8;
}
return growth + static_cast<size_t>((static_cast<int64_t>(growth) - 1) / 7);
}
template <class InputIter>
size_t SelectBucketCountForIterRange(InputIter first, InputIter last,
size_t bucket_count) {
if (bucket_count != 0) {
return bucket_count;
}
if (base_internal::IsAtLeastIterator<std::random_access_iterator_tag,
InputIter>()) {
return GrowthToLowerboundCapacity(
static_cast<size_t>(std::distance(first, last)));
}
return 0;
}
constexpr bool SwisstableDebugEnabled() {
#if defined(ABSL_SWISSTABLE_ENABLE_GENERATIONS) || \
ABSL_OPTION_HARDENED == 1 || !defined(NDEBUG)
return true;
#else
return false;
#endif
}
inline void AssertIsFull(const ctrl_t* ctrl, GenerationType generation,
const GenerationType* generation_ptr,
const char* operation) {
if (!SwisstableDebugEnabled()) return;
// `SwisstableDebugEnabled()` is also true for release builds with hardening
// enabled. To minimize their impact in those builds:
// - use `ABSL_PREDICT_FALSE()` to provide a compiler hint for code layout
// - use `ABSL_RAW_LOG()` with a format string to reduce code size and improve
// the chances that the hot paths will be inlined.
if (ABSL_PREDICT_FALSE(ctrl == nullptr)) {
ABSL_RAW_LOG(FATAL, "%s called on end() iterator.", operation);
}
if (ABSL_PREDICT_FALSE(ctrl == EmptyGroup())) {
ABSL_RAW_LOG(FATAL, "%s called on default-constructed iterator.",
operation);
}
if (SwisstableGenerationsEnabled()) {
if (ABSL_PREDICT_FALSE(generation != *generation_ptr)) {
ABSL_RAW_LOG(FATAL,
"%s called on invalid iterator. The table could have "
"rehashed or moved since this iterator was initialized.",
operation);
}
if (ABSL_PREDICT_FALSE(!IsFull(*ctrl))) {
ABSL_RAW_LOG(
FATAL,
"%s called on invalid iterator. The element was likely erased.",
operation);
}
} else {
if (ABSL_PREDICT_FALSE(!IsFull(*ctrl))) {
ABSL_RAW_LOG(
FATAL,
"%s called on invalid iterator. The element might have been erased "
"or the table might have rehashed. Consider running with "
"--config=asan to diagnose rehashing issues.",
operation);
}
}
}
// Note that for comparisons, null/end iterators are valid.
inline void AssertIsValidForComparison(const ctrl_t* ctrl,
GenerationType generation,
const GenerationType* generation_ptr) {
if (!SwisstableDebugEnabled()) return;
const bool ctrl_is_valid_for_comparison =
ctrl == nullptr || ctrl == EmptyGroup() || IsFull(*ctrl);
if (SwisstableGenerationsEnabled()) {
if (ABSL_PREDICT_FALSE(generation != *generation_ptr)) {
ABSL_RAW_LOG(FATAL,
"Invalid iterator comparison. The table could have rehashed "
"or moved since this iterator was initialized.");
}
if (ABSL_PREDICT_FALSE(!ctrl_is_valid_for_comparison)) {
ABSL_RAW_LOG(
FATAL, "Invalid iterator comparison. The element was likely erased.");
}
} else {
ABSL_HARDENING_ASSERT(
ctrl_is_valid_for_comparison &&
"Invalid iterator comparison. The element might have been erased or "
"the table might have rehashed. Consider running with --config=asan to "
"diagnose rehashing issues.");
}
}
// If the two iterators come from the same container, then their pointers will
// interleave such that ctrl_a <= ctrl_b < slot_a <= slot_b or vice/versa.
// Note: we take slots by reference so that it's not UB if they're uninitialized
// as long as we don't read them (when ctrl is null).
inline bool AreItersFromSameContainer(const ctrl_t* ctrl_a,
const ctrl_t* ctrl_b,
const void* const& slot_a,
const void* const& slot_b) {
// If either control byte is null, then we can't tell.
if (ctrl_a == nullptr || ctrl_b == nullptr) return true;
const bool a_is_soo = IsSooControl(ctrl_a);
if (a_is_soo != IsSooControl(ctrl_b)) return false;
if (a_is_soo) return slot_a == slot_b;
const void* low_slot = slot_a;
const void* hi_slot = slot_b;
if (ctrl_a > ctrl_b) {
std::swap(ctrl_a, ctrl_b);
std::swap(low_slot, hi_slot);
}
return ctrl_b < low_slot && low_slot <= hi_slot;
}
// Asserts that two iterators come from the same container.
// Note: we take slots by reference so that it's not UB if they're uninitialized
// as long as we don't read them (when ctrl is null).
inline void AssertSameContainer(const ctrl_t* ctrl_a, const ctrl_t* ctrl_b,
const void* const& slot_a,
const void* const& slot_b,
const GenerationType* generation_ptr_a,
const GenerationType* generation_ptr_b) {
if (!SwisstableDebugEnabled()) return;
// `SwisstableDebugEnabled()` is also true for release builds with hardening
// enabled. To minimize their impact in those builds:
// - use `ABSL_PREDICT_FALSE()` to provide a compiler hint for code layout
// - use `ABSL_RAW_LOG()` with a format string to reduce code size and improve
// the chances that the hot paths will be inlined.
// fail_if(is_invalid, message) crashes when is_invalid is true and provides
// an error message based on `message`.
const auto fail_if = [](bool is_invalid, const char* message) {
if (ABSL_PREDICT_FALSE(is_invalid)) {
ABSL_RAW_LOG(FATAL, "Invalid iterator comparison. %s", message);
}
};
const bool a_is_default = ctrl_a == EmptyGroup();
const bool b_is_default = ctrl_b == EmptyGroup();
if (a_is_default && b_is_default) return;
fail_if(a_is_default != b_is_default,
"Comparing default-constructed hashtable iterator with a "
"non-default-constructed hashtable iterator.");
if (SwisstableGenerationsEnabled()) {
if (ABSL_PREDICT_TRUE(generation_ptr_a == generation_ptr_b)) return;
// Users don't need to know whether the tables are SOO so don't mention SOO
// in the debug message.
const bool a_is_soo = IsSooControl(ctrl_a);
const bool b_is_soo = IsSooControl(ctrl_b);
fail_if(a_is_soo != b_is_soo || (a_is_soo && b_is_soo),
"Comparing iterators from different hashtables.");
const bool a_is_empty = IsEmptyGeneration(generation_ptr_a);
const bool b_is_empty = IsEmptyGeneration(generation_ptr_b);
fail_if(a_is_empty != b_is_empty,
"Comparing an iterator from an empty hashtable with an iterator "
"from a non-empty hashtable.");
fail_if(a_is_empty && b_is_empty,
"Comparing iterators from different empty hashtables.");
const bool a_is_end = ctrl_a == nullptr;
const bool b_is_end = ctrl_b == nullptr;
fail_if(a_is_end || b_is_end,
"Comparing iterator with an end() iterator from a different "
"hashtable.");
fail_if(true, "Comparing non-end() iterators from different hashtables.");
} else {
ABSL_HARDENING_ASSERT_SLOW(
AreItersFromSameContainer(ctrl_a, ctrl_b, slot_a, slot_b) &&
"Invalid iterator comparison. The iterators may be from different "
"containers or the container might have rehashed or moved. Consider "
"running with --config=asan to diagnose issues.");
}
}
struct FindInfo {
size_t offset;
size_t probe_length;
};
// Whether a table is "small". A small table fits entirely into a probing
// group, i.e., has a capacity < `Group::kWidth`.
//
// In small mode we are able to use the whole capacity. The extra control
// bytes give us at least one "empty" control byte to stop the iteration.
// This is important to make 1 a valid capacity.
//
// In small mode only the first `capacity` control bytes after the sentinel
// are valid. The rest contain dummy ctrl_t::kEmpty values that do not
// represent a real slot. This is important to take into account on
// `find_first_non_full()`, where we never try
// `ShouldInsertBackwards()` for small tables.
constexpr bool is_small(size_t capacity) {
return capacity < Group::kWidth - 1;
}
// Whether a table fits entirely into a probing group.
// Arbitrary order of elements in such tables is correct.
constexpr bool is_single_group(size_t capacity) {
return capacity <= Group::kWidth;
}
// Begins a probing operation on `common.control`, using `hash`.
inline probe_seq<Group::kWidth> probe(PerTableSeed seed, const size_t capacity,
size_t hash) {
return probe_seq<Group::kWidth>(H1(hash, seed), capacity);
}
inline probe_seq<Group::kWidth> probe(const CommonFields& common, size_t hash) {
return probe(common.seed(), common.capacity(), hash);
}
// Probes an array of control bits using a probe sequence derived from `hash`,
// and returns the offset corresponding to the first deleted or empty slot.
//
// Behavior when the entire table is full is undefined.
//
// NOTE: this function must work with tables having both empty and deleted
// slots in the same group. Such tables appear during `erase()`.
template <typename = void>
inline FindInfo find_first_non_full(const CommonFields& common, size_t hash) {
auto seq = probe(common, hash);
const ctrl_t* ctrl = common.control();
const PerTableSeed seed = common.seed();
if (IsEmptyOrDeleted(ctrl[seq.offset()]) &&
!ShouldInsertBackwards(common.capacity(), hash, seed)) {
return {seq.offset(), /*probe_length=*/0};
}
while (true) {
GroupFullEmptyOrDeleted g{ctrl + seq.offset()};
auto mask = g.MaskEmptyOrDeleted();
if (mask) {
return {
seq.offset(GetInsertionOffset(mask, common.capacity(), hash, seed)),
seq.index()};
}
seq.next();
ABSL_SWISSTABLE_ASSERT(seq.index() <= common.capacity() && "full table!");
}
}
// Extern template for inline function keep possibility of inlining.
// When compiler decided to not inline, no symbols will be added to the
// corresponding translation unit.
extern template FindInfo find_first_non_full(const CommonFields&, size_t);
// Non-inlined version of find_first_non_full for use in less
// performance critical routines.
FindInfo find_first_non_full_outofline(const CommonFields&, size_t);
// Sets `ctrl` to `{kEmpty, kSentinel, ..., kEmpty}`, marking the entire
// array as marked as empty.
inline void ResetCtrl(CommonFields& common, size_t slot_size) {
const size_t capacity = common.capacity();
ctrl_t* ctrl = common.control();
std::memset(ctrl, static_cast<int8_t>(ctrl_t::kEmpty),
capacity + 1 + NumClonedBytes());
ctrl[capacity] = ctrl_t::kSentinel;
SanitizerPoisonMemoryRegion(common.slot_array(), slot_size * capacity);
}
// Sets sanitizer poisoning for slot corresponding to control byte being set.
inline void DoSanitizeOnSetCtrl(const CommonFields& c, size_t i, ctrl_t h,
size_t slot_size) {
ABSL_SWISSTABLE_ASSERT(i < c.capacity());
auto* slot_i = static_cast<const char*>(c.slot_array()) + i * slot_size;
if (IsFull(h)) {
SanitizerUnpoisonMemoryRegion(slot_i, slot_size);
} else {
SanitizerPoisonMemoryRegion(slot_i, slot_size);
}
}
// Sets `ctrl[i]` to `h`.
//
// Unlike setting it directly, this function will perform bounds checks and
// mirror the value to the cloned tail if necessary.
inline void SetCtrl(const CommonFields& c, size_t i, ctrl_t h,
size_t slot_size) {
DoSanitizeOnSetCtrl(c, i, h, slot_size);
ctrl_t* ctrl = c.control();
ctrl[i] = h;
ctrl[((i - NumClonedBytes()) & c.capacity()) +
(NumClonedBytes() & c.capacity())] = h;
}
// Overload for setting to an occupied `h2_t` rather than a special `ctrl_t`.
inline void SetCtrl(const CommonFields& c, size_t i, h2_t h, size_t slot_size) {
SetCtrl(c, i, static_cast<ctrl_t>(h), slot_size);
}
// Like SetCtrl, but in a single group table, we can save some operations when
// setting the cloned control byte.
inline void SetCtrlInSingleGroupTable(const CommonFields& c, size_t i, ctrl_t h,
size_t slot_size) {
ABSL_SWISSTABLE_ASSERT(is_single_group(c.capacity()));
DoSanitizeOnSetCtrl(c, i, h, slot_size);
ctrl_t* ctrl = c.control();
ctrl[i] = h;
ctrl[i + c.capacity() + 1] = h;
}
// Overload for setting to an occupied `h2_t` rather than a special `ctrl_t`.
inline void SetCtrlInSingleGroupTable(const CommonFields& c, size_t i, h2_t h,
size_t slot_size) {
SetCtrlInSingleGroupTable(c, i, static_cast<ctrl_t>(h), slot_size);
}
// Like SetCtrl, but in a table with capacity >= Group::kWidth - 1,
// we can save some operations when setting the cloned control byte.
inline void SetCtrlInLargeTable(const CommonFields& c, size_t i, ctrl_t h,
size_t slot_size) {
ABSL_SWISSTABLE_ASSERT(c.capacity() >= Group::kWidth - 1);
DoSanitizeOnSetCtrl(c, i, h, slot_size);
ctrl_t* ctrl = c.control();
ctrl[i] = h;
ctrl[((i - NumClonedBytes()) & c.capacity()) + NumClonedBytes()] = h;
}
// Overload for setting to an occupied `h2_t` rather than a special `ctrl_t`.
inline void SetCtrlInLargeTable(const CommonFields& c, size_t i, h2_t h,
size_t slot_size) {
SetCtrlInLargeTable(c, i, static_cast<ctrl_t>(h), slot_size);
}
// growth_info (which is a size_t) is stored with the backing array.
constexpr size_t BackingArrayAlignment(size_t align_of_slot) {
return (std::max)(align_of_slot, alignof(GrowthInfo));
}
// Returns the address of the ith slot in slots where each slot occupies
// slot_size.
inline void* SlotAddress(void* slot_array, size_t slot, size_t slot_size) {
return static_cast<void*>(static_cast<char*>(slot_array) +
(slot * slot_size));
}
// Iterates over all full slots and calls `cb(const ctrl_t*, void*)`.
// No insertion to the table is allowed during `cb` call.
// Erasure is allowed only for the element passed to the callback.
// The table must not be in SOO mode.
void IterateOverFullSlots(const CommonFields& c, size_t slot_size,
absl::FunctionRef<void(const ctrl_t*, void*)> cb);
template <typename CharAlloc>
constexpr bool ShouldSampleHashtablezInfoForAlloc() {
// Folks with custom allocators often make unwarranted assumptions about the
// behavior of their classes vis-a-vis trivial destructability and what
// calls they will or won't make. Avoid sampling for people with custom
// allocators to get us out of this mess. This is not a hard guarantee but
// a workaround while we plan the exact guarantee we want to provide.
return std::is_same_v<CharAlloc, std::allocator<char>>;
}
template <bool kSooEnabled>
bool ShouldSampleHashtablezInfoOnResize(bool force_sampling,
bool is_hashtablez_eligible,
size_t old_capacity, CommonFields& c) {
if (!is_hashtablez_eligible) return false;
// Force sampling is only allowed for SOO tables.
ABSL_SWISSTABLE_ASSERT(kSooEnabled || !force_sampling);
if (kSooEnabled && force_sampling) {
return true;
}
// In SOO, we sample on the first insertion so if this is an empty SOO case
// (e.g. when reserve is called), then we still need to sample.
if (kSooEnabled && old_capacity == SooCapacity() && c.empty()) {
return ShouldSampleNextTable();
}
if (!kSooEnabled && old_capacity == 0) {
return ShouldSampleNextTable();
}
return false;
}
// Allocates `n` bytes for a backing array.
template <size_t AlignOfBackingArray, typename Alloc>
ABSL_ATTRIBUTE_NOINLINE void* AllocateBackingArray(void* alloc, size_t n) {
return Allocate<AlignOfBackingArray>(static_cast<Alloc*>(alloc), n);
}
template <size_t AlignOfBackingArray, typename Alloc>
ABSL_ATTRIBUTE_NOINLINE void DeallocateBackingArray(
void* alloc, size_t capacity, ctrl_t* ctrl, size_t slot_size,
size_t slot_align, bool had_infoz) {
RawHashSetLayout layout(capacity, slot_size, slot_align, had_infoz);
void* backing_array = ctrl - layout.control_offset();
// Unpoison before returning the memory to the allocator.
SanitizerUnpoisonMemoryRegion(backing_array, layout.alloc_size());
Deallocate<AlignOfBackingArray>(static_cast<Alloc*>(alloc), backing_array,
layout.alloc_size());
}
// PolicyFunctions bundles together some information for a particular
// raw_hash_set<T, ...> instantiation. This information is passed to
// type-erased functions that want to do small amounts of type-specific
// work.
struct PolicyFunctions {
uint32_t key_size;
uint32_t value_size;
uint32_t slot_size;
uint16_t slot_align;
uint8_t soo_capacity;
bool is_hashtablez_eligible;
// Returns the pointer to the hash function stored in the set.
void* (*hash_fn)(CommonFields& common);
// Returns the hash of the pointed-to slot.
size_t (*hash_slot)(const void* hash_fn, void* slot);
// Transfers the contents of `count` slots from src_slot to dst_slot.
// We use ability to transfer several slots in single group table growth.
// TODO(b/382423690): consider having separate `transfer` and `transfer_n`.
void (*transfer)(void* set, void* dst_slot, void* src_slot, size_t count);
// Returns the pointer to the CharAlloc stored in the set.
void* (*get_char_alloc)(CommonFields& common);
// Allocates n bytes for the backing store for common.
void* (*alloc)(void* alloc, size_t n);
// Deallocates the backing store from common.
void (*dealloc)(void* alloc, size_t capacity, ctrl_t* ctrl, size_t slot_size,
size_t slot_align, bool had_infoz);
// Iterates over full slots in old table, finds new positions
// for them and transfers the slots.
// Returns the total probe length.
size_t (*find_new_positions_and_transfer_slots)(CommonFields& common,
ctrl_t* old_ctrl,
void* old_slots,
size_t old_capacity);
};
// Returns the maximum valid size for a table with 1-byte slots.
// This function is an utility shared by MaxValidSize and IsAboveValidSize.
// Template parameter is only used to enable testing.
template <size_t kSizeOfSizeT = sizeof(size_t)>
constexpr size_t MaxValidSizeFor1ByteSlot() {
if constexpr (kSizeOfSizeT == 8) {
return CapacityToGrowth(
static_cast<size_t>(uint64_t{1} << HashtableSize::kSizeBitCount) - 1);
} else {
static_assert(kSizeOfSizeT == 4);
return CapacityToGrowth((size_t{1} << (kSizeOfSizeT * 8 - 2)) - 1);
}
}
// Returns the maximum valid size for a table with provided slot size.
// Template parameter is only used to enable testing.
template <size_t kSizeOfSizeT = sizeof(size_t)>
constexpr size_t MaxValidSize(size_t slot_size) {
if constexpr (kSizeOfSizeT == 8) {
// For small slot sizes we are limited by HashtableSize::kSizeBitCount.
if (slot_size < size_t{1} << (64 - HashtableSize::kSizeBitCount)) {
return MaxValidSizeFor1ByteSlot<kSizeOfSizeT>();
}
return (size_t{1} << (kSizeOfSizeT * 8 - 2)) / slot_size;
} else {
return MaxValidSizeFor1ByteSlot<kSizeOfSizeT>() / slot_size;
}
}
// Returns true if size is larger than the maximum valid size.
// It is an optimization to avoid the division operation in the common case.
// Template parameter is only used to enable testing.
template <size_t kSizeOfSizeT = sizeof(size_t)>
constexpr bool IsAboveValidSize(size_t size, size_t slot_size) {
if constexpr (kSizeOfSizeT == 8) {
// For small slot sizes we are limited by HashtableSize::kSizeBitCount.
if (ABSL_PREDICT_TRUE(slot_size <
(size_t{1} << (64 - HashtableSize::kSizeBitCount)))) {
return size > MaxValidSizeFor1ByteSlot<kSizeOfSizeT>();
}
return size > MaxValidSize<kSizeOfSizeT>(slot_size);
} else {
return uint64_t{size} * slot_size >
MaxValidSizeFor1ByteSlot<kSizeOfSizeT>();
}
}
// Returns the index of the SOO slot when growing from SOO to non-SOO in a
// single group. See also InitializeSmallControlBytesAfterSoo(). It's important
// to use index 1 so that when resizing from capacity 1 to 3, we can still have
// random iteration order between the first two inserted elements.
// I.e. it allows inserting the second element at either index 0 or 2.
constexpr size_t SooSlotIndex() { return 1; }
// Maximum capacity for the algorithm for small table after SOO.
// Note that typical size after SOO is 3, but we allow up to 7.
// Allowing till 16 would require additional store that can be avoided.
constexpr size_t MaxSmallAfterSooCapacity() { return 7; }
// Resizes empty non-allocated table to the capacity to fit new_size elements.
// Requires:
// 1. `c.capacity() == policy.soo_capacity`.
// 2. `c.empty()`.
// 3. `new_size > policy.soo_capacity`.
// The table will be attempted to be sampled.
void ReserveEmptyNonAllocatedTableToFitNewSize(CommonFields& common,
const PolicyFunctions& policy,
size_t new_size);
// The same as ReserveEmptyNonAllocatedTableToFitNewSize, but resizes to the
// next valid capacity after `bucket_count`.
void ReserveEmptyNonAllocatedTableToFitBucketCount(
CommonFields& common, const PolicyFunctions& policy, size_t bucket_count);
// Resizes empty non-allocated SOO table to NextCapacity(SooCapacity()) and
// forces the table to be sampled.
// SOO tables need to switch from SOO to heap in order to store the infoz.
// Requires:
// 1. `c.capacity() == SooCapacity()`.
// 2. `c.empty()`.
void GrowEmptySooTableToNextCapacityForceSampling(
CommonFields& common, const PolicyFunctions& policy);
// Type erased version of raw_hash_set::rehash.
void Rehash(CommonFields& common, const PolicyFunctions& policy, size_t n);
// Type erased version of raw_hash_set::reserve for tables that have an
// allocated backing array.
//
// Requires:
// 1. `c.capacity() > policy.soo_capacity` OR `!c.empty()`.
// Reserving already allocated tables is considered to be a rare case.
void ReserveAllocatedTable(CommonFields& common, const PolicyFunctions& policy,
size_t n);
// Returns the optimal size for memcpy when transferring SOO slot.
// Otherwise, returns the optimal size for memcpy SOO slot transfer
// to SooSlotIndex().
// At the destination we are allowed to copy upto twice more bytes,
// because there is at least one more slot after SooSlotIndex().
// The result must not exceed MaxSooSlotSize().
// Some of the cases are merged to minimize the number of function
// instantiations.
constexpr size_t OptimalMemcpySizeForSooSlotTransfer(
size_t slot_size, size_t max_soo_slot_size = MaxSooSlotSize()) {
static_assert(MaxSooSlotSize() >= 8, "unexpectedly small SOO slot size");
if (slot_size == 1) {
return 1;
}
if (slot_size <= 3) {
return 4;
}
// We are merging 4 and 8 into one case because we expect them to be the
// hottest cases. Copying 8 bytes is as fast on common architectures.
if (slot_size <= 8) {
return 8;
}
if (max_soo_slot_size <= 16) {
return max_soo_slot_size;
}
if (slot_size <= 16) {
return 16;
}
if (max_soo_slot_size <= 24) {
return max_soo_slot_size;
}
static_assert(MaxSooSlotSize() <= 24, "unexpectedly large SOO slot size");
return 24;
}
// Resizes a full SOO table to the NextCapacity(SooCapacity()).
// All possible template combinations are defined in cc file to improve
// compilation time.
template <size_t SooSlotMemcpySize, bool TransferUsesMemcpy>
void GrowFullSooTableToNextCapacity(CommonFields& common,
const PolicyFunctions& policy,
size_t soo_slot_hash);
// As `ResizeFullSooTableToNextCapacity`, except that we also force the SOO
// table to be sampled. SOO tables need to switch from SOO to heap in order to
// store the infoz. No-op if sampling is disabled or not possible.
void GrowFullSooTableToNextCapacityForceSampling(CommonFields& common,
const PolicyFunctions& policy);
// Resizes table with allocated slots and change the table seed.
// Tables with SOO enabled must have capacity > policy.soo_capacity.
// No sampling will be performed since table is already allocated.
void ResizeAllocatedTableWithSeedChange(CommonFields& common,
const PolicyFunctions& policy,
size_t new_capacity);
inline void PrepareInsertCommon(CommonFields& common) {
common.increment_size();
common.maybe_increment_generation_on_insert();
}
// Like prepare_insert, but for the case of inserting into a full SOO table.
size_t PrepareInsertAfterSoo(size_t hash, size_t slot_size,
CommonFields& common);
// ClearBackingArray clears the backing array, either modifying it in place,
// or creating a new one based on the value of "reuse".
// REQUIRES: c.capacity > 0
void ClearBackingArray(CommonFields& c, const PolicyFunctions& policy,
void* alloc, bool reuse, bool soo_enabled);
// Type-erased version of raw_hash_set::erase_meta_only.
void EraseMetaOnly(CommonFields& c, size_t index, size_t slot_size);
// For trivially relocatable types we use memcpy directly. This allows us to
// share the same function body for raw_hash_set instantiations that have the
// same slot size as long as they are relocatable.
template <size_t SizeOfSlot>
ABSL_ATTRIBUTE_NOINLINE void TransferRelocatable(void*, void* dst, void* src,
size_t count) {
// TODO(b/382423690): Experiment with transfer and transfer_n.
// TODO(b/382423690): Experiment with making specialization for power of 2 and
// non power of 2. This would require passing the size of the slot.
memcpy(dst, src, SizeOfSlot * count);
}
// Returns a pointer to `common`. This is used to implement type erased
// raw_hash_set::get_hash_ref_fn and raw_hash_set::get_alloc_ref_fn for the
// empty class cases.
void* GetRefForEmptyClass(CommonFields& common);
// Given the hash of a value not currently in the table and the first empty
// slot in the probe sequence, finds a viable slot index to insert it at.
//
// In case there's no space left, the table can be resized or rehashed
// (for tables with deleted slots, see FindInsertPositionWithGrowthOrRehash).
//
// In the case of absence of deleted slots and positive growth_left, the element
// can be inserted in the provided `target` position.
//
// When the table has deleted slots (according to GrowthInfo), the target
// position will be searched one more time using `find_first_non_full`.
//
// REQUIRES: Table is not SOO.
// REQUIRES: At least one non-full slot available.
// REQUIRES: `target` is a valid empty position to insert.
size_t PrepareInsertNonSoo(CommonFields& common, const PolicyFunctions& policy,
size_t hash, FindInfo target);
// A SwissTable.
//
// Policy: a policy defines how to perform different operations on
// the slots of the hashtable (see hash_policy_traits.h for the full interface
// of policy).
//
// Hash: a (possibly polymorphic) functor that hashes keys of the hashtable. The
// functor should accept a key and return size_t as hash. For best performance
// it is important that the hash function provides high entropy across all bits
// of the hash.
//
// Eq: a (possibly polymorphic) functor that compares two keys for equality. It
// should accept two (of possibly different type) keys and return a bool: true
// if they are equal, false if they are not. If two keys compare equal, then
// their hash values as defined by Hash MUST be equal.
//
// Allocator: an Allocator
// [https://en.cppreference.com/w/cpp/named_req/Allocator] with which
// the storage of the hashtable will be allocated and the elements will be
// constructed and destroyed.
template <class Policy, class Hash, class Eq, class Alloc>
class raw_hash_set {
using PolicyTraits = hash_policy_traits<Policy>;
using KeyArgImpl =
KeyArg<IsTransparent<Eq>::value && IsTransparent<Hash>::value>;
public:
using init_type = typename PolicyTraits::init_type;
using key_type = typename PolicyTraits::key_type;
using allocator_type = Alloc;
using size_type = size_t;
using difference_type = ptrdiff_t;
using hasher = Hash;
using key_equal = Eq;
using policy_type = Policy;
using value_type = typename PolicyTraits::value_type;
using reference = value_type&;
using const_reference = const value_type&;
using pointer = typename absl::allocator_traits<
allocator_type>::template rebind_traits<value_type>::pointer;
using const_pointer = typename absl::allocator_traits<
allocator_type>::template rebind_traits<value_type>::const_pointer;
private:
// Alias used for heterogeneous lookup functions.
// `key_arg<K>` evaluates to `K` when the functors are transparent and to
// `key_type` otherwise. It permits template argument deduction on `K` for the
// transparent case.
template <class K>
using key_arg = typename KeyArgImpl::template type<K, key_type>;
using slot_type = typename PolicyTraits::slot_type;
// TODO(b/289225379): we could add extra SOO space inside raw_hash_set
// after CommonFields to allow inlining larger slot_types (e.g. std::string),
// but it's a bit complicated if we want to support incomplete mapped_type in
// flat_hash_map. We could potentially do this for flat_hash_set and for an
// allowlist of `mapped_type`s of flat_hash_map that includes e.g. arithmetic
// types, strings, cords, and pairs/tuples of allowlisted types.
constexpr static bool SooEnabled() {
return PolicyTraits::soo_enabled() &&
sizeof(slot_type) <= sizeof(HeapOrSoo) &&
alignof(slot_type) <= alignof(HeapOrSoo);
}
constexpr static size_t DefaultCapacity() {
return SooEnabled() ? SooCapacity() : 0;
}
// Whether `size` fits in the SOO capacity of this table.
bool fits_in_soo(size_t size) const {
return SooEnabled() && size <= SooCapacity();
}
// Whether this table is in SOO mode or non-SOO mode.
bool is_soo() const { return fits_in_soo(capacity()); }
bool is_full_soo() const { return is_soo() && !empty(); }
// Give an early error when key_type is not hashable/eq.
auto KeyTypeCanBeHashed(const Hash& h, const key_type& k) -> decltype(h(k));
auto KeyTypeCanBeEq(const Eq& eq, const key_type& k) -> decltype(eq(k, k));
using AllocTraits = absl::allocator_traits<allocator_type>;
using SlotAlloc = typename absl::allocator_traits<
allocator_type>::template rebind_alloc<slot_type>;
// People are often sloppy with the exact type of their allocator (sometimes
// it has an extra const or is missing the pair, but rebinds made it work
// anyway).
using CharAlloc =
typename absl::allocator_traits<Alloc>::template rebind_alloc<char>;
using SlotAllocTraits = typename absl::allocator_traits<
allocator_type>::template rebind_traits<slot_type>;
static_assert(std::is_lvalue_reference<reference>::value,
"Policy::element() must return a reference");
// An enabler for insert(T&&): T must be convertible to init_type or be the
// same as [cv] value_type [ref].
template <class T>
using Insertable = absl::disjunction<
std::is_same<absl::remove_cvref_t<reference>, absl::remove_cvref_t<T>>,
std::is_convertible<T, init_type>>;
template <class T>
using IsNotBitField = std::is_pointer<T*>;
// RequiresNotInit is a workaround for gcc prior to 7.1.
// See https://godbolt.org/g/Y4xsUh.
template <class T>
using RequiresNotInit =
typename std::enable_if<!std::is_same<T, init_type>::value, int>::type;
template <class... Ts>
using IsDecomposable = IsDecomposable<void, PolicyTraits, Hash, Eq, Ts...>;
template <class T>
using IsDecomposableAndInsertable =
IsDecomposable<std::enable_if_t<Insertable<T>::value, T>>;
// Evaluates to true if an assignment from the given type would require the
// source object to remain alive for the life of the element.
template <class U>
using IsLifetimeBoundAssignmentFrom = std::conditional_t<
policy_trait_element_is_owner<Policy>::value, std::false_type,
type_traits_internal::IsLifetimeBoundAssignment<init_type, U>>;
public:
static_assert(std::is_same<pointer, value_type*>::value,
"Allocators with custom pointer types are not supported");
static_assert(std::is_same<const_pointer, const value_type*>::value,
"Allocators with custom pointer types are not supported");
class iterator : private HashSetIteratorGenerationInfo {
friend class raw_hash_set;
friend struct HashtableFreeFunctionsAccess;
public:
using iterator_category = std::forward_iterator_tag;
using value_type = typename raw_hash_set::value_type;
using reference =
absl::conditional_t<PolicyTraits::constant_iterators::value,
const value_type&, value_type&>;
using pointer = absl::remove_reference_t<reference>*;
using difference_type = typename raw_hash_set::difference_type;
iterator() {}
// PRECONDITION: not an end() iterator.
reference operator*() const {
AssertIsFull(ctrl_, generation(), generation_ptr(), "operator*()");
return unchecked_deref();
}
// PRECONDITION: not an end() iterator.
pointer operator->() const {
AssertIsFull(ctrl_, generation(), generation_ptr(), "operator->");
return &operator*();
}
// PRECONDITION: not an end() iterator.
iterator& operator++() {
AssertIsFull(ctrl_, generation(), generation_ptr(), "operator++");
++ctrl_;
++slot_;
skip_empty_or_deleted();
if (ABSL_PREDICT_FALSE(*ctrl_ == ctrl_t::kSentinel)) ctrl_ = nullptr;
return *this;
}
// PRECONDITION: not an end() iterator.
iterator operator++(int) {
auto tmp = *this;
++*this;
return tmp;
}
friend bool operator==(const iterator& a, const iterator& b) {
AssertIsValidForComparison(a.ctrl_, a.generation(), a.generation_ptr());
AssertIsValidForComparison(b.ctrl_, b.generation(), b.generation_ptr());
AssertSameContainer(a.ctrl_, b.ctrl_, a.slot_, b.slot_,
a.generation_ptr(), b.generation_ptr());
return a.ctrl_ == b.ctrl_;
}
friend bool operator!=(const iterator& a, const iterator& b) {
return !(a == b);
}
private:
iterator(ctrl_t* ctrl, slot_type* slot,
const GenerationType* generation_ptr)
: HashSetIteratorGenerationInfo(generation_ptr),
ctrl_(ctrl),
slot_(slot) {
// This assumption helps the compiler know that any non-end iterator is
// not equal to any end iterator.
ABSL_ASSUME(ctrl != nullptr);
}
// This constructor is used in begin() to avoid an MSan
// use-of-uninitialized-value error. Delegating from this constructor to
// the previous one doesn't avoid the error.
iterator(ctrl_t* ctrl, MaybeInitializedPtr slot,
const GenerationType* generation_ptr)
: HashSetIteratorGenerationInfo(generation_ptr),
ctrl_(ctrl),
slot_(to_slot(slot.get())) {
// This assumption helps the compiler know that any non-end iterator is
// not equal to any end iterator.
ABSL_ASSUME(ctrl != nullptr);
}
// For end() iterators.
explicit iterator(const GenerationType* generation_ptr)
: HashSetIteratorGenerationInfo(generation_ptr), ctrl_(nullptr) {}
// Fixes up `ctrl_` to point to a full or sentinel by advancing `ctrl_` and
// `slot_` until they reach one.
void skip_empty_or_deleted() {
while (IsEmptyOrDeleted(*ctrl_)) {
uint32_t shift =
GroupFullEmptyOrDeleted{ctrl_}.CountLeadingEmptyOrDeleted();
ctrl_ += shift;
slot_ += shift;
}
}
ctrl_t* control() const { return ctrl_; }
slot_type* slot() const { return slot_; }
// We use EmptyGroup() for default-constructed iterators so that they can
// be distinguished from end iterators, which have nullptr ctrl_.
ctrl_t* ctrl_ = EmptyGroup();
// To avoid uninitialized member warnings, put slot_ in an anonymous union.
// The member is not initialized on singleton and end iterators.
union {
slot_type* slot_;
};
// An equality check which skips ABSL Hardening iterator invalidation
// checks.
// Should be used when the lifetimes of the iterators are well-enough
// understood to prove that they cannot be invalid.
bool unchecked_equals(const iterator& b) { return ctrl_ == b.control(); }
// Dereferences the iterator without ABSL Hardening iterator invalidation
// checks.
reference unchecked_deref() const { return PolicyTraits::element(slot_); }
};
class const_iterator {
friend class raw_hash_set;
template <class Container, typename Enabler>
friend struct absl::container_internal::hashtable_debug_internal::
HashtableDebugAccess;
public:
using iterator_category = typename iterator::iterator_category;
using value_type = typename raw_hash_set::value_type;
using reference = typename raw_hash_set::const_reference;
using pointer = typename raw_hash_set::const_pointer;
using difference_type = typename raw_hash_set::difference_type;
const_iterator() = default;
// Implicit construction from iterator.
const_iterator(iterator i) : inner_(std::move(i)) {} // NOLINT
reference operator*() const { return *inner_; }
pointer operator->() const { return inner_.operator->(); }
const_iterator& operator++() {
++inner_;
return *this;
}
const_iterator operator++(int) { return inner_++; }
friend bool operator==(const const_iterator& a, const const_iterator& b) {
return a.inner_ == b.inner_;
}
friend bool operator!=(const const_iterator& a, const const_iterator& b) {
return !(a == b);
}
private:
const_iterator(const ctrl_t* ctrl, const slot_type* slot,
const GenerationType* gen)
: inner_(const_cast<ctrl_t*>(ctrl), const_cast<slot_type*>(slot), gen) {
}
ctrl_t* control() const { return inner_.control(); }
slot_type* slot() const { return inner_.slot(); }
iterator inner_;
bool unchecked_equals(const const_iterator& b) {
return inner_.unchecked_equals(b.inner_);
}
};
using node_type = node_handle<Policy, hash_policy_traits<Policy>, Alloc>;
using insert_return_type = InsertReturnType<iterator, node_type>;
// Note: can't use `= default` due to non-default noexcept (causes
// problems for some compilers). NOLINTNEXTLINE
raw_hash_set() noexcept(
std::is_nothrow_default_constructible<hasher>::value &&
std::is_nothrow_default_constructible<key_equal>::value &&
std::is_nothrow_default_constructible<allocator_type>::value) {}
ABSL_ATTRIBUTE_NOINLINE explicit raw_hash_set(
size_t bucket_count, const hasher& hash = hasher(),
const key_equal& eq = key_equal(),
const allocator_type& alloc = allocator_type())
: settings_(CommonFields::CreateDefault<SooEnabled()>(), hash, eq,
alloc) {
if (bucket_count > DefaultCapacity()) {
ReserveEmptyNonAllocatedTableToFitBucketCount(
common(), GetPolicyFunctions(), bucket_count);
}
}
raw_hash_set(size_t bucket_count, const hasher& hash,
const allocator_type& alloc)
: raw_hash_set(bucket_count, hash, key_equal(), alloc) {}
raw_hash_set(size_t bucket_count, const allocator_type& alloc)
: raw_hash_set(bucket_count, hasher(), key_equal(), alloc) {}
explicit raw_hash_set(const allocator_type& alloc)
: raw_hash_set(0, hasher(), key_equal(), alloc) {}
template <class InputIter>
raw_hash_set(InputIter first, InputIter last, size_t bucket_count = 0,
const hasher& hash = hasher(), const key_equal& eq = key_equal(),
const allocator_type& alloc = allocator_type())
: raw_hash_set(SelectBucketCountForIterRange(first, last, bucket_count),
hash, eq, alloc) {
insert(first, last);
}
template <class InputIter>
raw_hash_set(InputIter first, InputIter last, size_t bucket_count,
const hasher& hash, const allocator_type& alloc)
: raw_hash_set(first, last, bucket_count, hash, key_equal(), alloc) {}
template <class InputIter>
raw_hash_set(InputIter first, InputIter last, size_t bucket_count,
const allocator_type& alloc)
: raw_hash_set(first, last, bucket_count, hasher(), key_equal(), alloc) {}
template <class InputIter>
raw_hash_set(InputIter first, InputIter last, const allocator_type& alloc)
: raw_hash_set(first, last, 0, hasher(), key_equal(), alloc) {}
// Instead of accepting std::initializer_list<value_type> as the first
// argument like std::unordered_set<value_type> does, we have two overloads
// that accept std::initializer_list<T> and std::initializer_list<init_type>.
// This is advantageous for performance.
//
// // Turns {"abc", "def"} into std::initializer_list<std::string>, then
// // copies the strings into the set.
// std::unordered_set<std::string> s = {"abc", "def"};
//
// // Turns {"abc", "def"} into std::initializer_list<const char*>, then
// // copies the strings into the set.
// absl::flat_hash_set<std::string> s = {"abc", "def"};
//
// The same trick is used in insert().
//
// The enabler is necessary to prevent this constructor from triggering where
// the copy constructor is meant to be called.
//
// absl::flat_hash_set<int> a, b{a};
//
// RequiresNotInit<T> is a workaround for gcc prior to 7.1.
template <class T, RequiresNotInit<T> = 0,
std::enable_if_t<Insertable<T>::value, int> = 0>
raw_hash_set(std::initializer_list<T> init, size_t bucket_count = 0,
const hasher& hash = hasher(), const key_equal& eq = key_equal(),
const allocator_type& alloc = allocator_type())
: raw_hash_set(init.begin(), init.end(), bucket_count, hash, eq, alloc) {}
raw_hash_set(std::initializer_list<init_type> init, size_t bucket_count = 0,
const hasher& hash = hasher(), const key_equal& eq = key_equal(),
const allocator_type& alloc = allocator_type())
: raw_hash_set(init.begin(), init.end(), bucket_count, hash, eq, alloc) {}
template <class T, RequiresNotInit<T> = 0,
std::enable_if_t<Insertable<T>::value, int> = 0>
raw_hash_set(std::initializer_list<T> init, size_t bucket_count,
const hasher& hash, const allocator_type& alloc)
: raw_hash_set(init, bucket_count, hash, key_equal(), alloc) {}
raw_hash_set(std::initializer_list<init_type> init, size_t bucket_count,
const hasher& hash, const allocator_type& alloc)
: raw_hash_set(init, bucket_count, hash, key_equal(), alloc) {}
template <class T, RequiresNotInit<T> = 0,
std::enable_if_t<Insertable<T>::value, int> = 0>
raw_hash_set(std::initializer_list<T> init, size_t bucket_count,
const allocator_type& alloc)
: raw_hash_set(init, bucket_count, hasher(), key_equal(), alloc) {}
raw_hash_set(std::initializer_list<init_type> init, size_t bucket_count,
const allocator_type& alloc)
: raw_hash_set(init, bucket_count, hasher(), key_equal(), alloc) {}
template <class T, RequiresNotInit<T> = 0,
std::enable_if_t<Insertable<T>::value, int> = 0>
raw_hash_set(std::initializer_list<T> init, const allocator_type& alloc)
: raw_hash_set(init, 0, hasher(), key_equal(), alloc) {}
raw_hash_set(std::initializer_list<init_type> init,
const allocator_type& alloc)
: raw_hash_set(init, 0, hasher(), key_equal(), alloc) {}
raw_hash_set(const raw_hash_set& that)
: raw_hash_set(that, AllocTraits::select_on_container_copy_construction(
allocator_type(that.char_alloc_ref()))) {}
raw_hash_set(const raw_hash_set& that, const allocator_type& a)
: raw_hash_set(GrowthToLowerboundCapacity(that.size()), that.hash_ref(),
that.eq_ref(), a) {
that.AssertNotDebugCapacity();
const size_t size = that.size();
if (size == 0) {
return;
}
// We don't use `that.is_soo()` here because `that` can have non-SOO
// capacity but have a size that fits into SOO capacity.
if (fits_in_soo(size)) {
ABSL_SWISSTABLE_ASSERT(size == 1);
common().set_full_soo();
emplace_at(soo_iterator(), *that.begin());
if (should_sample_soo()) {
GrowFullSooTableToNextCapacityForceSampling(common(),
GetPolicyFunctions());
}
return;
}
ABSL_SWISSTABLE_ASSERT(!that.is_soo());
const size_t cap = capacity();
// Note about single group tables:
// 1. It is correct to have any order of elements.
// 2. Order has to be non deterministic.
// 3. We are assigning elements with arbitrary `shift` starting from
// `capacity + shift` position.
// 4. `shift` must be coprime with `capacity + 1` in order to be able to use
// modular arithmetic to traverse all positions, instead if cycling
// through a subset of positions. Odd numbers are coprime with any
// `capacity + 1` (2^N).
size_t offset = cap;
const size_t shift =
is_single_group(cap) ? (common().seed().seed() | 1) : 0;
IterateOverFullSlots(
that.common(), sizeof(slot_type),
[&](const ctrl_t* that_ctrl, void* that_slot_void) {
slot_type* that_slot = static_cast<slot_type*>(that_slot_void);
if (shift == 0) {
// Big tables case. Position must be searched via probing.
// The table is guaranteed to be empty, so we can do faster than
// a full `insert`.
const size_t hash = PolicyTraits::apply(
HashElement{hash_ref()}, PolicyTraits::element(that_slot));
FindInfo target = find_first_non_full_outofline(common(), hash);
infoz().RecordInsert(hash, target.probe_length);
offset = target.offset;
} else {
// Small tables case. Next position is computed via shift.
offset = (offset + shift) & cap;
}
const h2_t h2 = static_cast<h2_t>(*that_ctrl);
ABSL_SWISSTABLE_ASSERT( // We rely that hash is not changed for small
// tables.
H2(PolicyTraits::apply(HashElement{hash_ref()},
PolicyTraits::element(that_slot))) == h2 &&
"hash function value changed unexpectedly during the copy");
SetCtrl(common(), offset, h2, sizeof(slot_type));
emplace_at(iterator_at(offset), PolicyTraits::element(that_slot));
common().maybe_increment_generation_on_insert();
});
if (shift != 0) {
// On small table copy we do not record individual inserts.
// RecordInsert requires hash, but it is unknown for small tables.
infoz().RecordStorageChanged(size, cap);
}
common().increment_size(size);
growth_info().OverwriteManyEmptyAsFull(size);
}
ABSL_ATTRIBUTE_NOINLINE raw_hash_set(raw_hash_set&& that) noexcept(
std::is_nothrow_copy_constructible<hasher>::value &&
std::is_nothrow_copy_constructible<key_equal>::value &&
std::is_nothrow_copy_constructible<allocator_type>::value)
: // Hash, equality and allocator are copied instead of moved because
// `that` must be left valid. If Hash is std::function<Key>, moving it
// would create a nullptr functor that cannot be called.
// Note: we avoid using exchange for better generated code.
settings_(PolicyTraits::transfer_uses_memcpy() || !that.is_full_soo()
? std::move(that.common())
: CommonFields{full_soo_tag_t{}},
that.hash_ref(), that.eq_ref(), that.char_alloc_ref()) {
if (!PolicyTraits::transfer_uses_memcpy() && that.is_full_soo()) {
transfer(soo_slot(), that.soo_slot());
}
that.common() = CommonFields::CreateDefault<SooEnabled()>();
annotate_for_bug_detection_on_move(that);
}
raw_hash_set(raw_hash_set&& that, const allocator_type& a)
: settings_(CommonFields::CreateDefault<SooEnabled()>(), that.hash_ref(),
that.eq_ref(), a) {
if (CharAlloc(a) == that.char_alloc_ref()) {
swap_common(that);
annotate_for_bug_detection_on_move(that);
} else {
move_elements_allocs_unequal(std::move(that));
}
}
raw_hash_set& operator=(const raw_hash_set& that) {
that.AssertNotDebugCapacity();
if (ABSL_PREDICT_FALSE(this == &that)) return *this;
constexpr bool propagate_alloc =
AllocTraits::propagate_on_container_copy_assignment::value;
// TODO(ezb): maybe avoid allocating a new backing array if this->capacity()
// is an exact match for that.size(). If this->capacity() is too big, then
// it would make iteration very slow to reuse the allocation. Maybe we can
// do the same heuristic as clear() and reuse if it's small enough.
allocator_type alloc(propagate_alloc ? that.char_alloc_ref()
: char_alloc_ref());
raw_hash_set tmp(that, alloc);
// NOLINTNEXTLINE: not returning *this for performance.
return assign_impl<propagate_alloc>(std::move(tmp));
}
raw_hash_set& operator=(raw_hash_set&& that) noexcept(
absl::allocator_traits<allocator_type>::is_always_equal::value &&
std::is_nothrow_move_assignable<hasher>::value &&
std::is_nothrow_move_assignable<key_equal>::value) {
// TODO(sbenza): We should only use the operations from the noexcept clause
// to make sure we actually adhere to that contract.
// NOLINTNEXTLINE: not returning *this for performance.
return move_assign(
std::move(that),
typename AllocTraits::propagate_on_container_move_assignment());
}
~raw_hash_set() {
destructor_impl();
if constexpr (SwisstableAssertAccessToDestroyedTable()) {
common().set_capacity(InvalidCapacity::kDestroyed);
}
}
iterator begin() ABSL_ATTRIBUTE_LIFETIME_BOUND {
if (ABSL_PREDICT_FALSE(empty())) return end();
if (is_soo()) return soo_iterator();
iterator it = {control(), common().slots_union(),
common().generation_ptr()};
it.skip_empty_or_deleted();
ABSL_SWISSTABLE_ASSERT(IsFull(*it.control()));
return it;
}
iterator end() ABSL_ATTRIBUTE_LIFETIME_BOUND {
AssertNotDebugCapacity();
return iterator(common().generation_ptr());
}
const_iterator begin() const ABSL_ATTRIBUTE_LIFETIME_BOUND {
return const_cast<raw_hash_set*>(this)->begin();
}
const_iterator end() const ABSL_ATTRIBUTE_LIFETIME_BOUND {
return const_cast<raw_hash_set*>(this)->end();
}
const_iterator cbegin() const ABSL_ATTRIBUTE_LIFETIME_BOUND {
return begin();
}
const_iterator cend() const ABSL_ATTRIBUTE_LIFETIME_BOUND { return end(); }
bool empty() const { return !size(); }
size_t size() const {
AssertNotDebugCapacity();
return common().size();
}
size_t capacity() const {
const size_t cap = common().capacity();
// Compiler complains when using functions in ASSUME so use local variable.
ABSL_ATTRIBUTE_UNUSED static constexpr size_t kDefaultCapacity =
DefaultCapacity();
ABSL_ASSUME(cap >= kDefaultCapacity);
return cap;
}
size_t max_size() const { return MaxValidSize(sizeof(slot_type)); }
ABSL_ATTRIBUTE_REINITIALIZES void clear() {
if (SwisstableGenerationsEnabled() &&
capacity() >= InvalidCapacity::kMovedFrom) {
common().set_capacity(DefaultCapacity());
}
AssertNotDebugCapacity();
// Iterating over this container is O(bucket_count()). When bucket_count()
// is much greater than size(), iteration becomes prohibitively expensive.
// For clear() it is more important to reuse the allocated array when the
// container is small because allocation takes comparatively long time
// compared to destruction of the elements of the container. So we pick the
// largest bucket_count() threshold for which iteration is still fast and
// past that we simply deallocate the array.
const size_t cap = capacity();
if (cap == 0) {
// Already guaranteed to be empty; so nothing to do.
} else if (is_soo()) {
if (!empty()) destroy(soo_slot());
common().set_empty_soo();
} else {
destroy_slots();
clear_backing_array(/*reuse=*/cap < 128);
}
common().set_reserved_growth(0);
common().set_reservation_size(0);
}
// This overload kicks in when the argument is an rvalue of insertable and
// decomposable type other than init_type.
//
// flat_hash_map<std::string, int> m;
// m.insert(std::make_pair("abc", 42));
template <class T,
int = std::enable_if_t<IsDecomposableAndInsertable<T>::value &&
IsNotBitField<T>::value &&
!IsLifetimeBoundAssignmentFrom<T>::value,
int>()>
std::pair<iterator, bool> insert(T&& value) ABSL_ATTRIBUTE_LIFETIME_BOUND {
return emplace(std::forward<T>(value));
}
template <class T, int&...,
std::enable_if_t<IsDecomposableAndInsertable<T>::value &&
IsNotBitField<T>::value &&
IsLifetimeBoundAssignmentFrom<T>::value,
int> = 0>
std::pair<iterator, bool> insert(
T&& value ABSL_INTERNAL_ATTRIBUTE_CAPTURED_BY(this))
ABSL_ATTRIBUTE_LIFETIME_BOUND {
return this->template insert<T, 0>(std::forward<T>(value));
}
// This overload kicks in when the argument is a bitfield or an lvalue of
// insertable and decomposable type.
//
// union { int n : 1; };
// flat_hash_set<int> s;
// s.insert(n);
//
// flat_hash_set<std::string> s;
// const char* p = "hello";
// s.insert(p);
//
template <class T, int = std::enable_if_t<
IsDecomposableAndInsertable<const T&>::value &&
!IsLifetimeBoundAssignmentFrom<const T&>::value,
int>()>
std::pair<iterator, bool> insert(const T& value)
ABSL_ATTRIBUTE_LIFETIME_BOUND {
return emplace(value);
}
template <class T, int&...,
std::enable_if_t<IsDecomposableAndInsertable<const T&>::value &&
IsLifetimeBoundAssignmentFrom<const T&>::value,
int> = 0>
std::pair<iterator, bool> insert(
const T& value ABSL_INTERNAL_ATTRIBUTE_CAPTURED_BY(this))
ABSL_ATTRIBUTE_LIFETIME_BOUND {
return this->template insert<T, 0>(value);
}
// This overload kicks in when the argument is an rvalue of init_type. Its
// purpose is to handle brace-init-list arguments.
//
// flat_hash_map<std::string, int> s;
// s.insert({"abc", 42});
std::pair<iterator, bool> insert(init_type&& value)
ABSL_ATTRIBUTE_LIFETIME_BOUND
#if __cplusplus >= 202002L
requires(!IsLifetimeBoundAssignmentFrom<init_type>::value)
#endif
{
return emplace(std::move(value));
}
#if __cplusplus >= 202002L
std::pair<iterator, bool> insert(
init_type&& value ABSL_INTERNAL_ATTRIBUTE_CAPTURED_BY(this))
ABSL_ATTRIBUTE_LIFETIME_BOUND
requires(IsLifetimeBoundAssignmentFrom<init_type>::value)
{
return emplace(std::move(value));
}
#endif
template <class T,
int = std::enable_if_t<IsDecomposableAndInsertable<T>::value &&
IsNotBitField<T>::value &&
!IsLifetimeBoundAssignmentFrom<T>::value,
int>()>
iterator insert(const_iterator, T&& value) ABSL_ATTRIBUTE_LIFETIME_BOUND {
return insert(std::forward<T>(value)).first;
}
template <class T, int&...,
std::enable_if_t<IsDecomposableAndInsertable<T>::value &&
IsNotBitField<T>::value &&
IsLifetimeBoundAssignmentFrom<T>::value,
int> = 0>
iterator insert(const_iterator hint,
T&& value ABSL_INTERNAL_ATTRIBUTE_CAPTURED_BY(this))
ABSL_ATTRIBUTE_LIFETIME_BOUND {
return this->template insert<T, 0>(hint, std::forward<T>(value));
}
template <class T, std::enable_if_t<
IsDecomposableAndInsertable<const T&>::value, int> = 0>
iterator insert(const_iterator,
const T& value) ABSL_ATTRIBUTE_LIFETIME_BOUND {
return insert(value).first;
}
iterator insert(const_iterator,
init_type&& value) ABSL_ATTRIBUTE_LIFETIME_BOUND {
return insert(std::move(value)).first;
}
template <class InputIt>
void insert(InputIt first, InputIt last) {
for (; first != last; ++first) emplace(*first);
}
template <class T, RequiresNotInit<T> = 0,
std::enable_if_t<Insertable<const T&>::value, int> = 0>
void insert(std::initializer_list<T> ilist) {
insert(ilist.begin(), ilist.end());
}
void insert(std::initializer_list<init_type> ilist) {
insert(ilist.begin(), ilist.end());
}
insert_return_type insert(node_type&& node) ABSL_ATTRIBUTE_LIFETIME_BOUND {
if (!node) return {end(), false, node_type()};
const auto& elem = PolicyTraits::element(CommonAccess::GetSlot(node));
auto res = PolicyTraits::apply(
InsertSlot<false>{*this, std::move(*CommonAccess::GetSlot(node))},
elem);
if (res.second) {
CommonAccess::Reset(&node);
return {res.first, true, node_type()};
} else {
return {res.first, false, std::move(node)};
}
}
iterator insert(const_iterator,
node_type&& node) ABSL_ATTRIBUTE_LIFETIME_BOUND {
auto res = insert(std::move(node));
node = std::move(res.node);
return res.position;
}
// This overload kicks in if we can deduce the key from args. This enables us
// to avoid constructing value_type if an entry with the same key already
// exists.
//
// For example:
//
// flat_hash_map<std::string, std::string> m = {{"abc", "def"}};
// // Creates no std::string copies and makes no heap allocations.
// m.emplace("abc", "xyz");
template <class... Args,
std::enable_if_t<IsDecomposable<Args...>::value, int> = 0>
std::pair<iterator, bool> emplace(Args&&... args)
ABSL_ATTRIBUTE_LIFETIME_BOUND {
return PolicyTraits::apply(EmplaceDecomposable{*this},
std::forward<Args>(args)...);
}
// This overload kicks in if we cannot deduce the key from args. It constructs
// value_type unconditionally and then either moves it into the table or
// destroys.
template <class... Args,
std::enable_if_t<!IsDecomposable<Args...>::value, int> = 0>
std::pair<iterator, bool> emplace(Args&&... args)
ABSL_ATTRIBUTE_LIFETIME_BOUND {
alignas(slot_type) unsigned char raw[sizeof(slot_type)];
slot_type* slot = to_slot(&raw);
construct(slot, std::forward<Args>(args)...);
const auto& elem = PolicyTraits::element(slot);
return PolicyTraits::apply(InsertSlot<true>{*this, std::move(*slot)}, elem);
}
template <class... Args>
iterator emplace_hint(const_iterator,
Args&&... args) ABSL_ATTRIBUTE_LIFETIME_BOUND {
return emplace(std::forward<Args>(args)...).first;
}
// Extension API: support for lazy emplace.
//
// Looks up key in the table. If found, returns the iterator to the element.
// Otherwise calls `f` with one argument of type `raw_hash_set::constructor`,
// and returns an iterator to the new element.
//
// `f` must abide by several restrictions:
// - it MUST call `raw_hash_set::constructor` with arguments as if a
// `raw_hash_set::value_type` is constructed,
// - it MUST NOT access the container before the call to
// `raw_hash_set::constructor`, and
// - it MUST NOT erase the lazily emplaced element.
// Doing any of these is undefined behavior.
//
// For example:
//
// std::unordered_set<ArenaString> s;
// // Makes ArenaStr even if "abc" is in the map.
// s.insert(ArenaString(&arena, "abc"));
//
// flat_hash_set<ArenaStr> s;
// // Makes ArenaStr only if "abc" is not in the map.
// s.lazy_emplace("abc", [&](const constructor& ctor) {
// ctor(&arena, "abc");
// });
//
// WARNING: This API is currently experimental. If there is a way to implement
// the same thing with the rest of the API, prefer that.
class constructor {
friend class raw_hash_set;
public:
template <class... Args>
void operator()(Args&&... args) const {
ABSL_SWISSTABLE_ASSERT(*slot_);
PolicyTraits::construct(alloc_, *slot_, std::forward<Args>(args)...);
*slot_ = nullptr;
}
private:
constructor(allocator_type* a, slot_type** slot) : alloc_(a), slot_(slot) {}
allocator_type* alloc_;
slot_type** slot_;
};
template <class K = key_type, class F>
iterator lazy_emplace(const key_arg<K>& key,
F&& f) ABSL_ATTRIBUTE_LIFETIME_BOUND {
auto res = find_or_prepare_insert(key);
if (res.second) {
slot_type* slot = res.first.slot();
allocator_type alloc(char_alloc_ref());
std::forward<F>(f)(constructor(&alloc, &slot));
ABSL_SWISSTABLE_ASSERT(!slot);
}
return res.first;
}
// Extension API: support for heterogeneous keys.
//
// std::unordered_set<std::string> s;
// // Turns "abc" into std::string.
// s.erase("abc");
//
// flat_hash_set<std::string> s;
// // Uses "abc" directly without copying it into std::string.
// s.erase("abc");
template <class K = key_type>
size_type erase(const key_arg<K>& key) {
auto it = find(key);
if (it == end()) return 0;
erase(it);
return 1;
}
// Erases the element pointed to by `it`. Unlike `std::unordered_set::erase`,
// this method returns void to reduce algorithmic complexity to O(1). The
// iterator is invalidated so any increment should be done before calling
// erase (e.g. `erase(it++)`).
void erase(const_iterator cit) { erase(cit.inner_); }
// This overload is necessary because otherwise erase<K>(const K&) would be
// a better match if non-const iterator is passed as an argument.
void erase(iterator it) {
AssertNotDebugCapacity();
AssertIsFull(it.control(), it.generation(), it.generation_ptr(), "erase()");
destroy(it.slot());
if (is_soo()) {
common().set_empty_soo();
} else {
erase_meta_only(it);
}
}
iterator erase(const_iterator first,
const_iterator last) ABSL_ATTRIBUTE_LIFETIME_BOUND {
AssertNotDebugCapacity();
// We check for empty first because clear_backing_array requires that
// capacity() > 0 as a precondition.
if (empty()) return end();
if (first == last) return last.inner_;
if (is_soo()) {
destroy(soo_slot());
common().set_empty_soo();
return end();
}
if (first == begin() && last == end()) {
// TODO(ezb): we access control bytes in destroy_slots so it could make
// sense to combine destroy_slots and clear_backing_array to avoid cache
// misses when the table is large. Note that we also do this in clear().
destroy_slots();
clear_backing_array(/*reuse=*/true);
common().set_reserved_growth(common().reservation_size());
return end();
}
while (first != last) {
erase(first++);
}
return last.inner_;
}
// Moves elements from `src` into `this`.
// If the element already exists in `this`, it is left unmodified in `src`.
template <typename H, typename E>
void merge(raw_hash_set<Policy, H, E, Alloc>& src) { // NOLINT
AssertNotDebugCapacity();
src.AssertNotDebugCapacity();
assert(this != &src);
// Returns whether insertion took place.
const auto insert_slot = [this](slot_type* src_slot) {
return PolicyTraits::apply(InsertSlot<false>{*this, std::move(*src_slot)},
PolicyTraits::element(src_slot))
.second;
};
if (src.is_soo()) {
if (src.empty()) return;
if (insert_slot(src.soo_slot())) src.common().set_empty_soo();
return;
}
for (auto it = src.begin(), e = src.end(); it != e;) {
auto next = std::next(it);
if (insert_slot(it.slot())) src.erase_meta_only(it);
it = next;
}
}
template <typename H, typename E>
void merge(raw_hash_set<Policy, H, E, Alloc>&& src) {
merge(src);
}
node_type extract(const_iterator position) {
AssertNotDebugCapacity();
AssertIsFull(position.control(), position.inner_.generation(),
position.inner_.generation_ptr(), "extract()");
allocator_type alloc(char_alloc_ref());
auto node = CommonAccess::Transfer<node_type>(alloc, position.slot());
if (is_soo()) {
common().set_empty_soo();
} else {
erase_meta_only(position);
}
return node;
}
template <class K = key_type,
std::enable_if_t<!std::is_same<K, iterator>::value, int> = 0>
node_type extract(const key_arg<K>& key) {
auto it = find(key);
return it == end() ? node_type() : extract(const_iterator{it});
}
void swap(raw_hash_set& that) noexcept(
IsNoThrowSwappable<hasher>() && IsNoThrowSwappable<key_equal>() &&
IsNoThrowSwappable<allocator_type>(
typename AllocTraits::propagate_on_container_swap{})) {
AssertNotDebugCapacity();
that.AssertNotDebugCapacity();
using std::swap;
swap_common(that);
swap(hash_ref(), that.hash_ref());
swap(eq_ref(), that.eq_ref());
SwapAlloc(char_alloc_ref(), that.char_alloc_ref(),
typename AllocTraits::propagate_on_container_swap{});
}
void rehash(size_t n) { Rehash(common(), GetPolicyFunctions(), n); }
void reserve(size_t n) {
const size_t cap = capacity();
if (ABSL_PREDICT_TRUE(cap > DefaultCapacity() ||
// !SooEnabled() implies empty(), so we can skip the
// check for optimization.
(SooEnabled() && !empty()))) {
ReserveAllocatedTable(common(), GetPolicyFunctions(), n);
} else {
if (ABSL_PREDICT_TRUE(n > DefaultCapacity())) {
ReserveEmptyNonAllocatedTableToFitNewSize(common(),
GetPolicyFunctions(), n);
}
}
}
// Extension API: support for heterogeneous keys.
//
// std::unordered_set<std::string> s;
// // Turns "abc" into std::string.
// s.count("abc");
//
// ch_set<std::string> s;
// // Uses "abc" directly without copying it into std::string.
// s.count("abc");
template <class K = key_type>
size_t count(const key_arg<K>& key) const {
return find(key) == end() ? 0 : 1;
}
// Issues CPU prefetch instructions for the memory needed to find or insert
// a key. Like all lookup functions, this support heterogeneous keys.
//
// NOTE: This is a very low level operation and should not be used without
// specific benchmarks indicating its importance.
template <class K = key_type>
void prefetch(const key_arg<K>& key) const {
if (capacity() == DefaultCapacity()) return;
(void)key;
// Avoid probing if we won't be able to prefetch the addresses received.
#ifdef ABSL_HAVE_PREFETCH
prefetch_heap_block();
auto seq = probe(common(), hash_ref()(key));
PrefetchToLocalCache(control() + seq.offset());
PrefetchToLocalCache(slot_array() + seq.offset());
#endif // ABSL_HAVE_PREFETCH
}
template <class K = key_type>
ABSL_DEPRECATE_AND_INLINE()
iterator find(const key_arg<K>& key,
size_t) ABSL_ATTRIBUTE_LIFETIME_BOUND {
return find(key);
}
// The API of find() has one extension: the type of the key argument doesn't
// have to be key_type. This is so called heterogeneous key support.
template <class K = key_type>
iterator find(const key_arg<K>& key) ABSL_ATTRIBUTE_LIFETIME_BOUND {
AssertOnFind(key);
if (is_soo()) return find_soo(key);
prefetch_heap_block();
return find_non_soo(key, hash_ref()(key));
}
template <class K = key_type>
ABSL_DEPRECATE_AND_INLINE()
const_iterator find(const key_arg<K>& key,
size_t) const ABSL_ATTRIBUTE_LIFETIME_BOUND {
return find(key);
}
template <class K = key_type>
const_iterator find(const key_arg<K>& key) const
ABSL_ATTRIBUTE_LIFETIME_BOUND {
return const_cast<raw_hash_set*>(this)->find(key);
}
template <class K = key_type>
bool contains(const key_arg<K>& key) const {
// Here neither the iterator returned by `find()` nor `end()` can be invalid
// outside of potential thread-safety issues.
// `find()`'s return value is constructed, used, and then destructed
// all in this context.
return !find(key).unchecked_equals(end());
}
template <class K = key_type>
std::pair<iterator, iterator> equal_range(const key_arg<K>& key)
ABSL_ATTRIBUTE_LIFETIME_BOUND {
auto it = find(key);
if (it != end()) return {it, std::next(it)};
return {it, it};
}
template <class K = key_type>
std::pair<const_iterator, const_iterator> equal_range(
const key_arg<K>& key) const ABSL_ATTRIBUTE_LIFETIME_BOUND {
auto it = find(key);
if (it != end()) return {it, std::next(it)};
return {it, it};
}
size_t bucket_count() const { return capacity(); }
float load_factor() const {
return capacity() ? static_cast<double>(size()) / capacity() : 0.0;
}
float max_load_factor() const { return 1.0f; }
void max_load_factor(float) {
// Does nothing.
}
hasher hash_function() const { return hash_ref(); }
key_equal key_eq() const { return eq_ref(); }
allocator_type get_allocator() const {
return allocator_type(char_alloc_ref());
}
friend bool operator==(const raw_hash_set& a, const raw_hash_set& b) {
if (a.size() != b.size()) return false;
const raw_hash_set* outer = &a;
const raw_hash_set* inner = &b;
if (outer->capacity() > inner->capacity()) std::swap(outer, inner);
for (const value_type& elem : *outer) {
auto it = PolicyTraits::apply(FindElement{*inner}, elem);
if (it == inner->end()) return false;
// Note: we used key_equal to check for key equality in FindElement, but
// we may need to do an additional comparison using
// value_type::operator==. E.g. the keys could be equal and the
// mapped_types could be unequal in a map or even in a set, key_equal
// could ignore some fields that aren't ignored by operator==.
static constexpr bool kKeyEqIsValueEq =
std::is_same<key_type, value_type>::value &&
std::is_same<key_equal, hash_default_eq<key_type>>::value;
if (!kKeyEqIsValueEq && !(*it == elem)) return false;
}
return true;
}
friend bool operator!=(const raw_hash_set& a, const raw_hash_set& b) {
return !(a == b);
}
template <typename H>
friend typename std::enable_if<H::template is_hashable<value_type>::value,
H>::type
AbslHashValue(H h, const raw_hash_set& s) {
return H::combine(H::combine_unordered(std::move(h), s.begin(), s.end()),
s.size());
}
friend void swap(raw_hash_set& a,
raw_hash_set& b) noexcept(noexcept(a.swap(b))) {
a.swap(b);
}
private:
template <class Container, typename Enabler>
friend struct absl::container_internal::hashtable_debug_internal::
HashtableDebugAccess;
friend struct absl::container_internal::HashtableFreeFunctionsAccess;
struct FindElement {
template <class K, class... Args>
const_iterator operator()(const K& key, Args&&...) const {
return s.find(key);
}
const raw_hash_set& s;
};
struct HashElement {
template <class K, class... Args>
size_t operator()(const K& key, Args&&...) const {
return h(key);
}
const hasher& h;
};
template <class K1>
struct EqualElement {
template <class K2, class... Args>
bool operator()(const K2& lhs, Args&&...) const {
ABSL_SWISSTABLE_IGNORE_UNINITIALIZED_RETURN(eq(lhs, rhs));
}
const K1& rhs;
const key_equal& eq;
};
struct EmplaceDecomposable {
template <class K, class... Args>
std::pair<iterator, bool> operator()(const K& key, Args&&... args) const {
auto res = s.find_or_prepare_insert(key);
if (res.second) {
s.emplace_at(res.first, std::forward<Args>(args)...);
}
return res;
}
raw_hash_set& s;
};
template <bool do_destroy>
struct InsertSlot {
template <class K, class... Args>
std::pair<iterator, bool> operator()(const K& key, Args&&...) && {
auto res = s.find_or_prepare_insert(key);
if (res.second) {
s.transfer(res.first.slot(), &slot);
} else if (do_destroy) {
s.destroy(&slot);
}
return res;
}
raw_hash_set& s;
// Constructed slot. Either moved into place or destroyed.
slot_type&& slot;
};
template <typename... Args>
inline void construct(slot_type* slot, Args&&... args) {
common().RunWithReentrancyGuard([&] {
allocator_type alloc(char_alloc_ref());
PolicyTraits::construct(&alloc, slot, std::forward<Args>(args)...);
});
}
inline void destroy(slot_type* slot) {
common().RunWithReentrancyGuard([&] {
allocator_type alloc(char_alloc_ref());
PolicyTraits::destroy(&alloc, slot);
});
}
inline void transfer(slot_type* to, slot_type* from) {
common().RunWithReentrancyGuard([&] {
allocator_type alloc(char_alloc_ref());
PolicyTraits::transfer(&alloc, to, from);
});
}
// TODO(b/289225379): consider having a helper class that has the impls for
// SOO functionality.
template <class K = key_type>
iterator find_soo(const key_arg<K>& key) {
ABSL_SWISSTABLE_ASSERT(is_soo());
return empty() || !PolicyTraits::apply(EqualElement<K>{key, eq_ref()},
PolicyTraits::element(soo_slot()))
? end()
: soo_iterator();
}
template <class K = key_type>
iterator find_non_soo(const key_arg<K>& key, size_t hash) {
ABSL_SWISSTABLE_ASSERT(!is_soo());
auto seq = probe(common(), hash);
const ctrl_t* ctrl = control();
while (true) {
Group g{ctrl + seq.offset()};
for (uint32_t i : g.Match(H2(hash))) {
if (ABSL_PREDICT_TRUE(PolicyTraits::apply(
EqualElement<K>{key, eq_ref()},
PolicyTraits::element(slot_array() + seq.offset(i)))))
return iterator_at(seq.offset(i));
}
if (ABSL_PREDICT_TRUE(g.MaskEmpty())) return end();
seq.next();
ABSL_SWISSTABLE_ASSERT(seq.index() <= capacity() && "full table!");
}
}
// Returns true if the table needs to be sampled.
// This should be called on insertion into an empty SOO table and in copy
// construction when the size can fit in SOO capacity.
bool should_sample_soo() const {
ABSL_SWISSTABLE_ASSERT(is_soo());
if (!ShouldSampleHashtablezInfoForAlloc<CharAlloc>()) return false;
return ABSL_PREDICT_FALSE(ShouldSampleNextTable());
}
void clear_backing_array(bool reuse) {
ABSL_SWISSTABLE_ASSERT(capacity() > DefaultCapacity());
ClearBackingArray(common(), GetPolicyFunctions(), &char_alloc_ref(), reuse,
SooEnabled());
}
void destroy_slots() {
ABSL_SWISSTABLE_ASSERT(!is_soo());
if (PolicyTraits::template destroy_is_trivial<Alloc>()) return;
auto destroy_slot = [&](const ctrl_t*, void* slot) {
this->destroy(static_cast<slot_type*>(slot));
};
if constexpr (SwisstableAssertAccessToDestroyedTable()) {
CommonFields common_copy(non_soo_tag_t{}, this->common());
common().set_capacity(InvalidCapacity::kDestroyed);
IterateOverFullSlots(common_copy, sizeof(slot_type), destroy_slot);
common().set_capacity(common_copy.capacity());
} else {
IterateOverFullSlots(common(), sizeof(slot_type), destroy_slot);
}
}
void dealloc() {
ABSL_SWISSTABLE_ASSERT(capacity() > DefaultCapacity());
// Unpoison before returning the memory to the allocator.
SanitizerUnpoisonMemoryRegion(slot_array(), sizeof(slot_type) * capacity());
infoz().Unregister();
DeallocateBackingArray<BackingArrayAlignment(alignof(slot_type)),
CharAlloc>(&char_alloc_ref(), capacity(), control(),
sizeof(slot_type), alignof(slot_type),
common().has_infoz());
}
void destructor_impl() {
if (SwisstableGenerationsEnabled() &&
capacity() >= InvalidCapacity::kMovedFrom) {
return;
}
if (capacity() == 0) return;
if (is_soo()) {
if (!empty()) {
ABSL_SWISSTABLE_IGNORE_UNINITIALIZED(destroy(soo_slot()));
}
return;
}
destroy_slots();
dealloc();
}
// Erases, but does not destroy, the value pointed to by `it`.
//
// This merely updates the pertinent control byte. This can be used in
// conjunction with Policy::transfer to move the object to another place.
void erase_meta_only(const_iterator it) {
ABSL_SWISSTABLE_ASSERT(!is_soo());
EraseMetaOnly(common(), static_cast<size_t>(it.control() - control()),
sizeof(slot_type));
}
size_t hash_of(slot_type* slot) const {
return PolicyTraits::apply(HashElement{hash_ref()},
PolicyTraits::element(slot));
}
void resize_full_soo_table_to_next_capacity() {
ABSL_SWISSTABLE_ASSERT(SooEnabled());
ABSL_SWISSTABLE_ASSERT(capacity() == SooCapacity());
ABSL_SWISSTABLE_ASSERT(!empty());
if constexpr (SooEnabled()) {
GrowFullSooTableToNextCapacity<PolicyTraits::transfer_uses_memcpy()
? OptimalMemcpySizeForSooSlotTransfer(
sizeof(slot_type))
: 0,
PolicyTraits::transfer_uses_memcpy()>(
common(), GetPolicyFunctions(), hash_of(soo_slot()));
}
}
// Casting directly from e.g. char* to slot_type* can cause compilation errors
// on objective-C. This function converts to void* first, avoiding the issue.
static slot_type* to_slot(void* buf) { return static_cast<slot_type*>(buf); }
// Requires that lhs does not have a full SOO slot.
static void move_common(bool rhs_is_full_soo, CharAlloc& rhs_alloc,
CommonFields& lhs, CommonFields&& rhs) {
if (PolicyTraits::transfer_uses_memcpy() || !rhs_is_full_soo) {
lhs = std::move(rhs);
} else {
lhs.move_non_heap_or_soo_fields(rhs);
rhs.RunWithReentrancyGuard([&] {
lhs.RunWithReentrancyGuard([&] {
PolicyTraits::transfer(&rhs_alloc, to_slot(lhs.soo_data()),
to_slot(rhs.soo_data()));
});
});
}
}
// Swaps common fields making sure to avoid memcpy'ing a full SOO slot if we
// aren't allowed to do so.
void swap_common(raw_hash_set& that) {
using std::swap;
if (PolicyTraits::transfer_uses_memcpy()) {
swap(common(), that.common());
return;
}
CommonFields tmp = CommonFields(uninitialized_tag_t{});
const bool that_is_full_soo = that.is_full_soo();
move_common(that_is_full_soo, that.char_alloc_ref(), tmp,
std::move(that.common()));
move_common(is_full_soo(), char_alloc_ref(), that.common(),
std::move(common()));
move_common(that_is_full_soo, that.char_alloc_ref(), common(),
std::move(tmp));
}
void annotate_for_bug_detection_on_move(
ABSL_ATTRIBUTE_UNUSED raw_hash_set& that) {
// We only enable moved-from validation when generations are enabled (rather
// than using NDEBUG) to avoid issues in which NDEBUG is enabled in some
// translation units but not in others.
if (SwisstableGenerationsEnabled()) {
that.common().set_capacity(this == &that ? InvalidCapacity::kSelfMovedFrom
: InvalidCapacity::kMovedFrom);
}
if (!SwisstableGenerationsEnabled() || capacity() == DefaultCapacity() ||
capacity() > kAboveMaxValidCapacity) {
return;
}
common().increment_generation();
if (!empty() && common().should_rehash_for_bug_detection_on_move()) {
ResizeAllocatedTableWithSeedChange(common(), GetPolicyFunctions(),
capacity());
}
}
template <bool propagate_alloc>
raw_hash_set& assign_impl(raw_hash_set&& that) {
// We don't bother checking for this/that aliasing. We just need to avoid
// breaking the invariants in that case.
destructor_impl();
move_common(that.is_full_soo(), that.char_alloc_ref(), common(),
std::move(that.common()));
hash_ref() = that.hash_ref();
eq_ref() = that.eq_ref();
CopyAlloc(char_alloc_ref(), that.char_alloc_ref(),
std::integral_constant<bool, propagate_alloc>());
that.common() = CommonFields::CreateDefault<SooEnabled()>();
annotate_for_bug_detection_on_move(that);
return *this;
}
raw_hash_set& move_elements_allocs_unequal(raw_hash_set&& that) {
const size_t size = that.size();
if (size == 0) return *this;
reserve(size);
for (iterator it = that.begin(); it != that.end(); ++it) {
insert(std::move(PolicyTraits::element(it.slot())));
that.destroy(it.slot());
}
if (!that.is_soo()) that.dealloc();
that.common() = CommonFields::CreateDefault<SooEnabled()>();
annotate_for_bug_detection_on_move(that);
return *this;
}
raw_hash_set& move_assign(raw_hash_set&& that,
std::true_type /*propagate_alloc*/) {
return assign_impl<true>(std::move(that));
}
raw_hash_set& move_assign(raw_hash_set&& that,
std::false_type /*propagate_alloc*/) {
if (char_alloc_ref() == that.char_alloc_ref()) {
return assign_impl<false>(std::move(that));
}
// Aliasing can't happen here because allocs would compare equal above.
assert(this != &that);
destructor_impl();
// We can't take over that's memory so we need to move each element.
// While moving elements, this should have that's hash/eq so copy hash/eq
// before moving elements.
hash_ref() = that.hash_ref();
eq_ref() = that.eq_ref();
return move_elements_allocs_unequal(std::move(that));
}
template <class K>
std::pair<iterator, bool> find_or_prepare_insert_soo(const K& key) {
if (empty()) {
if (should_sample_soo()) {
GrowEmptySooTableToNextCapacityForceSampling(common(),
GetPolicyFunctions());
} else {
common().set_full_soo();
return {soo_iterator(), true};
}
} else if (PolicyTraits::apply(EqualElement<K>{key, eq_ref()},
PolicyTraits::element(soo_slot()))) {
return {soo_iterator(), false};
} else {
resize_full_soo_table_to_next_capacity();
}
const size_t index =
PrepareInsertAfterSoo(hash_ref()(key), sizeof(slot_type), common());
return {iterator_at(index), true};
}
template <class K>
std::pair<iterator, bool> find_or_prepare_insert_non_soo(const K& key) {
ABSL_SWISSTABLE_ASSERT(!is_soo());
prefetch_heap_block();
auto hash = hash_ref()(key);
auto seq = probe(common(), hash);
const ctrl_t* ctrl = control();
while (true) {
Group g{ctrl + seq.offset()};
for (uint32_t i : g.Match(H2(hash))) {
if (ABSL_PREDICT_TRUE(PolicyTraits::apply(
EqualElement<K>{key, eq_ref()},
PolicyTraits::element(slot_array() + seq.offset(i)))))
return {iterator_at(seq.offset(i)), false};
}
auto mask_empty = g.MaskEmpty();
if (ABSL_PREDICT_TRUE(mask_empty)) {
size_t target = seq.offset(
GetInsertionOffset(mask_empty, capacity(), hash, common().seed()));
return {iterator_at(PrepareInsertNonSoo(common(), GetPolicyFunctions(),
hash,
FindInfo{target, seq.index()})),
true};
}
seq.next();
ABSL_SWISSTABLE_ASSERT(seq.index() <= capacity() && "full table!");
}
}
protected:
// Asserts for correctness that we run on find/find_or_prepare_insert.
template <class K>
void AssertOnFind(ABSL_ATTRIBUTE_UNUSED const K& key) {
AssertHashEqConsistent(key);
AssertNotDebugCapacity();
}
// Asserts that the capacity is not a sentinel invalid value.
void AssertNotDebugCapacity() const {
#ifdef NDEBUG
if (!SwisstableGenerationsEnabled()) {
return;
}
#endif
if (ABSL_PREDICT_TRUE(capacity() <
InvalidCapacity::kAboveMaxValidCapacity)) {
return;
}
assert(capacity() != InvalidCapacity::kReentrance &&
"Reentrant container access during element construction/destruction "
"is not allowed.");
if constexpr (SwisstableAssertAccessToDestroyedTable()) {
if (capacity() == InvalidCapacity::kDestroyed) {
ABSL_RAW_LOG(FATAL, "Use of destroyed hash table.");
}
}
if (SwisstableGenerationsEnabled() &&
ABSL_PREDICT_FALSE(capacity() >= InvalidCapacity::kMovedFrom)) {
if (capacity() == InvalidCapacity::kSelfMovedFrom) {
// If this log triggers, then a hash table was move-assigned to itself
// and then used again later without being reinitialized.
ABSL_RAW_LOG(FATAL, "Use of self-move-assigned hash table.");
}
ABSL_RAW_LOG(FATAL, "Use of moved-from hash table.");
}
}
// Asserts that hash and equal functors provided by the user are consistent,
// meaning that `eq(k1, k2)` implies `hash(k1)==hash(k2)`.
template <class K>
void AssertHashEqConsistent(const K& key) {
#ifdef NDEBUG
return;
#endif
// If the hash/eq functors are known to be consistent, then skip validation.
if (std::is_same<hasher, absl::container_internal::StringHash>::value &&
std::is_same<key_equal, absl::container_internal::StringEq>::value) {
return;
}
if (std::is_scalar<key_type>::value &&
std::is_same<hasher, absl::Hash<key_type>>::value &&
std::is_same<key_equal, std::equal_to<key_type>>::value) {
return;
}
if (empty()) return;
const size_t hash_of_arg = hash_ref()(key);
const auto assert_consistent = [&](const ctrl_t*, void* slot) {
const value_type& element =
PolicyTraits::element(static_cast<slot_type*>(slot));
const bool is_key_equal =
PolicyTraits::apply(EqualElement<K>{key, eq_ref()}, element);
if (!is_key_equal) return;
const size_t hash_of_slot =
PolicyTraits::apply(HashElement{hash_ref()}, element);
ABSL_ATTRIBUTE_UNUSED const bool is_hash_equal =
hash_of_arg == hash_of_slot;
assert((!is_key_equal || is_hash_equal) &&
"eq(k1, k2) must imply that hash(k1) == hash(k2). "
"hash/eq functors are inconsistent.");
};
if (is_soo()) {
assert_consistent(/*unused*/ nullptr, soo_slot());
return;
}
// We only do validation for small tables so that it's constant time.
if (capacity() > 16) return;
IterateOverFullSlots(common(), sizeof(slot_type), assert_consistent);
}
// Attempts to find `key` in the table; if it isn't found, returns an iterator
// where the value can be inserted into, with the control byte already set to
// `key`'s H2. Returns a bool indicating whether an insertion can take place.
template <class K>
std::pair<iterator, bool> find_or_prepare_insert(const K& key) {
AssertOnFind(key);
if (is_soo()) return find_or_prepare_insert_soo(key);
return find_or_prepare_insert_non_soo(key);
}
// Constructs the value in the space pointed by the iterator. This only works
// after an unsuccessful find_or_prepare_insert() and before any other
// modifications happen in the raw_hash_set.
//
// PRECONDITION: iter was returned from find_or_prepare_insert(k), where k is
// the key decomposed from `forward<Args>(args)...`, and the bool returned by
// find_or_prepare_insert(k) was true.
// POSTCONDITION: *m.iterator_at(i) == value_type(forward<Args>(args)...).
template <class... Args>
void emplace_at(iterator iter, Args&&... args) {
construct(iter.slot(), std::forward<Args>(args)...);
assert(PolicyTraits::apply(FindElement{*this}, *iter) == iter &&
"constructed value does not match the lookup key");
}
iterator iterator_at(size_t i) ABSL_ATTRIBUTE_LIFETIME_BOUND {
return {control() + i, slot_array() + i, common().generation_ptr()};
}
const_iterator iterator_at(size_t i) const ABSL_ATTRIBUTE_LIFETIME_BOUND {
return const_cast<raw_hash_set*>(this)->iterator_at(i);
}
reference unchecked_deref(iterator it) { return it.unchecked_deref(); }
private:
friend struct RawHashSetTestOnlyAccess;
// The number of slots we can still fill without needing to rehash.
//
// This is stored separately due to tombstones: we do not include tombstones
// in the growth capacity, because we'd like to rehash when the table is
// otherwise filled with tombstones: otherwise, probe sequences might get
// unacceptably long without triggering a rehash. Callers can also force a
// rehash via the standard `rehash(0)`, which will recompute this value as a
// side-effect.
//
// See `CapacityToGrowth()`.
size_t growth_left() const {
ABSL_SWISSTABLE_ASSERT(!is_soo());
return common().growth_left();
}
GrowthInfo& growth_info() {
ABSL_SWISSTABLE_ASSERT(!is_soo());
return common().growth_info();
}
GrowthInfo growth_info() const {
ABSL_SWISSTABLE_ASSERT(!is_soo());
return common().growth_info();
}
// Prefetch the heap-allocated memory region to resolve potential TLB and
// cache misses. This is intended to overlap with execution of calculating the
// hash for a key.
void prefetch_heap_block() const {
ABSL_SWISSTABLE_ASSERT(!is_soo());
#if ABSL_HAVE_BUILTIN(__builtin_prefetch) || defined(__GNUC__)
__builtin_prefetch(control(), 0, 1);
#endif
}
CommonFields& common() { return settings_.template get<0>(); }
const CommonFields& common() const { return settings_.template get<0>(); }
ctrl_t* control() const {
ABSL_SWISSTABLE_ASSERT(!is_soo());
return common().control();
}
slot_type* slot_array() const {
ABSL_SWISSTABLE_ASSERT(!is_soo());
return static_cast<slot_type*>(common().slot_array());
}
slot_type* soo_slot() {
ABSL_SWISSTABLE_ASSERT(is_soo());
ABSL_SWISSTABLE_IGNORE_UNINITIALIZED_RETURN(
static_cast<slot_type*>(common().soo_data()));
}
const slot_type* soo_slot() const {
ABSL_SWISSTABLE_IGNORE_UNINITIALIZED_RETURN(
const_cast<raw_hash_set*>(this)->soo_slot());
}
iterator soo_iterator() {
return {SooControl(), soo_slot(), common().generation_ptr()};
}
const_iterator soo_iterator() const {
return const_cast<raw_hash_set*>(this)->soo_iterator();
}
HashtablezInfoHandle infoz() {
ABSL_SWISSTABLE_ASSERT(!is_soo());
return common().infoz();
}
hasher& hash_ref() { return settings_.template get<1>(); }
const hasher& hash_ref() const { return settings_.template get<1>(); }
key_equal& eq_ref() { return settings_.template get<2>(); }
const key_equal& eq_ref() const { return settings_.template get<2>(); }
CharAlloc& char_alloc_ref() { return settings_.template get<3>(); }
const CharAlloc& char_alloc_ref() const {
return settings_.template get<3>();
}
static void* get_char_alloc_ref_fn(CommonFields& common) {
auto* h = reinterpret_cast<raw_hash_set*>(&common);
return &h->char_alloc_ref();
}
static void* get_hash_ref_fn(CommonFields& common) {
auto* h = reinterpret_cast<raw_hash_set*>(&common);
// TODO(b/397453582): Remove support for const hasher.
return const_cast<std::remove_const_t<hasher>*>(&h->hash_ref());
}
static void transfer_slots_fn(void* set, void* dst, void* src, size_t count) {
auto* src_slot = to_slot(src);
auto* dst_slot = to_slot(dst);
auto* h = static_cast<raw_hash_set*>(set);
for (; count > 0; --count, ++src_slot, ++dst_slot) {
h->transfer(dst_slot, src_slot);
}
}
// TODO(b/382423690): Type erase by GetKey + Hash for memcpyable types.
static size_t find_new_positions_and_transfer_slots_fn(CommonFields& common,
ctrl_t* old_ctrl,
void* old_slots,
size_t old_capacity) {
auto* set = reinterpret_cast<raw_hash_set*>(&common);
slot_type* new_slots = set->slot_array();
slot_type* old_slots_ptr = to_slot(old_slots);
const auto insert_slot = [&](slot_type* slot) {
size_t hash = PolicyTraits::apply(HashElement{set->hash_ref()},
PolicyTraits::element(slot));
auto target = find_first_non_full(common, hash);
SetCtrl(common, target.offset, H2(hash), sizeof(slot_type));
set->transfer(new_slots + target.offset, slot);
return target.probe_length;
};
size_t total_probe_length = 0;
for (size_t i = 0; i < old_capacity; ++i) {
if (IsFull(old_ctrl[i])) {
total_probe_length += insert_slot(old_slots_ptr + i);
}
}
return total_probe_length;
}
static const PolicyFunctions& GetPolicyFunctions() {
static_assert(sizeof(slot_type) <= (std::numeric_limits<uint32_t>::max)(),
"Slot size is too large. Use std::unique_ptr for value type "
"or use absl::node_hash_{map,set}.");
static_assert(alignof(slot_type) <=
size_t{(std::numeric_limits<uint16_t>::max)()});
static_assert(sizeof(key_type) <=
size_t{(std::numeric_limits<uint32_t>::max)()});
static_assert(sizeof(value_type) <=
size_t{(std::numeric_limits<uint32_t>::max)()});
static constexpr size_t kBackingArrayAlignment =
BackingArrayAlignment(alignof(slot_type));
static constexpr PolicyFunctions value = {
static_cast<uint32_t>(sizeof(key_type)),
static_cast<uint32_t>(sizeof(value_type)),
static_cast<uint16_t>(sizeof(slot_type)),
static_cast<uint16_t>(alignof(slot_type)),
static_cast<uint8_t>(SooEnabled() ? SooCapacity() : 0),
ShouldSampleHashtablezInfoForAlloc<CharAlloc>(),
// TODO(b/328722020): try to type erase
// for standard layout and alignof(Hash) <= alignof(CommonFields).
std::is_empty_v<hasher> ? &GetRefForEmptyClass
: &raw_hash_set::get_hash_ref_fn,
PolicyTraits::template get_hash_slot_fn<hasher>(),
PolicyTraits::transfer_uses_memcpy()
? TransferRelocatable<sizeof(slot_type)>
: &raw_hash_set::transfer_slots_fn,
std::is_empty_v<Alloc> ? &GetRefForEmptyClass
: &raw_hash_set::get_char_alloc_ref_fn,
&AllocateBackingArray<kBackingArrayAlignment, CharAlloc>,
&DeallocateBackingArray<kBackingArrayAlignment, CharAlloc>,
&raw_hash_set::find_new_positions_and_transfer_slots_fn};
return value;
}
// Bundle together CommonFields plus other objects which might be empty.
// CompressedTuple will ensure that sizeof is not affected by any of the empty
// fields that occur after CommonFields.
absl::container_internal::CompressedTuple<CommonFields, hasher, key_equal,
CharAlloc>
settings_{CommonFields::CreateDefault<SooEnabled()>(), hasher{},
key_equal{}, CharAlloc{}};
};
// Friend access for free functions in raw_hash_set.h.
struct HashtableFreeFunctionsAccess {
template <class Predicate, typename Set>
static typename Set::size_type EraseIf(Predicate& pred, Set* c) {
if (c->empty()) {
return 0;
}
if (c->is_soo()) {
auto it = c->soo_iterator();
if (!pred(*it)) {
ABSL_SWISSTABLE_ASSERT(c->size() == 1 &&
"hash table was modified unexpectedly");
return 0;
}
c->destroy(it.slot());
c->common().set_empty_soo();
return 1;
}
ABSL_ATTRIBUTE_UNUSED const size_t original_size_for_assert = c->size();
size_t num_deleted = 0;
using SlotType = typename Set::slot_type;
IterateOverFullSlots(
c->common(), sizeof(SlotType),
[&](const ctrl_t* ctrl, void* slot_void) {
auto* slot = static_cast<SlotType*>(slot_void);
if (pred(Set::PolicyTraits::element(slot))) {
c->destroy(slot);
EraseMetaOnly(c->common(), static_cast<size_t>(ctrl - c->control()),
sizeof(*slot));
++num_deleted;
}
});
// NOTE: IterateOverFullSlots allow removal of the current element, so we
// verify the size additionally here.
ABSL_SWISSTABLE_ASSERT(original_size_for_assert - num_deleted ==
c->size() &&
"hash table was modified unexpectedly");
return num_deleted;
}
template <class Callback, typename Set>
static void ForEach(Callback& cb, Set* c) {
if (c->empty()) {
return;
}
if (c->is_soo()) {
cb(*c->soo_iterator());
return;
}
using SlotType = typename Set::slot_type;
using ElementTypeWithConstness = decltype(*c->begin());
IterateOverFullSlots(
c->common(), sizeof(SlotType), [&cb](const ctrl_t*, void* slot) {
ElementTypeWithConstness& element =
Set::PolicyTraits::element(static_cast<SlotType*>(slot));
cb(element);
});
}
};
// Erases all elements that satisfy the predicate `pred` from the container `c`.
template <typename P, typename H, typename E, typename A, typename Predicate>
typename raw_hash_set<P, H, E, A>::size_type EraseIf(
Predicate& pred, raw_hash_set<P, H, E, A>* c) {
return HashtableFreeFunctionsAccess::EraseIf(pred, c);
}
// Calls `cb` for all elements in the container `c`.
template <typename P, typename H, typename E, typename A, typename Callback>
void ForEach(Callback& cb, raw_hash_set<P, H, E, A>* c) {
return HashtableFreeFunctionsAccess::ForEach(cb, c);
}
template <typename P, typename H, typename E, typename A, typename Callback>
void ForEach(Callback& cb, const raw_hash_set<P, H, E, A>* c) {
return HashtableFreeFunctionsAccess::ForEach(cb, c);
}
namespace hashtable_debug_internal {
template <typename Set>
struct HashtableDebugAccess<Set, absl::void_t<typename Set::raw_hash_set>> {
using Traits = typename Set::PolicyTraits;
using Slot = typename Traits::slot_type;
static size_t GetNumProbes(const Set& set,
const typename Set::key_type& key) {
if (set.is_soo()) return 0;
size_t num_probes = 0;
size_t hash = set.hash_ref()(key);
auto seq = probe(set.common(), hash);
const ctrl_t* ctrl = set.control();
while (true) {
container_internal::Group g{ctrl + seq.offset()};
for (uint32_t i : g.Match(container_internal::H2(hash))) {
if (Traits::apply(
typename Set::template EqualElement<typename Set::key_type>{
key, set.eq_ref()},
Traits::element(set.slot_array() + seq.offset(i))))
return num_probes;
++num_probes;
}
if (g.MaskEmpty()) return num_probes;
seq.next();
++num_probes;
}
}
static size_t AllocatedByteSize(const Set& c) {
size_t capacity = c.capacity();
if (capacity == 0) return 0;
size_t m =
c.is_soo() ? 0 : c.common().alloc_size(sizeof(Slot), alignof(Slot));
size_t per_slot = Traits::space_used(static_cast<const Slot*>(nullptr));
if (per_slot != ~size_t{}) {
m += per_slot * c.size();
} else {
for (auto it = c.begin(); it != c.end(); ++it) {
m += Traits::space_used(it.slot());
}
}
return m;
}
};
} // namespace hashtable_debug_internal
// Extern template instantiations reduce binary size and linker input size.
// Function definition is in raw_hash_set.cc.
extern template void GrowFullSooTableToNextCapacity<0, false>(
CommonFields&, const PolicyFunctions&, size_t);
extern template void GrowFullSooTableToNextCapacity<1, true>(
CommonFields&, const PolicyFunctions&, size_t);
extern template void GrowFullSooTableToNextCapacity<4, true>(
CommonFields&, const PolicyFunctions&, size_t);
extern template void GrowFullSooTableToNextCapacity<8, true>(
CommonFields&, const PolicyFunctions&, size_t);
#if UINTPTR_MAX == UINT64_MAX
extern template void GrowFullSooTableToNextCapacity<16, true>(
CommonFields&, const PolicyFunctions&, size_t);
#endif
} // namespace container_internal
ABSL_NAMESPACE_END
} // namespace absl
#undef ABSL_SWISSTABLE_ENABLE_GENERATIONS
#undef ABSL_SWISSTABLE_IGNORE_UNINITIALIZED
#undef ABSL_SWISSTABLE_IGNORE_UNINITIALIZED_RETURN
#undef ABSL_SWISSTABLE_ASSERT
#endif // ABSL_CONTAINER_INTERNAL_RAW_HASH_SET_H_