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    <title>atomic_exchange, atomic_exchange_explicit</title>
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      <a id="id-1"></a>
      <div class="titlepage"></div>
      <div xmlns="" class="refnamediv">
        <a xmlns="http://www.w3.org/1999/xhtml" id="atomic_exchange"></a>
        <h1>atomic_exchange, atomic_exchange_explicit</h1>
        <p>
            Atomically replace the value pointed to by <code xmlns="http://www.w3.org/1999/xhtml" class="varname">object</code> with <code xmlns="http://www.w3.org/1999/xhtml" class="varname">desired</code>.
        </p>
      </div>
      <div class="refsynopsisdiv">
        <h2></h2>
        <div class="funcsynopsis">
          <table xmlns="" border="0" summary="Function synopsis" cellspacing="0" cellpadding="0">
            <tr valign="bottom">
              <td>
                <code xmlns="http://www.w3.org/1999/xhtml" class="funcdef">
                    C 
                    <strong class="fsfunc">atomic_exchange</strong>
                (</code>
                <td>volatile A  <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">*object</var>, </td>
              </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td>C  <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">desired</var><code>)</code></td>
            </tr>
          </table>
        </div>
        <div class="funcsynopsis">
          <table xmlns="" border="0" summary="Function synopsis" cellspacing="0" cellpadding="0">
            <tr valign="bottom">
              <td>
                <code xmlns="http://www.w3.org/1999/xhtml" class="funcdef">
                    C 
                    <strong class="fsfunc">atomic_exchange_explicit</strong>
                (</code>
                <td>volatile A  <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">*object</var>, </td>
              </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td>C  <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">desired</var>, </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td><a xmlns="http://www.w3.org/1999/xhtml" class="link" href="memory_order.html" target="pagedisplay">memory_order</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">order</var><code>)</code></td>
            </tr>
          </table>
        </div>
        <div class="funcsynopsis">
          <table xmlns="" border="0" summary="Function synopsis" cellspacing="0" cellpadding="0">
            <tr valign="bottom">
              <td>
                <code xmlns="http://www.w3.org/1999/xhtml" class="funcdef">
                    C 
                    <strong class="fsfunc">atomic_exchange_explicit</strong>
                (</code>
                <td>volatile A  <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">*object</var>, </td>
              </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td>C  <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">desired</var>, </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td><a xmlns="http://www.w3.org/1999/xhtml" class="link" href="memory_order.html" target="pagedisplay">memory_order</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">order</var>, </td>
            </tr>
            <tr valign="top">
              <td> </td>
              <td><a xmlns="http://www.w3.org/1999/xhtml" class="link" href="memory_scope.html" target="pagedisplay">memory_scope</a> <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">scope</var><code>)</code></td>
            </tr>
          </table>
        </div>
      </div>
      <div class="refsect1">
        <a id="parameters"></a>
        <h2>Parameters</h2>
        <div class="variablelist">
          <dl class="variablelist">
            <dt>
              <span class="term">
                <code class="varname">object</code>
              </span>
            </dt>
            <dd></dd>
            <dt>
              <span class="term">
                <code class="varname">desired</code>
              </span>
            </dt>
            <dd></dd>
            <dt>
              <span class="term">
                <code class="varname">order</code>
              </span>
            </dt>
            <dd></dd>
            <dt>
              <span class="term">
                <code class="varname">scope</code>
              </span>
            </dt>
            <dd></dd>
          </dl>
        </div>
      </div>
      <div class="refsect1">
        <a id="description"></a>
        <h2>Description</h2>
        <p>
            Atomically replace the value pointed to by 
            <code class="varname">object</code> with <code class="varname">desired</code>. 
            Memory is affected 
            according to the value of <code class="varname">order</code>. 
            These operations are read-modify-write operations (as defined 
            by section 5.1.2.4 of the C11 specification). 
            Atomically returns the value pointed to by 
            <code class="varname">object</code>
            immediately before the effects.
        </p>
        <p>
        In these operation definitions:
    </p>
        <p>
      </p>
        <div class="itemizedlist">
          <ul class="itemizedlist" style="list-style-type: disc; ">
            <li class="listitem">
            An <code class="code">A</code> refers to one of the atomic types.
        </li>
            <li class="listitem">
            A <code class="code">C</code> refers to its corresponding non-atomic type.
        </li>
            <li class="listitem">
            An <code class="code">M</code> refers to the type of the other 
            argument for arithmetic operations. For atomic 
            integer types, <code class="code">M</code> is <code class="code">C</code>.
        </li>
            <li class="listitem">
            The functions not ending in explicit have the same semantics as the corresponding
            explicit function with <code class="constant">memory_order_seq_cst</code> 
            for the <code class="code">memory_order</code> argument.
        </li>
            <li class="listitem">
            The functions that do not have <code class="code">memory_scope</code> 
            argument have the same semantics as 
            the corresponding functions with the <code class="code">memory_scope</code> argument set to
            <code class="constant">memory_scope_device</code>.
        </li>
          </ul>
        </div>
        <p>
    </p>
        <p>
        NOTE: With fine-grained system SVM, sharing 
        happens at the granularity of individual loads 
        and stores anywhere in host memory. Memory 
        consistency is always guaranteed at 
        synchronization points, but to obtain finer 
        control over consistency, the OpenCL atomics 
        functions may be used to ensure that the updates 
        to individual data values made by one unit of 
        execution are visible to other execution units. 
        In particular, when a host thread needs fine 
        control over the consistency of memory that is 
        shared with one or more OpenCL devices, it must 
        use atomic and fence operations that are 
        compatible with the C11 atomic operations.
    </p>
        <p>
        We can't require C11 atomics since host programs can 
        be implemented in other programming languages and 
        versions of C or C++, but we do require that the host 
        programs use atomics and that those atomics be compatible 
        with those in C11.
    </p>
        <h4><a id="id-1.6.7"></a>Restrictions</h4>
        <p>
        All operations on atomic types must be performed using the built-in atomic 
        functions. C11 and C++11 support operators on atomic types. OpenCL C does not 
        support operators with atomic types. Using atomic types with operators should result in a 
        compilation error.
    </p>
        <p>
        The <span class="type">atomic_bool</span>, <span class="type">atomic_char</span>, 
        <span class="type">atomic_uchar</span>, <span class="type">atomic_short</span>, 
        <span class="type">atomic_ushort</span>, <span class="type">atomic_intmax_t</span> 
        and <span class="type">atomic_uintmax_t</span> types are not 
        supported by OpenCL C.
    </p>
        <p>
        OpenCL C requires that the built-in atomic functions on 
        atomic types are lock-free.
    </p>
        <p>
        The <code class="code">_Atomic</code> type specifier and <code class="code">_Atomic</code> 
        type qualifier are not supported by OpenCL C.
    </p>
        <p>
        The behavior of atomic operations where pointer 
        arguments to the atomic functions refers 
        to an atomic type in the private address space is undefined.
    </p>
      </div>
      <div class="refsect1">
        <a id="specification"></a>
        <h2>Specification</h2>
        <p>
            <img src="pdficon_small1.gif" />
                                                 
            <a href="https://www.khronos.org/registry/cl/specs/opencl-2.0-openclc.pdf#namedest=atomic_exchange" target="OpenCL Spec">OpenCL Specification</a>
        </p>
      </div>
      <div class="refsect1">
        <a id="seealso"></a>
        <h2>Also see</h2>
        <p>
            <a class="citerefentry" href="atomicFunctions.html"><span class="citerefentry"><span class="refentrytitle">Atomic Functions</span></span></a>
        </p>
      </div>
      <div xmlns="" class="refsect3" lang="en" xml:lang="en"><a xmlns="http://www.w3.org/1999/xhtml" id="Copyright"></a><h4 xmlns="http://www.w3.org/1999/xhtml"></h4><img xmlns="http://www.w3.org/1999/xhtml" src="KhronosLogo.jpg" /><p xmlns="http://www.w3.org/1999/xhtml"></p>Copyright © 2007-2015 The Khronos Group Inc.
Permission is hereby granted, free of charge, to any person obtaining a
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"Materials"), to deal in the Materials without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Materials, and to
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