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<title>The GNU Fortran Compiler: _gfortran_caf_event_wait</title>
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<a name="g_t_005fgfortran_005fcaf_005fevent_005fwait"></a>
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Next: <a href="_005fgfortran_005fcaf_005fevent_005fquery.html#g_t_005fgfortran_005fcaf_005fevent_005fquery" accesskey="n" rel="next">_gfortran_caf_event_query</a>, Previous: <a href="_005fgfortran_005fcaf_005fevent_005fpost.html#g_t_005fgfortran_005fcaf_005fevent_005fpost" accesskey="p" rel="prev">_gfortran_caf_event_post</a>, Up: <a href="Function-ABI-Documentation.html#Function-ABI-Documentation" accesskey="u" rel="up">Function ABI Documentation</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<a name="g_t_005fgfortran_005fcaf_005fevent_005fwait-_002d_002d_002d-Wait-that-an-event-occurred"></a>
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<h4 class="subsection">8.2.13 <code>_gfortran_caf_event_wait</code> — Wait that an event occurred</h4>
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<a name="index-Coarray_002c-_005fgfortran_005fcaf_005fevent_005fwait"></a>
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<dl compact="compact">
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<dt><em>Description</em>:</dt>
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<dd><p>Wait until the event count has reached at least the specified
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<var>until_count</var>; if so, atomically decrement the event variable by this
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amount and return.
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</p>
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</dd>
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<dt><em>Syntax</em>:</dt>
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<dd><p><code>void _gfortran_caf_event_wait (caf_token_t token, size_t index,
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int until_count, int *stat, char *errmsg, int errmsg_len)</code>
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</p>
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</dd>
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<dt><em>Arguments</em>:</dt>
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<dd><table>
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<tr><td width="15%"><var>token</var></td><td width="70%">intent(in) An opaque pointer identifying the coarray.</td></tr>
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<tr><td width="15%"><var>index</var></td><td width="70%">Array index; first array index is 0. For scalars, it is
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always 0.</td></tr>
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<tr><td width="15%"><var>until_count</var></td><td width="70%">The number of events which have to be available
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before the function returns.</td></tr>
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<tr><td width="15%"><var>stat</var></td><td width="70%">intent(out) Stores the STAT=; may be NULL</td></tr>
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<tr><td width="15%"><var>errmsg</var></td><td width="70%">intent(out) When an error occurs, this will be set to
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an error message; may be NULL</td></tr>
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<tr><td width="15%"><var>errmsg_len</var></td><td width="70%">the buffer size of errmsg.</td></tr>
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</table>
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</dd>
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<dt><em>NOTES</em></dt>
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<dd><p>This function only operates on a local coarray. It acts like a loop checking
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atomically the value of the event variable, breaking if the value is greater
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or equal the requested number of counts. Before the function returns, the
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event variable has to be decremented by the requested <var>until_count</var> value.
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A possible implementation would be a busy loop for a certain number of spins
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(possibly depending on the number of threads relative to the number of available
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cores) followed by other waiting strategy such as a sleeping wait (possibly with
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an increasing number of sleep time) or, if possible, a futex wait.
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</p>
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<p>The statement is an image-control statement but does not imply sync memory.
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Still, all preceeding push communications to this image of images having
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issued a <code>event_push</code> have to be completed before this function returns.
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</p></dd>
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</dl>
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Next: <a href="_005fgfortran_005fcaf_005fevent_005fquery.html#g_t_005fgfortran_005fcaf_005fevent_005fquery" accesskey="n" rel="next">_gfortran_caf_event_query</a>, Previous: <a href="_005fgfortran_005fcaf_005fevent_005fpost.html#g_t_005fgfortran_005fcaf_005fevent_005fpost" accesskey="p" rel="prev">_gfortran_caf_event_post</a>, Up: <a href="Function-ABI-Documentation.html#Function-ABI-Documentation" accesskey="u" rel="up">Function ABI Documentation</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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