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   <div id="projectname">libevent
   &#160;<span id="projectnumber">2.2.1</span>
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   <div id="projectbrief">Event notification library</div>
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<li class="navelem"><a class="el" href="dir_db160b4728e6067cf5f9cc14ec42c79d.html">event2</a></li>  </ul>
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<a href="#typedef-members">Typedefs</a> &#124;
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<p>"Prepare" and "check" watchers.  
<a href="#details">More...</a></p>
<div class="textblock"><code>#include &lt;event2/visibility.h&gt;</code><br />
</div>
<p><a href="watch_8h_source.html">Go to the source code of this file.</a></p>
<table class="memberdecls">
<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="typedef-members"></a>
Typedefs</h2></td></tr>
<tr class="memitem:a552db1e01295811adc2191580a48f3f7"><td class="memItemLeft" align="right" valign="top">typedef void(*&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="watch_8h.html#a552db1e01295811adc2191580a48f3f7">evwatch_check_cb</a>) (struct evwatch *, const struct evwatch_check_cb_info *, void *)</td></tr>
<tr class="memdesc:a552db1e01295811adc2191580a48f3f7"><td class="mdescLeft">&#160;</td><td class="mdescRight">Check callback, invoked by event_base_loop immediately after polling for I/O and before processing any active events.  <a href="watch_8h.html#a552db1e01295811adc2191580a48f3f7">More...</a><br /></td></tr>
<tr class="separator:a552db1e01295811adc2191580a48f3f7"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:ab49b34b1552c9cc5e6a736cfc435c766"><td class="memItemLeft" align="right" valign="top">typedef void(*&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="watch_8h.html#ab49b34b1552c9cc5e6a736cfc435c766">evwatch_prepare_cb</a>) (struct evwatch *, const struct evwatch_prepare_cb_info *, void *)</td></tr>
<tr class="memdesc:ab49b34b1552c9cc5e6a736cfc435c766"><td class="mdescLeft">&#160;</td><td class="mdescRight">Prepare callback, invoked by event_base_loop immediately before polling for I/O.  <a href="watch_8h.html#ab49b34b1552c9cc5e6a736cfc435c766">More...</a><br /></td></tr>
<tr class="separator:ab49b34b1552c9cc5e6a736cfc435c766"><td class="memSeparator" colspan="2">&#160;</td></tr>
</table><table class="memberdecls">
<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="func-members"></a>
Functions</h2></td></tr>
<tr class="memitem:a12f916b5846e7925939abbaca49b4521"><td class="memItemLeft" align="right" valign="top">EVENT2_EXPORT_SYMBOL struct <a class="el" href="structevent__base.html">event_base</a> *&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="watch_8h.html#a12f916b5846e7925939abbaca49b4521">evwatch_base</a> (struct evwatch *watcher)</td></tr>
<tr class="memdesc:a12f916b5846e7925939abbaca49b4521"><td class="mdescLeft">&#160;</td><td class="mdescRight">Get the <a class="el" href="structevent__base.html" title="Structure to hold information and state for a Libevent dispatch loop.">event_base</a> that a given evwatch is registered with.  <a href="watch_8h.html#a12f916b5846e7925939abbaca49b4521">More...</a><br /></td></tr>
<tr class="separator:a12f916b5846e7925939abbaca49b4521"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:acfeaa9fc345062e41c7f807d6c5d511f"><td class="memItemLeft" align="right" valign="top">EVENT2_EXPORT_SYMBOL struct evwatch *&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="watch_8h.html#acfeaa9fc345062e41c7f807d6c5d511f">evwatch_check_new</a> (struct <a class="el" href="structevent__base.html">event_base</a> *base, <a class="el" href="watch_8h.html#a552db1e01295811adc2191580a48f3f7">evwatch_check_cb</a> callback, void *arg)</td></tr>
<tr class="memdesc:acfeaa9fc345062e41c7f807d6c5d511f"><td class="mdescLeft">&#160;</td><td class="mdescRight">Register a new "check" watcher, to be called in the event loop after polling for events and before handling them.  <a href="watch_8h.html#acfeaa9fc345062e41c7f807d6c5d511f">More...</a><br /></td></tr>
<tr class="separator:acfeaa9fc345062e41c7f807d6c5d511f"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:aadf0c377890835ae40612b19f9029032"><td class="memItemLeft" align="right" valign="top">EVENT2_EXPORT_SYMBOL void&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="watch_8h.html#aadf0c377890835ae40612b19f9029032">evwatch_free</a> (struct evwatch *watcher)</td></tr>
<tr class="memdesc:aadf0c377890835ae40612b19f9029032"><td class="mdescLeft">&#160;</td><td class="mdescRight">Deregister and deallocate a watcher.  <a href="watch_8h.html#aadf0c377890835ae40612b19f9029032">More...</a><br /></td></tr>
<tr class="separator:aadf0c377890835ae40612b19f9029032"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:a5f7837d8af2b00c9ec401e00b4f33781"><td class="memItemLeft" align="right" valign="top">EVENT2_EXPORT_SYMBOL int&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="watch_8h.html#a5f7837d8af2b00c9ec401e00b4f33781">evwatch_prepare_get_timeout</a> (const struct evwatch_prepare_cb_info *info, struct timeval *timeout)</td></tr>
<tr class="memdesc:a5f7837d8af2b00c9ec401e00b4f33781"><td class="mdescLeft">&#160;</td><td class="mdescRight">Get the timeout (the expected polling duration) passed to the underlying implementation's <code>dispatch</code>.  <a href="watch_8h.html#a5f7837d8af2b00c9ec401e00b4f33781">More...</a><br /></td></tr>
<tr class="separator:a5f7837d8af2b00c9ec401e00b4f33781"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:ad446340d54b8de7125cae9d5fed9c61e"><td class="memItemLeft" align="right" valign="top">EVENT2_EXPORT_SYMBOL struct evwatch *&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="watch_8h.html#ad446340d54b8de7125cae9d5fed9c61e">evwatch_prepare_new</a> (struct <a class="el" href="structevent__base.html">event_base</a> *base, <a class="el" href="watch_8h.html#ab49b34b1552c9cc5e6a736cfc435c766">evwatch_prepare_cb</a> callback, void *arg)</td></tr>
<tr class="memdesc:ad446340d54b8de7125cae9d5fed9c61e"><td class="mdescLeft">&#160;</td><td class="mdescRight">Register a new "prepare" watcher, to be called in the event loop prior to polling for events.  <a href="watch_8h.html#ad446340d54b8de7125cae9d5fed9c61e">More...</a><br /></td></tr>
<tr class="separator:ad446340d54b8de7125cae9d5fed9c61e"><td class="memSeparator" colspan="2">&#160;</td></tr>
</table>
<a name="details" id="details"></a><h2 class="groupheader">Detailed Description</h2>
<div class="textblock"><p>"Prepare" and "check" watchers. </p>
<p>"Prepare" and "check" watchers. A "prepare" watcher is a callback that fires immediately before polling for I/O. A "check" watcher is a callback that fires immediately after polling and before processing any active events. This may be useful for embedding other libraries' event loops (e.g. UI toolkits) into libevent's. </p>
</div><h2 class="groupheader">Typedef Documentation</h2>
<a id="a552db1e01295811adc2191580a48f3f7"></a>
<h2 class="memtitle"><span class="permalink"><a href="#a552db1e01295811adc2191580a48f3f7">&#9670;&nbsp;</a></span>evwatch_check_cb</h2>

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<div class="memproto">
      <table class="memname">
        <tr>
          <td class="memname">typedef void(* evwatch_check_cb) (struct evwatch *, const struct evwatch_check_cb_info *, void *)</td>
        </tr>
      </table>
</div><div class="memdoc">

<p>Check callback, invoked by event_base_loop immediately after polling for I/O and before processing any active events. </p>
<dl class="params"><dt>Parameters</dt><dd>
  <table class="params">
    <tr><td class="paramname">watcher</td><td>the check watcher that invoked this callback. </td></tr>
    <tr><td class="paramname">info</td><td>contextual information passed from event_base_loop. </td></tr>
    <tr><td class="paramname">arg</td><td>additional user-defined argument, set in <code>evwatch_check_new</code>. </td></tr>
  </table>
  </dd>
</dl>

</div>
</div>
<a id="ab49b34b1552c9cc5e6a736cfc435c766"></a>
<h2 class="memtitle"><span class="permalink"><a href="#ab49b34b1552c9cc5e6a736cfc435c766">&#9670;&nbsp;</a></span>evwatch_prepare_cb</h2>

<div class="memitem">
<div class="memproto">
      <table class="memname">
        <tr>
          <td class="memname">typedef void(* evwatch_prepare_cb) (struct evwatch *, const struct evwatch_prepare_cb_info *, void *)</td>
        </tr>
      </table>
</div><div class="memdoc">

<p>Prepare callback, invoked by event_base_loop immediately before polling for I/O. </p>
<dl class="params"><dt>Parameters</dt><dd>
  <table class="params">
    <tr><td class="paramname">watcher</td><td>the prepare watcher that invoked this callback. </td></tr>
    <tr><td class="paramname">info</td><td>contextual information passed from event_base_loop. </td></tr>
    <tr><td class="paramname">arg</td><td>additional user-defined argument, set in <code>evwatch_prepare_new</code>. </td></tr>
  </table>
  </dd>
</dl>

</div>
</div>
<h2 class="groupheader">Function Documentation</h2>
<a id="a12f916b5846e7925939abbaca49b4521"></a>
<h2 class="memtitle"><span class="permalink"><a href="#a12f916b5846e7925939abbaca49b4521">&#9670;&nbsp;</a></span>evwatch_base()</h2>

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      <table class="memname">
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          <td class="memname">EVENT2_EXPORT_SYMBOL struct <a class="el" href="structevent__base.html">event_base</a>* evwatch_base </td>
          <td>(</td>
          <td class="paramtype">struct evwatch *&#160;</td>
          <td class="paramname"><em>watcher</em></td><td>)</td>
          <td></td>
        </tr>
      </table>
</div><div class="memdoc">

<p>Get the <a class="el" href="structevent__base.html" title="Structure to hold information and state for a Libevent dispatch loop.">event_base</a> that a given evwatch is registered with. </p>
<dl class="params"><dt>Parameters</dt><dd>
  <table class="params">
    <tr><td class="paramname">watcher</td><td>the watcher to get the <a class="el" href="structevent__base.html" title="Structure to hold information and state for a Libevent dispatch loop.">event_base</a> for. </td></tr>
  </table>
  </dd>
</dl>
<dl class="section return"><dt>Returns</dt><dd>the <a class="el" href="structevent__base.html" title="Structure to hold information and state for a Libevent dispatch loop.">event_base</a> for the given watcher. </dd></dl>

</div>
</div>
<a id="acfeaa9fc345062e41c7f807d6c5d511f"></a>
<h2 class="memtitle"><span class="permalink"><a href="#acfeaa9fc345062e41c7f807d6c5d511f">&#9670;&nbsp;</a></span>evwatch_check_new()</h2>

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<div class="memproto">
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          <td class="memname">EVENT2_EXPORT_SYMBOL struct evwatch* evwatch_check_new </td>
          <td>(</td>
          <td class="paramtype">struct <a class="el" href="structevent__base.html">event_base</a> *&#160;</td>
          <td class="paramname"><em>base</em>, </td>
        </tr>
        <tr>
          <td class="paramkey"></td>
          <td></td>
          <td class="paramtype"><a class="el" href="watch_8h.html#a552db1e01295811adc2191580a48f3f7">evwatch_check_cb</a>&#160;</td>
          <td class="paramname"><em>callback</em>, </td>
        </tr>
        <tr>
          <td class="paramkey"></td>
          <td></td>
          <td class="paramtype">void *&#160;</td>
          <td class="paramname"><em>arg</em>&#160;</td>
        </tr>
        <tr>
          <td></td>
          <td>)</td>
          <td></td><td></td>
        </tr>
      </table>
</div><div class="memdoc">

<p>Register a new "check" watcher, to be called in the event loop after polling for events and before handling them. </p>
<p>Watchers will be called in the order they were registered.</p>
<dl class="params"><dt>Parameters</dt><dd>
  <table class="params">
    <tr><td class="paramname">base</td><td>the <a class="el" href="structevent__base.html" title="Structure to hold information and state for a Libevent dispatch loop.">event_base</a> to operate on. </td></tr>
    <tr><td class="paramname">callback</td><td>the callback function to invoke. </td></tr>
    <tr><td class="paramname">arg</td><td>additional user-defined argument provided to the callback. </td></tr>
  </table>
  </dd>
</dl>
<dl class="section return"><dt>Returns</dt><dd>a pointer to the newly allocated event watcher. </dd></dl>

</div>
</div>
<a id="aadf0c377890835ae40612b19f9029032"></a>
<h2 class="memtitle"><span class="permalink"><a href="#aadf0c377890835ae40612b19f9029032">&#9670;&nbsp;</a></span>evwatch_free()</h2>

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          <td class="memname">EVENT2_EXPORT_SYMBOL void evwatch_free </td>
          <td>(</td>
          <td class="paramtype">struct evwatch *&#160;</td>
          <td class="paramname"><em>watcher</em></td><td>)</td>
          <td></td>
        </tr>
      </table>
</div><div class="memdoc">

<p>Deregister and deallocate a watcher. </p>
<p>Any watchers not freed using evwatch_free will eventually be deallocated in event_base_free (calling evwatch_free on a watcher after event_base_free has been called on its corresponding <a class="el" href="structevent__base.html" title="Structure to hold information and state for a Libevent dispatch loop.">event_base</a> is an error).</p>
<dl class="params"><dt>Parameters</dt><dd>
  <table class="params">
    <tr><td class="paramname">watcher</td><td>the watcher to deregister and deallocate. </td></tr>
  </table>
  </dd>
</dl>

</div>
</div>
<a id="a5f7837d8af2b00c9ec401e00b4f33781"></a>
<h2 class="memtitle"><span class="permalink"><a href="#a5f7837d8af2b00c9ec401e00b4f33781">&#9670;&nbsp;</a></span>evwatch_prepare_get_timeout()</h2>

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          <td class="memname">EVENT2_EXPORT_SYMBOL int evwatch_prepare_get_timeout </td>
          <td>(</td>
          <td class="paramtype">const struct evwatch_prepare_cb_info *&#160;</td>
          <td class="paramname"><em>info</em>, </td>
        </tr>
        <tr>
          <td class="paramkey"></td>
          <td></td>
          <td class="paramtype">struct timeval *&#160;</td>
          <td class="paramname"><em>timeout</em>&#160;</td>
        </tr>
        <tr>
          <td></td>
          <td>)</td>
          <td></td><td></td>
        </tr>
      </table>
</div><div class="memdoc">

<p>Get the timeout (the expected polling duration) passed to the underlying implementation's <code>dispatch</code>. </p>
<p>This value will only be set if there are pending EV_TIMEOUT events and if the <a class="el" href="structevent__base.html" title="Structure to hold information and state for a Libevent dispatch loop.">event_base</a> isn't in EVLOOP_NONBLOCK mode. It may be a useful performance statistic to compare the expected polling duration against the actual polling duration (that is, the time difference measured between this prepare callback and the following check callback).</p>
<dl class="params"><dt>Parameters</dt><dd>
  <table class="params">
    <tr><td class="paramname">info</td><td>the "prepare" callback info. </td></tr>
    <tr><td class="paramname">timeout</td><td>address of a timeval to write the polling duration to. </td></tr>
  </table>
  </dd>
</dl>
<dl class="section return"><dt>Returns</dt><dd>1 if a value was written to *timeout, or 0 if not. </dd></dl>

</div>
</div>
<a id="ad446340d54b8de7125cae9d5fed9c61e"></a>
<h2 class="memtitle"><span class="permalink"><a href="#ad446340d54b8de7125cae9d5fed9c61e">&#9670;&nbsp;</a></span>evwatch_prepare_new()</h2>

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          <td class="memname">EVENT2_EXPORT_SYMBOL struct evwatch* evwatch_prepare_new </td>
          <td>(</td>
          <td class="paramtype">struct <a class="el" href="structevent__base.html">event_base</a> *&#160;</td>
          <td class="paramname"><em>base</em>, </td>
        </tr>
        <tr>
          <td class="paramkey"></td>
          <td></td>
          <td class="paramtype"><a class="el" href="watch_8h.html#ab49b34b1552c9cc5e6a736cfc435c766">evwatch_prepare_cb</a>&#160;</td>
          <td class="paramname"><em>callback</em>, </td>
        </tr>
        <tr>
          <td class="paramkey"></td>
          <td></td>
          <td class="paramtype">void *&#160;</td>
          <td class="paramname"><em>arg</em>&#160;</td>
        </tr>
        <tr>
          <td></td>
          <td>)</td>
          <td></td><td></td>
        </tr>
      </table>
</div><div class="memdoc">

<p>Register a new "prepare" watcher, to be called in the event loop prior to polling for events. </p>
<p>Watchers will be called in the order they were registered.</p>
<dl class="params"><dt>Parameters</dt><dd>
  <table class="params">
    <tr><td class="paramname">base</td><td>the <a class="el" href="structevent__base.html" title="Structure to hold information and state for a Libevent dispatch loop.">event_base</a> to operate on. </td></tr>
    <tr><td class="paramname">callback</td><td>the callback function to invoke. </td></tr>
    <tr><td class="paramname">arg</td><td>additional user-defined argument provided to the callback. </td></tr>
  </table>
  </dd>
</dl>
<dl class="section return"><dt>Returns</dt><dd>a pointer to the newly allocated event watcher. </dd></dl>

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