PoC: Share CUcontext

This commit enables Primary Device Context option when creating CUDA device context.
This will allow to share the device context with PyTorch, thus reduces the memory
usage (450+MB).

TODO:
- clean up the dlopen logic.
- handle the case where the primary device context is not yet initialized.

torchaudio/csrc/ffmpeg/hw_context.cpp

@@ -1,4 +1,7 @@
 #include <torchaudio/csrc/ffmpeg/hw_context.h>
+#include <cuda_runtime.h>
+#include <ATen/DynamicLibrary.h>
+#include <libavutil/hwcontext_cuda.h>
 
 namespace torchaudio::io {
 namespace {
@@ -8,15 +11,49 @@ static std::map<int, AVBufferRefPtr> CUDA_CONTEXT_CACHE;
 
 } // namespace
 
+CUresult (*cuDeviceGet_) (CUdevice*, int) = nullptr;
+CUresult (*cuDevicePrimaryCtxGetState_) (CUdevice, unsigned int*, int*) = nullptr;
+
+  #define CUDA_CHECK(X)                                   \
+  do {                                                  \
+    auto result = X;                                    \
+    if (result != CUDA_SUCCESS) {                        \
+      fprintf(                                          \
+          stderr,                                       \
+          "File %s Line %d %s returned %d.\n",          \
+          __FILE__,                                     \
+          __LINE__,                                     \
+          #X,X);                                        \
+      abort();                                          \
+    }                                                   \
+  } while (0)
+
 AVBufferRef* get_cuda_context(int index) {
   std::lock_guard<std::mutex> lock(MUTEX);
   if (index == -1) {
     index = 0;
   }
   if (CUDA_CONTEXT_CACHE.count(index) == 0) {
     AVBufferRef* p = nullptr;
+    std::cerr << "CREATING CUDA CONTEXT" << std::endl;
+
+    AVDictionary* opt = nullptr;
+    av_dict_set(&opt, "primary_ctx", "1", 0);
+
+    at::DynamicLibrary cuda{"libcuda.so.1"};
+
+    cuDeviceGet_ = (decltype(cuDeviceGet_))cuda.sym("cuDeviceGet");
+    cuDevicePrimaryCtxGetState_ = (decltype(cuDevicePrimaryCtxGetState_))cuda.sym("cuDevicePrimaryCtxGetState");
+
+    CUdevice device;
+    CUDA_CHECK(cuDeviceGet_(&device, index));
+
+    int dev_active = 0;
+    unsigned int dev_flags = 0;
+    CUDA_CHECK(cuDevicePrimaryCtxGetState_(device, &dev_flags, &dev_active));
+
     int ret = av_hwdevice_ctx_create(
-        &p, AV_HWDEVICE_TYPE_CUDA, std::to_string(index).c_str(), nullptr, 0);
+        &p, AV_HWDEVICE_TYPE_CUDA, std::to_string(index).c_str(), opt, dev_flags);
     TORCH_CHECK(
         ret >= 0,
         "Failed to create CUDA device context on device ",
@@ -26,6 +63,11 @@ AVBufferRef* get_cuda_context(int index) {
         ")");
     assert(p);
     CUDA_CONTEXT_CACHE.emplace(index, p);
+
+    AVHWDeviceContext *device_ctx = (AVHWDeviceContext*)p->data;
+    AVCUDADeviceContext *cuda_ctx = (AVCUDADeviceContext*)device_ctx->hwctx;
+    std::cerr << "CUcontext:" << cuda_ctx->cuda_ctx << std::endl;
+    std::cerr << "CUstream:" << cuda_ctx->stream << std::endl;
     return p;
   }
   AVBufferRefPtr& buffer = CUDA_CONTEXT_CACHE.at(index);