ceres-solver/internal/ceres/cuda_buffer.h

// Ceres Solver - A fast non-linear least squares minimizer
// Copyright 2022 Google Inc. All rights reserved.
// http://ceres-solver.org/
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// Author: joydeepb@cs.utexas.edu (Joydeep Biswas)

#ifndef CERES_INTERNAL_CUDA_BUFFER_H_
#define CERES_INTERNAL_CUDA_BUFFER_H_

#include "ceres/internal/config.h"

#ifndef CERES_NO_CUDA

#include <vector>

#include "cuda_runtime.h"
#include "glog/logging.h"

// An encapsulated buffer to maintain GPU memory, and handle transfers between
// GPU and system memory. It is the responsibility of the user to ensure that
// the appropriate GPU device is selected before each subroutine is called. This
// is particularly important when using multiple GPU devices on different CPU
// threads, since active Cuda devices are determined by the cuda runtime on a
// per-thread basis. Note that unless otherwise specified, all methods use the
// default stream, and are synchronous.
template <typename T>
class CudaBuffer {
 public:
  CudaBuffer() = default;
  CudaBuffer(const CudaBuffer&) = delete;
  CudaBuffer& operator=(const CudaBuffer&) = delete;

  ~CudaBuffer() {
    if (data_ != nullptr) {
      CHECK_EQ(cudaFree(data_), cudaSuccess);
    }
  }

  // Grow the GPU memory buffer if needed to accommodate data of the specified
  // size
  void Reserve(const size_t size) {
    if (size > size_) {
      if (data_ != nullptr) {
        CHECK_EQ(cudaFree(data_), cudaSuccess);
      }
      CHECK_EQ(cudaMalloc(&data_, size * sizeof(T)), cudaSuccess);
      size_ = size;
    }
  }

  // Perform an asynchronous copy from CPU memory to GPU memory using the stream
  // provided.
  void CopyToGpuAsync(const T* data, const size_t size, cudaStream_t stream) {
    Reserve(size);
    CHECK_EQ(cudaMemcpyAsync(data_,
                             data,
                             size * sizeof(T),
                             cudaMemcpyHostToDevice,
                             stream),
             cudaSuccess);
  }

  // Copy data from the GPU to CPU memory. This is necessarily synchronous since
  // any potential GPU kernels that may be writing to the buffer must finish
  // before the transfer happens.
  void CopyToHost(T* data, const size_t size) {
    CHECK(data_ != nullptr);
    CHECK_EQ(cudaMemcpy(data, data_, size * sizeof(T), cudaMemcpyDeviceToHost),
             cudaSuccess);
  }

  void CopyToGpu(const std::vector<T>& data) {
    CopyToGpu(data.data(), data.size());
  }

  T* data() { return data_; }
  size_t size() const { return size_; }

 private:
  T* data_ = nullptr;
  size_t size_ = 0;
};

#endif  // CERES_NO_CUDA

#endif  // CERES_INTERNAL_CUDA_BUFFER_H_