src/dawn/native/d3d12/StagingDescriptorAllocatorD3D12.h

// Copyright 2020 The Dawn & Tint Authors
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#ifndef SRC_DAWN_NATIVE_D3D12_STAGINGDESCRIPTORALLOCATORD3D12_H_
#define SRC_DAWN_NATIVE_D3D12_STAGINGDESCRIPTORALLOCATORD3D12_H_

#include <vector>

#include "dawn/common/SerialQueue.h"
#include "dawn/native/Error.h"
#include "dawn/native/IntegerTypes.h"
#include "dawn/native/d3d12/CPUDescriptorHeapAllocationD3D12.h"

// |StagingDescriptorAllocator| allocates a fixed-size block of descriptors from a CPU
// descriptor heap pool.
// Internally, it manages a list of heaps using a fixed-size block allocator. The fixed-size
// block allocator is backed by a list of free blocks (free-list). The heap is in one of two
// states: AVAILABLE or not. To allocate, the next free block is removed from the free-list
// and the corresponding heap offset is returned. The AVAILABLE heap always has room for
// at-least one free block. If no AVAILABLE heap exists, a new heap is created and inserted
// back into the pool to be immediately used. To deallocate, the block corresponding to the
// offset is inserted back into the free-list.
namespace dawn::native::d3d12 {

class Device;

class StagingDescriptorAllocator {
  public:
    StagingDescriptorAllocator() = default;
    StagingDescriptorAllocator(Device* device,
                               uint32_t descriptorCount,
                               uint32_t heapSize,
                               D3D12_DESCRIPTOR_HEAP_TYPE heapType);
    ~StagingDescriptorAllocator();

    ResultOrError<CPUDescriptorHeapAllocation> AllocateCPUDescriptors();

    // Will call Deallocate when the serial is passed.
    ResultOrError<CPUDescriptorHeapAllocation> AllocateTransientCPUDescriptors();

    void Deallocate(CPUDescriptorHeapAllocation* allocation);

    uint32_t GetSizeIncrement() const;

    void Tick(ExecutionSerial completedSerial);

  private:
    using Index = uint16_t;

    struct NonShaderVisibleBuffer {
        ComPtr<ID3D12DescriptorHeap> heap;
        std::vector<Index> freeBlockIndices;
    };

    MaybeError AllocateCPUHeap();

    Index GetFreeBlockIndicesSize() const;

    std::vector<uint32_t> mAvailableHeaps;  // Indices into the pool.
    std::vector<NonShaderVisibleBuffer> mPool;

    Device const* mDevice = nullptr;

    const uint32_t mSizeIncrement = 0;  // Size of the descriptor (in bytes).
    const uint32_t mBlockSize = 0;      // Size of the block of descriptors (in bytes).
    const uint32_t mHeapSize = 0;       // Size of the heap (in number of descriptors).

    D3D12_DESCRIPTOR_HEAP_TYPE mHeapType;

    SerialQueue<ExecutionSerial, CPUDescriptorHeapAllocation> mAllocationsToDelete;
};

}  // namespace dawn::native::d3d12

#endif  // SRC_DAWN_NATIVE_D3D12_STAGINGDESCRIPTORALLOCATORD3D12_H_