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<p><a href="../index.html"><img src="title-21.png" width="253" height="39" alt="C++ Portable Types Library (PTypes) Version 2.1" border="0"></a>
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<p class="hpath"><a href="index.html">Top</a>: <a href="async.html">Multithreading</a>:
trigger</p>
<blockquote>
<pre class="lang">#include <pasync.h>
class trigger {
trigger(bool autoreset, bool initstate);
void wait();
void post();
void signal(); <span class="comment">// alias for post()</span>
void reset();
}
</pre>
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<p><span class="lang">Trigger</span> is a simple synchronization object typically
used to notify one or more threads about some event. <span class="lang">Trigger</span>
can be viewed as a simplified semaphore, which has only two states and does not
count the number of wait's and post's. Multiple threads can wait for an event
to occur; either one thread or all threads waiting on a trigger can be released
as soon as some other thread signals the <span class="lang">trigger</span> object.
Auto-reset triggers release only one thread each time <span class="lang">post()</span>
is called, and manual-reset triggers release all waiting threads at once. <span class="lang">Trigger</span>
mimics the Win32 Event object.</p>
<p><span class="def">trigger::trigger(bool autoreset, bool initstate)</span> creates
a trigger object with the initial state <span class="lang">initstate</span>. The
<span class="lang">autoreset</span> feature defines whether the trigger object
will automatically reset its state back to non-signaled when <span class="lang">post()</span>
is called.</p>
<p><span class="def">void trigger::wait()</span> waits until the state of the
trigger object becomes signaled, or returns immediately if the object is in signaled
state already.</p>
<p><span class="def">void trigger::post()</span> signals the trigger object. If
this is an auto-reset trigger, only one thread will be released and the state
of the object will be set to non-signaled. If this is a manual-reset trigger,
the state of the object is set to signaled and all threads waiting on the object
are being released. Subsequent calls to <span class="lang">wait()</span> from
any number of concurrent threads will return immediately.</p>
<p> <span class="def">void trigger::signal()</span> is an alias for <span class="lang">post()</span>.</p>
<p><span class="def">void trigger::reset()</span> resets the state of the trigger
object to non-signaled.</p>
<p class="seealso">See also: <a href="async.thread.html">thread</a>, <a href="async.mutex.html">mutex</a>,
<a href="async.rwlock.html">rwlock</a>, <a href="async.semaphore.html">semaphore</a>,
<a href="async.examples.html">Examples</a></p>
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