worst_fit_block_allocator.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 "pw_allocator/block_allocator.h"
 
namespace pw::allocator {
 
template <typename OffsetType = uintptr_t,
          size_t kPoisonInterval = 0,
          size_t kAlign = alignof(OffsetType)>
class WorstFitBlockAllocator
    : public BlockAllocator<OffsetType, kPoisonInterval, kAlign> {
 public:
  using Base = BlockAllocator<OffsetType, kPoisonInterval, kAlign>;
  using BlockType = typename Base::BlockType;
 
  constexpr WorstFitBlockAllocator() : Base() {}
 
  explicit WorstFitBlockAllocator(ByteSpan region) : Base(region) {}
 
 private:
  BlockType* ChooseBlock(Layout layout) override {
    // Search backwards for the biggest block that can hold this allocation.
    BlockType* worst = nullptr;
    for (auto* block : Base::rblocks()) {
      if (!block->CanAllocLast(layout).ok()) {
        continue;
      }
      if (worst == nullptr || block->OuterSize() > worst->OuterSize()) {
        worst = block;
      }
    }
    if (worst != nullptr && BlockType::AllocLast(worst, layout).ok()) {
      return worst;
    }
    return nullptr;
  }
};
 
}  // namespace pw::allocator