best_fit.h

// Copyright 2024 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 <cstddef>
#include <limits>
 
#include "pw_allocator/block/detailed_block.h"
#include "pw_allocator/block_allocator.h"
#include "pw_allocator/bucket/fast_sorted.h"
#include "pw_allocator/bucket/sorted.h"
#include "pw_allocator/config.h"
 
namespace pw::allocator {
 
 
template <typename OffsetType>
using BestFitBlock = DetailedBlock<OffsetType, GenericFastSortedItem>;
 
template <typename BlockType = BestFitBlock<uintptr_t>>
class BestFitAllocator : public BlockAllocator<BlockType> {
 private:
  using SmallBucket = ForwardSortedBucket<BlockType>;
  using LargeBucket = FastSortedBucket<BlockType>;
 
 public:
  using Base = BlockAllocator<BlockType>;
 
  constexpr BestFitAllocator() = default;
 
  BestFitAllocator(ByteSpan region) { Base::Init(region); }
 
 private:
  size_t DoGetMaxAllocatable() override {
    const BlockType* largest = large_bucket_.empty()
                                   ? small_bucket_.FindLargest()
                                   : large_bucket_.FindLargest();
    return largest == nullptr ? 0 : largest->InnerSize();
  }
 
  BlockResult<BlockType> ChooseBlock(Layout layout) override {
    // The small bucket is slower; skip it if we can.
    BlockType* block = nullptr;
    if (layout.size() < sizeof(typename LargeBucket::ItemType)) {
      block = small_bucket_.RemoveCompatible(layout);
      if (block != nullptr) {
        return BlockType::AllocFirst(std::move(block), layout);
      }
    }
    block = large_bucket_.RemoveCompatible(layout);
    if (block != nullptr) {
      return BlockType::AllocFirst(std::move(block), layout);
    }
    return BlockResult<BlockType>(nullptr, Status::NotFound());
  }
 
  void ReserveBlock(BlockType& block) override {
    // The small bucket is slower; skip it if we can.
    if (!large_bucket_.Remove(block)) {
      std::ignore = small_bucket_.Remove(block);
    }
  }
 
  void RecycleBlock(BlockType& block) override {
    if (block.InnerSize() < sizeof(typename LargeBucket::ItemType)) {
      std::ignore = small_bucket_.Add(block);
    } else {
      std::ignore = large_bucket_.Add(block);
    }
  }
 
  SmallBucket small_bucket_;
  LargeBucket large_bucket_;
};
 
 
}  // namespace pw::allocator