HashBackendBuffer.h

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// -                        Open3D: www.open3d.org                            -
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// The MIT License (MIT)
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#pragma once

#include <assert.h>

#include <atomic>
#include <memory>
#include <vector>

#include "open3d/core/MemoryManager.h"
#include "open3d/core/Tensor.h"

namespace open3d {
namespace core {

void CPUResetHeap(Tensor &heap);

#ifdef BUILD_CUDA_MODULE
void CUDAResetHeap(Tensor &heap);
#endif

// The heap array stores the indices of the key/values buffers. It is not
// injective.
// During Allocate, an buffer index (buf_index) is extracted from the
// heap; During Free, a buf_index is put back to the top of the heap.
// ---------------------------------------------------------------------
// heap  ---Malloc-->  heap  ---Malloc-->  heap  ---Free(0)-->  heap
// N-1                 N-1                  N-1                  N-1   |
//  .                   .                    .                    .    |
//  .                   .                    .                    .    |
//  .                   .                    .                    .    |
//  3                   3                    3                    3    |
//  2                   2                    2 <-                 2    |
//  1                   1 <-                 1                    0 <- |
//  0 <- heap_top       0                    0                    0

// Buffer index type for the internal heap.
using buf_index_t = uint32_t;

class HashBackendBuffer {
public:
    struct HeapTop {
        Tensor cuda;
        std::atomic<int> cpu = {0};
    };

    HashBackendBuffer(int64_t capacity,
                      int64_t key_dsize,
                      std::vector<int64_t> value_dsizes,
                      const Device &device);

    void ResetHeap();

    Device GetDevice() const;

    int64_t GetCapacity() const;

    int64_t GetKeyDsize() const;

    std::vector<int64_t> GetValueDsizes() const;

    int64_t GetCommonBlockSize() const;

    std::vector<int64_t> GetValueBlocksPerElement() const;

    Tensor GetIndexHeap() const;

    HeapTop &GetHeapTop();

    int GetHeapTopIndex() const;

    Tensor GetKeyBuffer() const;

    std::vector<Tensor> GetValueBuffers() const;

    Tensor GetValueBuffer(size_t i = 0) const;

protected:
    Tensor heap_;
    HeapTop heap_top_;

    Tensor key_buffer_;
    std::vector<Tensor> value_buffers_;

    int64_t common_block_size_;
    std::vector<int64_t> blocks_per_element_;
};
}  // namespace core
}  // namespace open3d