first_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 <limits>
 
#include "pw_allocator/block/detailed_block.h"
#include "pw_allocator/block_allocator.h"
#include "pw_allocator/bucket/sequenced.h"
 
namespace pw::allocator {
 
 
template <typename OffsetType>
using FirstFitBlock = DetailedBlock<OffsetType, SequencedItem>;
 
template <typename BlockType = FirstFitBlock<uintptr_t>>
class FirstFitAllocator : public BlockAllocator<BlockType> {
 public:
  using Base = BlockAllocator<BlockType>;
 
  constexpr FirstFitAllocator() = default;
 
  FirstFitAllocator(ByteSpan region) { Base::Init(region); }
 
  FirstFitAllocator(ByteSpan region, size_t threshold);
 
  void set_threshold(size_t threshold) { bucket_.set_threshold(threshold); }
 
 private:
  size_t DoGetMaxAllocatable() override;
 
  BlockResult<BlockType> ChooseBlock(Layout layout) override;
 
  void ReserveBlock(BlockType& block) override {
    std::ignore = bucket_.Remove(block);
  }
 
  void RecycleBlock(BlockType& block) override {
    std::ignore = bucket_.Add(block);
  }
 
  SequencedBucket<BlockType> bucket_;
};
 
 
// Template method implementations.
 
template <typename BlockType>
FirstFitAllocator<BlockType>::FirstFitAllocator(ByteSpan region,
                                                size_t threshold) {
  Base::Init(region);
  bucket_.set_threshold(threshold);
}
 
template <typename BlockType>
size_t FirstFitAllocator<BlockType>::DoGetMaxAllocatable() {
  const BlockType* largest = bucket_.FindLargest();
  return largest == nullptr ? 0 : largest->InnerSize();
}
 
template <typename BlockType>
BlockResult<BlockType> FirstFitAllocator<BlockType>::ChooseBlock(
    Layout layout) {
  BlockType* block = bucket_.RemoveCompatible(layout);
  if (block == nullptr) {
    return BlockResult<BlockType>(nullptr, Status::NotFound());
  }
  if (layout.size() < bucket_.threshold()) {
    return BlockType::AllocLast(std::move(block), layout);
  } else {
    return BlockType::AllocFirst(std::move(block), layout);
  }
}
 
}  // namespace pw::allocator