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.. meta::
  :description: API reference for cuda::stream_ref, a type-safe wrapper around hipStream_t that prevents implicit conversions and provides wait and ready member functions in libhipcxx.
  :keywords: libhipcxx, ROCm, HIP, C++, stream_ref, hipStream_t, stream, wait, ready, implicit conversion

.. _libcudacxx-extended-api-streams-stream-ref:

``cuda::stream_ref``: a wrapper around a ``hipStream_t``
==========================================================

This page documents ``cuda::stream_ref``, a type-safe wrapper around ``hipStream_t`` that prevents implicit conversions and provides wait and ready member functions.

HIP `stream-ordered allocations <https://rocm.docs.amd.com/projects/HIP/en/latest/how-to/hip_runtime_api/memory_management/stream_ordered_allocator.html>`__
rely on ``hipStream_t`` as a handle to the HIP stream.

However, as this is just an alias for a plain pointer type it carries with it common pitfalls around implicit
conversions from, for example, ``nullptr`` or a literal ``0``.

These hard to spot bugs can be avoided through ``cuda::stream_ref``, which is a simple wrapper around a ``hipStream_t``
that prevents implicit conversions. It also provides the ``wait()`` and ``ready()`` member functions to facilitate
waiting for a stream to finish and checking whether it is finished.

.. code:: cpp

       hipStream_t stream;
       hipStreamCreate(&stream);
       cuda::stream_ref ref{stream};

       ref.wait();          // synchronizes the stream via hipStreamSynchronize
       assert(ref.ready()); // verifies that the stream has finished all operations via hipStreamQuery
       hipStreamDestroy(stream);