flow_stack_memory_resource.h

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#pragma once
#include "flow_memory_algorithm.h"
#include "flow_memory_resource.h"
#include <cassert>
#include <cstddef>
#include <exception>
 
namespace flow {

  class StackMemoryResource : public MemoryResource {
  public:
    explicit StackMemoryResource(void* buffer, std::size_t capacity) noexcept
      : buffer_(buffer), capacity_(capacity) {
    }
 
  protected:
    struct Header {
      void* oldBuffer;
    };
 
    void* buffer_;
    std::size_t capacity_;
 
    virtual void* allocateImp(std::size_t bytes, std::size_t alignment) override {
      void* oldBuffer = buffer_;
 
      void* alignedHeader = flow::alignWithHeader<Header>(alignment, bytes, buffer_, capacity_);
      if (!alignedHeader) {
        throw std::bad_alloc();
      }
 
      new (alignedHeader) Header(oldBuffer);
      void* allocatedBlock = reinterpret_cast<Header*>(alignedHeader) + 1;
      buffer_ = reinterpret_cast<std::byte*>(allocatedBlock) + bytes;
      capacity_ -= sizeof(Header) + bytes;
      return allocatedBlock;
    }
 
    virtual void deallocateImp(void* address, std::size_t bytes, [[maybe_unused]] std::size_t alignment) override {
      // TODO: assert address is the top most valid address
      assert(address == nullptr || address <= buffer_);
      if (!address) {
        return;
      }
 
      Header* header = reinterpret_cast<Header*>(address) - 1;
      std::size_t padding = pointerDistance(header->oldBuffer, header);
      buffer_ = header->oldBuffer;
      capacity_ += padding + sizeof(Header) + bytes;
      header->~Header();
    }
  };
}