| // Protocol Buffers - Google's data interchange format |
| // Copyright 2008 Google Inc. All rights reserved. |
| // https://developers.google.com/protocol-buffers/ |
| // |
| // Redistribution and use in source and binary forms, with or without |
| // modification, are permitted provided that the following conditions are |
| // met: |
| // |
| // * Redistributions of source code must retain the above copyright |
| // notice, this list of conditions and the following disclaimer. |
| // * Redistributions in binary form must reproduce the above |
| // copyright notice, this list of conditions and the following disclaimer |
| // in the documentation and/or other materials provided with the |
| // distribution. |
| // * Neither the name of Google Inc. nor the names of its |
| // contributors may be used to endorse or promote products derived from |
| // this software without specific prior written permission. |
| // |
| // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
| // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
| // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
| // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
| // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
| // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
| // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
| // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| |
| #ifndef GOOGLE_PROTOBUF_ARENA_CLEANUP_H__ |
| #define GOOGLE_PROTOBUF_ARENA_CLEANUP_H__ |
| |
| #include <cstddef> |
| #include <cstdint> |
| #include <string> |
| |
| #include "google/protobuf/stubs/logging.h" |
| #include "google/protobuf/stubs/common.h" |
| #include "absl/base/attributes.h" |
| |
| |
| |
| namespace google { |
| namespace protobuf { |
| namespace internal { |
| namespace cleanup { |
| |
| // Helper function invoking the destructor of `object` |
| template <typename T> |
| void arena_destruct_object(void* object) { |
| reinterpret_cast<T*>(object)->~T(); |
| } |
| |
| // Tag defines the type of cleanup / cleanup object. This tag is stored in the |
| // lowest 2 bits of the `elem` value identifying the type of node. All node |
| // types must start with a `uintptr_t` that stores `Tag` in its low two bits. |
| enum class Tag : uintptr_t { |
| kDynamic = 0, // DynamicNode |
| kString = 1, // StringNode (std::string) |
| }; |
| |
| // DynamicNode contains the object (`elem`) that needs to be |
| // destroyed, and the function to destroy it (`destructor`) |
| // elem must be aligned at minimum on a 4 byte boundary. |
| struct DynamicNode { |
| uintptr_t elem; |
| void (*destructor)(void*); |
| }; |
| |
| // StringNode contains a `std::string` object (`elem`) that needs to be |
| // destroyed. The lowest 2 bits of `elem` contain the non-zero kString tag. |
| struct StringNode { |
| uintptr_t elem; |
| }; |
| |
| |
| // EnableSpecializedTags() return true if the alignment of tagged objects |
| // such as std::string allow us to poke tags in the 2 LSB bits. |
| inline constexpr bool EnableSpecializedTags() { |
| // For now we require 2 bits |
| return alignof(std::string) >= 8; |
| } |
| |
| // Adds a cleanup entry identified by `tag` at memory location `pos`. |
| inline ABSL_ATTRIBUTE_ALWAYS_INLINE void CreateNode(Tag tag, void* pos, |
| const void* elem_raw, |
| void (*destructor)(void*)) { |
| auto elem = reinterpret_cast<uintptr_t>(elem_raw); |
| if (EnableSpecializedTags()) { |
| GOOGLE_DCHECK_EQ(elem & 3, 0ULL); // Must be aligned |
| switch (tag) { |
| case Tag::kString: { |
| StringNode n = {elem | static_cast<uintptr_t>(Tag::kString)}; |
| memcpy(pos, &n, sizeof(n)); |
| return; |
| } |
| default: |
| break; |
| } |
| } |
| DynamicNode n = {elem, destructor}; |
| memcpy(pos, &n, sizeof(n)); |
| } |
| |
| // Optimization: performs a prefetch on `elem_address`. |
| inline ABSL_ATTRIBUTE_ALWAYS_INLINE void PrefetchNode( |
| const void* elem_address) { |
| (void)elem_address; |
| } |
| |
| // Destroys the node idenitfied by `tag` stored at memory location `pos`. |
| inline ABSL_ATTRIBUTE_ALWAYS_INLINE void DestroyNode(Tag tag, const void* pos) { |
| if (EnableSpecializedTags()) { |
| switch (tag) { |
| case Tag::kString: { |
| StringNode n; |
| memcpy(&n, pos, sizeof(n)); |
| auto* s = reinterpret_cast<std::string*>(n.elem & ~0x7ULL); |
| // Some compilers don't like fully qualified explicit dtor calls, |
| // so use an alias to avoid having to type `::`. |
| using string_type = std::string; |
| s->~string_type(); |
| return; |
| } |
| default: |
| break; |
| } |
| } |
| DynamicNode n; |
| memcpy(&n, pos, sizeof(n)); |
| n.destructor(reinterpret_cast<void*>(n.elem)); |
| } |
| |
| // Returns the `tag` identifying the type of object for `destructor` or |
| // kDynamic if `destructor` does not identify a well know object type. |
| inline ABSL_ATTRIBUTE_ALWAYS_INLINE Tag Type(void (*destructor)(void*)) { |
| if (EnableSpecializedTags()) { |
| if (destructor == &arena_destruct_object<std::string>) { |
| return Tag::kString; |
| } |
| } |
| return Tag::kDynamic; |
| } |
| |
| // Returns the `tag` identifying the type of object stored at memory location |
| // `elem`, which represents the first uintptr_t value in the node. |
| inline ABSL_ATTRIBUTE_ALWAYS_INLINE Tag Type(void* raw) { |
| if (!EnableSpecializedTags()) return Tag::kDynamic; |
| |
| uintptr_t elem; |
| memcpy(&elem, raw, sizeof(elem)); |
| switch (static_cast<Tag>(elem & 0x7ULL)) { |
| case Tag::kDynamic: |
| return Tag::kDynamic; |
| case Tag::kString: |
| return Tag::kString; |
| default: |
| GOOGLE_LOG(FATAL) << "Corrupted cleanup tag: " << (elem & 0x7ULL); |
| return Tag::kDynamic; |
| } |
| } |
| |
| // Returns the required size in bytes off the node type identified by `tag`. |
| inline ABSL_ATTRIBUTE_ALWAYS_INLINE size_t Size(Tag tag) { |
| if (!EnableSpecializedTags()) return sizeof(DynamicNode); |
| |
| switch (tag) { |
| case Tag::kDynamic: |
| return sizeof(DynamicNode); |
| case Tag::kString: |
| return sizeof(StringNode); |
| default: |
| GOOGLE_LOG(FATAL) << "Corrupted cleanup tag: " << static_cast<int>(tag); |
| return sizeof(DynamicNode); |
| } |
| } |
| |
| // Returns the required size in bytes off the node type for `destructor`. |
| inline ABSL_ATTRIBUTE_ALWAYS_INLINE size_t Size(void (*destructor)(void*)) { |
| return destructor == nullptr ? 0 : Size(Type(destructor)); |
| } |
| |
| } // namespace cleanup |
| } // namespace internal |
| } // namespace protobuf |
| } // namespace google |
| |
| #endif // GOOGLE_PROTOBUF_ARENA_CLEANUP_H__ |