| // Copyright 2020 The Pigweed 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. |
| #pragma once |
| |
| #include <array> |
| |
| #include "pw_containers/vector.h" |
| #include "pw_span/span.h" |
| #include "pw_status/status.h" |
| |
| namespace pw::allocator { |
| |
| template <size_t kNumBuckets> |
| class FreeListBuffer; |
| |
| // Basic freelist implementation for an allocator. |
| // This implementation buckets by chunk size, with a list of user-provided |
| // buckets. Each bucket is a linked list of storage chunks. Because this |
| // freelist uses the added chunks themselves as list nodes, there is lower bound |
| // of sizeof(FreeList.FreeListNode) bytes for chunks which can be added to this |
| // freelist. There is also an implicit bucket for "everything else", for chunks |
| // which do not fit into a bucket. |
| // |
| // Each added chunk will be added to the smallest bucket under which it fits. If |
| // it does not fit into any user-provided bucket, it will be added to the |
| // default bucket. |
| // |
| // As an example, assume that the FreeList is configured with buckets of sizes |
| // {64, 128, 256 and 512} bytes. The internal state may look like the following. |
| // |
| // bucket[0] (64B) --> chunk[12B] --> chunk[42B] --> chunk[64B] --> NULL |
| // bucket[1] (128B) --> chunk[65B] --> chunk[72B] --> NULL |
| // bucket[2] (256B) --> NULL |
| // bucket[3] (512B) --> chunk[312B] --> chunk[512B] --> chunk[416B] --> NULL |
| // bucket[4] (implicit) --> chunk[1024B] --> chunk[513B] --> NULL |
| // |
| // Note that added chunks should be aligned to a 4-byte boundary. |
| // |
| // This class is split into two parts; FreeList implements all of the |
| // logic, and takes in pointers for two pw::Vector instances for its storage. |
| // This prevents us from having to specialise this class for every kMaxSize |
| // parameter for the vector. FreeListBuffer then provides the storage for these |
| // two pw::Vector instances and instantiates FreeListInternal. |
| class FreeList { |
| public: |
| // Remove copy/move ctors |
| FreeList(const FreeList& other) = delete; |
| FreeList(FreeList&& other) = delete; |
| FreeList& operator=(const FreeList& other) = delete; |
| FreeList& operator=(FreeList&& other) = delete; |
| |
| // Adds a chunk to this freelist. Returns: |
| // OK: The chunk was added successfully |
| // OUT_OF_RANGE: The chunk could not be added for size reasons (e.g. if |
| // the chunk is too small to store the FreeListNode). |
| Status AddChunk(span<std::byte> chunk); |
| |
| // Finds an eligible chunk for an allocation of size `size`. Note that this |
| // will return the first allocation possible within a given bucket, it does |
| // not currently optimize for finding the smallest chunk. Returns a span |
| // representing the chunk. This will be "valid" on success, and will have size |
| // = 0 on failure (if there were no chunks available for that allocation). |
| span<std::byte> FindChunk(size_t size) const; |
| |
| // Remove a chunk from this freelist. Returns: |
| // OK: The chunk was removed successfully |
| // NOT_FOUND: The chunk could not be found in this freelist. |
| Status RemoveChunk(span<std::byte> chunk); |
| |
| private: |
| // For a given size, find which index into chunks_ the node should be written |
| // to. |
| unsigned short FindChunkPtrForSize(size_t size, bool non_null) const; |
| |
| private: |
| template <size_t kNumBuckets> |
| friend class FreeListBuffer; |
| |
| struct FreeListNode { |
| // TODO: Double-link this? It'll make removal easier/quicker. |
| FreeListNode* next; |
| size_t size; |
| }; |
| |
| constexpr FreeList(Vector<FreeListNode*>& chunks, Vector<size_t>& sizes) |
| : chunks_(chunks), sizes_(sizes) {} |
| |
| Vector<FreeListNode*>& chunks_; |
| Vector<size_t>& sizes_; |
| }; |
| |
| // Holder for FreeList's storage. |
| template <size_t kNumBuckets> |
| class FreeListBuffer : public FreeList { |
| public: |
| // These constructors are a little hacky because of the initialization order. |
| // Because FreeList has a trivial constructor, this is safe, however. |
| explicit FreeListBuffer(std::initializer_list<size_t> sizes) |
| : FreeList(chunks_, sizes_), sizes_(sizes), chunks_(kNumBuckets + 1, 0) {} |
| explicit FreeListBuffer(std::array<size_t, kNumBuckets> sizes) |
| : FreeList(chunks_, sizes_), |
| sizes_(sizes.begin(), sizes.end()), |
| chunks_(kNumBuckets + 1, 0) {} |
| |
| private: |
| Vector<size_t, kNumBuckets> sizes_; |
| Vector<FreeList::FreeListNode*, kNumBuckets + 1> chunks_; |
| }; |
| |
| } // namespace pw::allocator |