<div class="refentry" id="atomicCompSwap">

<div class="titlepage"></div>

<div class="refnamediv">

<h2>Name</h2>

<p>atomicCompSwap — perform an atomic compare-exchange operation to a variable</p>

</div>

<div class="refsynopsisdiv">

<h2>Declaration</h2>

<div class="funcsynopsis">

<table style="border: 0; cellspacing: 0; cellpadding: 0;" class="funcprototype-table">

<tr>

<td>

<code class="funcdef">int <strong class="fsfunc">atomicCompSwap</strong>(</code>

</td>

<td>inout int <var class="pdparam">mem</var>, </td>

</tr>

<tr>

<td> </td>

<td>uint <var class="pdparam">compare</var>, </td>

</tr>

<tr>

<td> </td>

<td>uint <var class="pdparam">data</var><code>)</code>;</td>

</tr>

</table>

<div class="funcprototype-spacer"> </div>

<table style="border: 0; cellspacing: 0; cellpadding: 0;" class="funcprototype-table">

<tr>

<td>

<code class="funcdef">uint <strong class="fsfunc">atomicCompSwap</strong>(</code>

</td>

<td>inout uint <var class="pdparam">mem</var>, </td>

</tr>

<tr>

<td> </td>

<td>uint <var class="pdparam">compare</var>, </td>

</tr>

<tr>

<td> </td>

<td>uint <var class="pdparam">data</var><code>)</code>;</td>

</tr>

</table>

<div class="funcprototype-spacer"> </div>

</div>

</div>

<div class="refsect1" id="parameters">

<h2>Parameters</h2>

<div class="variablelist">

<dl class="variablelist">

<dt>

<span class="term">

<em class="parameter">

<code>mem</code>

</em>

</span>

</dt>

<dd>

<p>

The variable to use as the target of the operation.

</p>

</dd>

<dt>

<span class="term">

<em class="parameter">

<code>data</code>

</em>

</span>

</dt>

<dd>

<p>

The data to be compared and potentially exchanged with <em class="parameter"><code>mem</code></em>.

</p>

</dd>

</dl>

</div>

</div>

<div class="refsect1" id="description">

<h2>Description</h2>

<p>

<code class="function">atomicCompSwap</code> performs an atomic comparison of <em class="parameter"><code>compare</code></em> with the contents of

<em class="parameter"><code>mem</code></em>. If the content of <em class="parameter"><code>mem</code></em> is equal to <em class="parameter"><code>compare</code></em>,

then the content of <em class="parameter"><code>data</code></em> is written into <em class="parameter"><code>mem</code></em>,

otherwise the content of <em class="parameter"><code>mem</code></em> is unmodifed.

The function returns the original content of <em class="parameter"><code>mem</code></em> regardless of the

outcome of the comparison. The contents of the memory being updated by the atomic operation are

guaranteed not to be modified by any other assignment or atomic memory function in any shader

invocation between the time the original value is read and the time the new value is written.

</p>

<p>

Atomic memory functions are supported only for a limited set of variables. A shader will fail to compile

if the value passed to the mem argument of an atomic memory function does not correspond to a buffer or

shared variable. It is acceptable to pass an element of an array or a single component of a vector to the

mem argument of an atomic memory function, as long as the underlying array or vector is a buffer or

shared variable.

</p>

</div>

{$pipelinestall}{$examples}

<div class="refsect1" id="versions">

<h2>Version Support</h2>

<div class="informaltable">

<table style="border-collapse: collapse; border-top: 2px solid ; border-bottom: 2px solid ; border-left: 2px solid ; border-right: 2px solid ; ">

<colgroup>

<col style="text-align: left; "/>

<col style="text-align: center; " class="firstvers"/>

<col style="text-align: center; "/>

<col style="text-align: center; "/>

<col style="text-align: center; "/>

<col style="text-align: center; "/>

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<col style="text-align: center; "/>

<col style="text-align: center; "/>

<col style="text-align: center; "/>

<col style="text-align: center; "/>

<col style="text-align: center; "/>

<col style="text-align: center; " class="lastvers"/>

</colgroup>

<thead>

<tr>

<th style="text-align: left; border-right: 2px solid ; ">

</th>

<th style="text-align: center; border-bottom: 2px solid ; " colspan="12">

<span class="bold"><strong>OpenGL Shading Language Version</strong></span>

</th>

</tr>

<tr>

<th style="text-align: left; border-right: 2px solid ; border-bottom: 2px solid ; ">

<span class="bold"><strong>Function Name</strong></span>

</th>

<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">

<span class="bold"><strong>1.10</strong></span>

</th>

<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">

<span class="bold"><strong>1.20</strong></span>

</th>

<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">

<span class="bold"><strong>1.30</strong></span>

</th>

<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">

<span class="bold"><strong>1.40</strong></span>

</th>

<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">

<span class="bold"><strong>1.50</strong></span>

</th>

<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">

<span class="bold"><strong>3.30</strong></span>

</th>

<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">

<span class="bold"><strong>4.00</strong></span>

</th>

<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">

<span class="bold"><strong>4.10</strong></span>

</th>

<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">

<span class="bold"><strong>4.20</strong></span>

</th>

<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">

<span class="bold"><strong>4.30</strong></span>

</th>

<th style="text-align: center; border-right: 2px solid ; border-bottom: 2px solid ; ">

<span class="bold"><strong>4.40</strong></span>

</th>

<th style="text-align: center; border-bottom: 2px solid ; ">

<span class="bold"><strong>4.50</strong></span>

</th>

</tr>

</thead>

<tbody>

<tr>

<td style="text-align: left; border-right: 2px solid ; ">atomicCompSwap</td>

<td style="text-align: center; border-right: 2px solid ; ">-</td>

<td style="text-align: center; border-right: 2px solid ; ">-</td>

<td style="text-align: center; border-right: 2px solid ; ">-</td>

<td style="text-align: center; border-right: 2px solid ; ">-</td>

<td style="text-align: center; border-right: 2px solid ; ">-</td>

<td style="text-align: center; border-right: 2px solid ; ">-</td>

<td style="text-align: center; border-right: 2px solid ; ">-</td>

<td style="text-align: center; border-right: 2px solid ; ">-</td>

<td style="text-align: center; border-right: 2px solid ; ">-</td>

<td style="text-align: center; border-right: 2px solid ; ">✔</td>

<td style="text-align: center; border-right: 2px solid ; ">✔</td>

<td style="text-align: center; ">✔</td>

</tr>

</tbody>

</table>

</div>

</div>

<div class="refsect1" id="seealso">

<h2>See Also</h2>

<p>

<a class="citerefentry" href="atomicAdd"><span class="citerefentry"><span class="refentrytitle">atomicAdd</span></span></a>,

<a class="citerefentry" href="atomicAnd"><span class="citerefentry"><span class="refentrytitle">atomicAnd</span></span></a>,

<a class="citerefentry" href="atomicOr"><span class="citerefentry"><span class="refentrytitle">atomicOr</span></span></a>,

<a class="citerefentry" href="atomicXor"><span class="citerefentry"><span class="refentrytitle">atomicXor</span></span></a>,

<a class="citerefentry" href="atomicMin"><span class="citerefentry"><span class="refentrytitle">atomicMin</span></span></a>,

<a class="citerefentry" href="atomicMax"><span class="citerefentry"><span class="refentrytitle">atomicMax</span></span></a>,

<a class="citerefentry" href="atomicExchange"><span class="citerefentry"><span class="refentrytitle">atomicExchange</span></span></a>

</p>

</div>

<div class="refsect1" id="Copyright">

<h2>Copyright</h2>

<p>

Copyright © 2011-2014 Khronos Group.

This material may be distributed subject to the terms and conditions set forth in

the Open Publication License, v 1.0, 8 June 1999.

<a class="link" href="https://opencontent.org/openpub/" target="_top">https://opencontent.org/openpub/</a>.

</p>

</div>

</div>