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<title>Acquire a semaphore</title>
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<div class="refnamediv">
<h1 class="refname">sem_acquire</h1>
<p class="verinfo">(PHP 4, PHP 5, PHP 7)</p><p class="refpurpose"><span class="refname">sem_acquire</span> — <span class="dc-title">Acquire a semaphore</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.sem-acquire-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type">bool</span> <span class="methodname"><strong>sem_acquire</strong></span>
( <span class="methodparam"><span class="type">resource</span> <code class="parameter">$sem_identifier</code></span>
[, <span class="methodparam"><span class="type">bool</span> <code class="parameter">$nowait</code><span class="initializer"> = <strong><code>FALSE</code></strong></span></span>
] )</div>
<p class="para rdfs-comment">
<span class="function"><strong>sem_acquire()</strong></span> by default blocks (if necessary) until the
semaphore can be acquired. A process attempting to acquire a semaphore which
it has already acquired will block forever if acquiring the semaphore would
cause its maximum number of semaphore to be exceeded.
</p>
<p class="para">
After processing a request, any semaphores acquired by the process but not
explicitly released will be released automatically and a warning will be
generated.
</p>
</div>
<div class="refsect1 parameters" id="refsect1-function.sem-acquire-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<code class="parameter">sem_identifier</code></dt>
<dd>
<p class="para">
<code class="parameter">sem_identifier</code> is a semaphore resource,
obtained from <span class="function"><a href="function.sem-get.html" class="function">sem_get()</a></span>.
</p>
</dd>
<dt>
<code class="parameter">nowait</code></dt>
<dd>
<p class="para">
Specifies if the process shouldn't wait for the semaphore to be acquired.
If set to <em>true</em>, the call will return
<em>false</em> immediately if a semaphore cannot be immediately
acquired.
</p>
</dd>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.sem-acquire-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
Returns <strong><code>TRUE</code></strong> on success or <strong><code>FALSE</code></strong> on failure.
</p>
</div>
<div class="refsect1 changelog" id="refsect1-function.sem-acquire-changelog">
<h3 class="title">Changelog</h3>
<p class="para">
<table class="doctable informaltable">
<thead>
<tr>
<th>Version</th>
<th>Description</th>
</tr>
</thead>
<tbody class="tbody">
<tr>
<td>5.6.1</td>
<td>
The <code class="parameter">$nowait</code> parameter was added.
</td>
</tr>
</tbody>
</table>
</p>
</div>
<div class="refsect1 seealso" id="refsect1-function.sem-acquire-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"><span class="function"><a href="function.sem-get.html" class="function" rel="rdfs-seeAlso">sem_get()</a> - Get a semaphore id</span></li>
<li class="member"><span class="function"><a href="function.sem-release.html" class="function" rel="rdfs-seeAlso">sem_release()</a> - Release a semaphore</span></li>
</ul>
</p>
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