Streams

Stream is conceptually a queue of operations for a specific device. It is passed as an argument to all asynchronous operations like kernel launch, memory copy and allocations.

cuda::stream_ref

cuda::stream_ref is a non-owning wrapper around a cudaStream_t. It prevents unsafe implicit constructions from nullptr or integer literals and provides convenient helpers for:

• sync(): wait for the recorded work to complete

• is_done(): non-blocking completion query

• comparison operators against other stream_ref or cudaStream_t

Availability: CCCL 2.2.0 / CUDA 12.3

Example:

#include <cuda/stream>

cudaStream_t stream;
cudaStreamCreate(&stream);
cuda::stream_ref ref{stream};

ref.sync();            // synchronizes the stream via cudaStreamSynchronize
assert(ref.is_done()); // verifies that the stream has finished all operations via cudaStreamQuery

// compare against other stream_ref or cudaStream_t
assert(ref == stream);
assert(ref != cuda::invalid_stream);

cudaStreamDestroy(stream);

cuda::stream

cuda::stream is an owning wrapper around a cudaStream_t that manages the lifetime of the underlying CUDA stream. It derives from stream_ref, provides all of its functionality, and can be used anywhere a stream_ref is expected. It can be constructed for a specific cuda::device_ref, moved (but not copied), and converted from or to a cudaStream_t via from_native_handle/release().

Availability: CCCL 3.1.0 / CUDA 13.1

#include <cuda/stream>
#include <cuda/devices>

int main() {
  {
    // Create a stream on a specific device
    cuda::stream s{cuda::devices[0]};

   // Pass to a stream-ordered API

    // Synchronize the stream
    s.sync();
  } // Stream is automatically destroyed here
}