1 // Copyright 2024 The Pigweed Authors 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); you may not 4 // use this file except in compliance with the License. You may obtain a copy of 5 // the License at 6 // 7 // https://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, WITHOUT 11 // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the 12 // License for the specific language governing permissions and limitations under 13 // the License. 14 #pragma once 15 16 #include <atomic> 17 #include <cstring> 18 #include <optional> 19 20 #include "pw_assert/assert.h" 21 #include "pw_bytes/span.h" 22 #include "pw_multibuf/chunk.h" 23 24 namespace pw::multibuf { 25 26 /// A `ChunkRegionTracker` that uses inline memory to create a single `Chunk` 27 /// with the only caveat that the provided `Chunk` cannot be split. All attempts 28 /// will result in `std::nullopt`. 29 class SingleChunkRegionTracker : public ChunkRegionTracker { 30 public: 31 /// Constructs a region tracker with a single `Chunk` that maps to `region`, 32 /// which must outlive this tracker and any `OwnedChunk` it creates. SingleChunkRegionTracker(ByteSpan region)33 explicit SingleChunkRegionTracker(ByteSpan region) : region_(region) {} ~SingleChunkRegionTracker()34 ~SingleChunkRegionTracker() override { Destroy(); } 35 36 /// Gets a `Chunk` of a given size, which must be less than or equal to the 37 /// provided region. 38 /// 39 /// Returns: 40 /// An `OwnedChunk` if the `Chunk` is free, otherwise `std::nullopt`, in 41 /// which case `GetChunk()` can be called again. GetChunk(size_t size)42 std::optional<OwnedChunk> GetChunk(size_t size) { 43 PW_DASSERT(size <= region_.size()); 44 // Since this is a single `Chunk` region, re-create the first `Chunk` is 45 // allowed if freed. 46 std::optional<OwnedChunk> chunk = CreateFirstChunk(); 47 if (chunk.has_value() && size < region_.size()) { 48 (*chunk)->Truncate(size); 49 } 50 return chunk; 51 } 52 Destroy()53 void Destroy() final { 54 // Nothing to release here. 55 PW_ASSERT(!chunk_in_use_); 56 } 57 Region()58 ByteSpan Region() const final { return region_; } 59 AllocateChunkClass()60 void* AllocateChunkClass() final { 61 bool in_use = false; 62 if (!chunk_in_use_.compare_exchange_strong(in_use, true)) { 63 return nullptr; 64 } 65 return &chunk_storage_; 66 } 67 DeallocateChunkClass(void * chunk)68 void DeallocateChunkClass(void* chunk) final { 69 PW_ASSERT(chunk == chunk_storage_.data()); 70 // Mark the `Chunk` as not in use and zero-out the region and chunk storage. 71 std::memset(chunk_storage_.data(), 0, chunk_storage_.size()); 72 std::memset(region_.data(), 0, region_.size()); 73 chunk_in_use_ = false; 74 } 75 76 private: 77 ByteSpan region_; 78 std::atomic<bool> chunk_in_use_ = false; 79 alignas(Chunk) std::array<std::byte, sizeof(Chunk)> chunk_storage_; 80 }; 81 82 } // namespace pw::multibuf 83