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<a name="CUDA-Streams-Usage"></a>
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<a name="CUDA-Streams-Usage-1"></a>
<h2 class="chapter">7 CUDA Streams Usage</h2>

<p>This applies to the <code>nvptx</code> plugin only.
</p>
<p>The library provides elements that perform asynchronous movement of
data and asynchronous operation of computing constructs.  This
asynchronous functionality is implemented by making use of CUDA
streams<a name="DOCF1" href="#FOOT1"><sup>1</sup></a>.
</p>
<p>The primary means by that the asychronous functionality is accessed
is through the use of those OpenACC directives which make use of the
<code>async</code> and <code>wait</code> clauses.  When the <code>async</code> clause is
first used with a directive, it creates a CUDA stream.  If an
<code>async-argument</code> is used with the <code>async</code> clause, then the
stream is associated with the specified <code>async-argument</code>.
</p>
<p>Following the creation of an association between a CUDA stream and the
<code>async-argument</code> of an <code>async</code> clause, both the <code>wait</code>
clause and the <code>wait</code> directive can be used.  When either the
clause or directive is used after stream creation, it creates a
rendezvous point whereby execution waits until all operations
associated with the <code>async-argument</code>, that is, stream, have
completed.
</p>
<p>Normally, the management of the streams that are created as a result of
using the <code>async</code> clause, is done without any intervention by the
caller.  This implies the association between the <code>async-argument</code>
and the CUDA stream will be maintained for the lifetime of the program.
However, this association can be changed through the use of the library
function <code>acc_set_cuda_stream</code>.  When the function
<code>acc_set_cuda_stream</code> is called, the CUDA stream that was
originally associated with the <code>async</code> clause will be destroyed.
Caution should be taken when changing the association as subsequent
references to the <code>async-argument</code> refer to a different
CUDA stream.
</p>


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<h4 class="footnotes-heading">Footnotes</h4>

<h3><a name="FOOT1" href="#DOCF1">(1)</a></h3>
<p>See &quot;Stream Management&quot; in &quot;CUDA Driver API&quot;,
TRM-06703-001, Version 5.5, for additional information</p>
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