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| 26 | <a name="call_once"></a><div class="titlepage"></div> |
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| 27 | <div class="refnamediv"> |
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| 28 | <h2><span class="refentrytitle">Function call_once</span></h2> |
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| 29 | <p>boost::call_once — The <a href="call_once.html" title="Function call_once">call_once</a> function and |
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| 30 | <code class="computeroutput">once_flag</code> type (statically initialized to |
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| 31 | <a href="BOOST_ONCE_INIT.html" title="Macro BOOST_ONCE_INIT">BOOST_ONCE_INIT</a>) can be used to run a |
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| 32 | routine exactly once. This can be used to initialize data in a |
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| 33 | <a href="threads.html#threads.glossary.thread-safe">thread-safe</a> |
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| 34 | manner.</p> |
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| 35 | </div> |
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| 36 | <h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2> |
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| 37 | <div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"> |
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| 38 | call_once(<span class="bold"><strong>void</strong></span> (*func)() func, once_flag& flag);</pre></div> |
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| 39 | <div class="refsect1" lang="en"> |
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| 40 | <a name="id2782216"></a><h2>Description</h2> |
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| 41 | <p>Example usage is as follows:</p> |
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| 42 | <pre class="programlisting">//Example usage: |
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| 43 | boost::once_flag once = BOOST_ONCE_INIT; |
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| 44 | |
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| 45 | void init() |
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| 46 | { |
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| 47 | //... |
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| 48 | } |
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| 49 | |
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| 50 | void thread_proc() |
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| 51 | { |
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| 52 | boost::call_once(&init, once); |
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| 53 | }</pre> |
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| 54 | <p><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Requires</span></b>: |
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| 55 | |
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| 56 | The function <code class="computeroutput">func</code> shall not throw |
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| 57 | exceptions.<br><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Effects</span></b>: |
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| 58 | |
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| 59 | As if (in an atomic fashion): |
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| 60 | <code class="computeroutput">if (flag == BOOST_ONCE_INIT) func();</code><br><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Postconditions</span></b>: |
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| 61 | |
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| 62 | <code class="computeroutput">flag != BOOST_ONCE_INIT</code></p> |
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| 63 | </div> |
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| 67 | <td align="right"><small>Copyright © 2001-2003 William E. Kempf</small></td> |
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