worst_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 WorstFitBlock = DetailedBlock<OffsetType, GenericFastSortedItem>;
 
template <typename BlockType = WorstFitBlock<uintptr_t>>
class WorstFitAllocator : public BlockAllocator<BlockType> {
 private:
  using SmallBucket = ReverseSortedBucket<BlockType>;
  using LargeBucket = ReverseFastSortedBucket<BlockType>;
 
 public:
  using Base = BlockAllocator<BlockType>;
 
  constexpr WorstFitAllocator() = default;
 
  WorstFitAllocator(ByteSpan region) { Base::Init(region); }
 
 private:
  size_t DoGetMaxAllocatable() override;
 
  BlockResult<BlockType> ChooseBlock(Layout layout) override;
 
  void ReserveBlock(BlockType& block) override;
 
  void RecycleBlock(BlockType& block) override;
 
  SmallBucket small_bucket_;
  LargeBucket large_bucket_;
};
 
 
// Template method implementations.
 
template <typename BlockType>
size_t WorstFitAllocator<BlockType>::DoGetMaxAllocatable() {
  const BlockType* largest = large_bucket_.empty()
                                 ? small_bucket_.FindLargest()
                                 : large_bucket_.FindLargest();
  return largest == nullptr ? 0 : largest->InnerSize();
}
 
template <typename BlockType>
BlockResult<BlockType> WorstFitAllocator<BlockType>::ChooseBlock(
    Layout layout) {
  BlockType* block = large_bucket_.RemoveCompatible(layout);
  if (block != nullptr) {
    return BlockType::AllocFirst(std::move(block), layout);
  }
  block = small_bucket_.RemoveCompatible(layout);
  if (block != nullptr) {
    return BlockType::AllocFirst(std::move(block), layout);
  }
  return BlockResult<BlockType>(nullptr, Status::NotFound());
}
 
template <typename BlockType>
void WorstFitAllocator<BlockType>::ReserveBlock(BlockType& block) {
  // The small bucket is slower; skip it if we can.
  if (!large_bucket_.Remove(block)) {
    std::ignore = small_bucket_.Remove(block);
  }
}
 
template <typename BlockType>
void WorstFitAllocator<BlockType>::RecycleBlock(BlockType& block) {
  if (block.InnerSize() < sizeof(typename LargeBucket::ItemType)) {
    std::ignore = small_bucket_.Add(block);
  } else {
    std::ignore = large_bucket_.Add(block);
  }
}
 
}  // namespace pw::allocator