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<!DOCTYPE html>
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Class: Concurrent::Semaphore
— Concurrent Ruby
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<div id="content"><h1>Class: Concurrent::Semaphore
</h1>
<div class="box_info">
<dl>
<dt>Inherits:</dt>
<dd>
<span class="inheritName"><span class='object_link'>SemaphoreImplementation</span></span>
<ul class="fullTree">
<li>Object</li>
<li class="next">Concurrent::Semaphore</li>
</ul>
<a href="#" class="inheritanceTree">show all</a>
</dd>
</dl>
<dl>
<dt>Defined in:</dt>
<dd>lib/concurrent/atomic/semaphore.rb</dd>
</dl>
</div>
<h2>Overview</h2><div class="docstring">
<div class="discussion">
<p>A counting semaphore. Conceptually, a semaphore maintains a set of
permits. Each <span class='object_link'><a href="#acquire-instance_method" title="Concurrent::Semaphore#acquire (method)">#acquire</a></span> blocks if necessary until a permit is
available, and then takes it. Each <span class='object_link'><a href="#release-instance_method" title="Concurrent::Semaphore#release (method)">#release</a></span> adds a permit, potentially
releasing a blocking acquirer.
However, no actual permit objects are used; the Semaphore just keeps a
count of the number available and acts accordingly.</p>
</div>
</div>
<div class="tags">
<div class="examples">
<p class="tag_title">Examples:</p>
<pre class="example code"><code><span class='id identifier rubyid_semaphore'>semaphore</span> <span class='op'>=</span> <span class='const'><span class='object_link'><a href="../Concurrent.html" title="Concurrent (module)">Concurrent</a></span></span><span class='op'>::</span><span class='const'>Semaphore</span><span class='period'>.</span><span class='id identifier rubyid_new'><span class='object_link'><a href="#initialize-instance_method" title="Concurrent::Semaphore#initialize (method)">new</a></span></span><span class='lparen'>(</span><span class='int'>2</span><span class='rparen'>)</span>
<span class='id identifier rubyid_t1'>t1</span> <span class='op'>=</span> <span class='const'>Thread</span><span class='period'>.</span><span class='id identifier rubyid_new'>new</span> <span class='kw'>do</span>
<span class='id identifier rubyid_semaphore'>semaphore</span><span class='period'>.</span><span class='id identifier rubyid_acquire'>acquire</span>
<span class='id identifier rubyid_puts'>puts</span> <span class='tstring'><span class='tstring_beg'>"</span><span class='tstring_content'>Thread 1 acquired semaphore</span><span class='tstring_end'>"</span></span>
<span class='kw'>end</span>
<span class='id identifier rubyid_t2'>t2</span> <span class='op'>=</span> <span class='const'>Thread</span><span class='period'>.</span><span class='id identifier rubyid_new'>new</span> <span class='kw'>do</span>
<span class='id identifier rubyid_semaphore'>semaphore</span><span class='period'>.</span><span class='id identifier rubyid_acquire'>acquire</span>
<span class='id identifier rubyid_puts'>puts</span> <span class='tstring'><span class='tstring_beg'>"</span><span class='tstring_content'>Thread 2 acquired semaphore</span><span class='tstring_end'>"</span></span>
<span class='kw'>end</span>
<span class='id identifier rubyid_t3'>t3</span> <span class='op'>=</span> <span class='const'>Thread</span><span class='period'>.</span><span class='id identifier rubyid_new'>new</span> <span class='kw'>do</span>
<span class='id identifier rubyid_semaphore'>semaphore</span><span class='period'>.</span><span class='id identifier rubyid_acquire'>acquire</span>
<span class='id identifier rubyid_puts'>puts</span> <span class='tstring'><span class='tstring_beg'>"</span><span class='tstring_content'>Thread 3 acquired semaphore</span><span class='tstring_end'>"</span></span>
<span class='kw'>end</span>
<span class='id identifier rubyid_t4'>t4</span> <span class='op'>=</span> <span class='const'>Thread</span><span class='period'>.</span><span class='id identifier rubyid_new'>new</span> <span class='kw'>do</span>
<span class='id identifier rubyid_sleep'>sleep</span><span class='lparen'>(</span><span class='int'>2</span><span class='rparen'>)</span>
<span class='id identifier rubyid_puts'>puts</span> <span class='tstring'><span class='tstring_beg'>"</span><span class='tstring_content'>Thread 4 releasing semaphore</span><span class='tstring_end'>"</span></span>
<span class='id identifier rubyid_semaphore'>semaphore</span><span class='period'>.</span><span class='id identifier rubyid_release'>release</span>
<span class='kw'>end</span>
<span class='lbracket'>[</span><span class='id identifier rubyid_t1'>t1</span><span class='comma'>,</span> <span class='id identifier rubyid_t2'>t2</span><span class='comma'>,</span> <span class='id identifier rubyid_t3'>t3</span><span class='comma'>,</span> <span class='id identifier rubyid_t4'>t4</span><span class='rbracket'>]</span><span class='period'>.</span><span class='id identifier rubyid_each'>each</span><span class='lparen'>(</span><span class='op'>&</span><span class='symbol'>:join</span><span class='rparen'>)</span>
<span class='comment'># prints:
</span><span class='comment'># Thread 3 acquired semaphore
</span><span class='comment'># Thread 2 acquired semaphore
</span><span class='comment'># Thread 4 releasing semaphore
</span><span class='comment'># Thread 1 acquired semaphore</span></code></pre>
</div>
</div>
<h2>
Instance Method Summary
<small><a href="#" class="summary_toggle">collapse</a></small>
</h2>
<ul class="summary">
<li class="public ">
<span class="summary_signature">
<a href="#acquire-instance_method" title="#acquire (instance method)">#<strong>acquire</strong>(permits = 1) ⇒ nil </a>
</span>
<span class="summary_desc"><div class='inline'><p>Acquires the given number of permits from this semaphore, blocking until all are available.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#available_permits-instance_method" title="#available_permits (instance method)">#<strong>available_permits</strong> ⇒ Integer </a>
</span>
<span class="summary_desc"><div class='inline'><p>Returns the current number of permits available in this semaphore.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#drain_permits-instance_method" title="#drain_permits (instance method)">#<strong>drain_permits</strong> ⇒ Integer </a>
</span>
<span class="summary_desc"><div class='inline'><p>Acquires and returns all permits that are immediately available.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#initialize-instance_method" title="#initialize (instance method)">#<strong>initialize</strong>(count) ⇒ undocumented </a>
</span>
<span class="note title constructor">constructor</span>
<span class="summary_desc"><div class='inline'><p>Create a new <code>Semaphore</code> with the initial <code>count</code>.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#release-instance_method" title="#release (instance method)">#<strong>release</strong>(permits = 1) ⇒ nil </a>
</span>
<span class="summary_desc"><div class='inline'><p>Releases the given number of permits, returning them to the semaphore.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#try_acquire-instance_method" title="#try_acquire (instance method)">#<strong>try_acquire</strong>(permits = 1, timeout = nil) ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Acquires the given number of permits from this semaphore, only if all are available at the time of invocation or within <code>timeout</code> interval.</p>
</div></span>
</li>
</ul>
<div id="constructor_details" class="method_details_list">
<h2>Constructor Details</h2>
<div class="method_details first">
<h3 class="signature first" id="initialize-instance_method">
#<strong>initialize</strong>(count) ⇒ <tt>undocumented</tt>
</h3><div class="docstring">
<div class="discussion">
<p>Create a new <code>Semaphore</code> with the initial <code>count</code>.</p>
</div>
</div>
<div class="tags">
<p class="tag_title">Parameters:</p>
<ul class="param">
<li>
<span class='name'>count</span>
<span class='type'>(<tt>Fixnum</tt>)</span>
—
<div class='inline'><p>the initial count</p>
</div>
</li>
</ul>
<p class="tag_title">Raises:</p>
<ul class="raise">
<li>
<span class='type'>(<tt>ArgumentError</tt>)</span>
—
<div class='inline'><p>if <code>count</code> is not an integer or is less than zero</p>
</div>
</li>
</ul>
</div><table class="source_code">
<tr>
<td>
<pre class="lines">
143
144</pre>
</td>
<td>
<pre class="code"><span class="info file"># File 'lib/concurrent/atomic/semaphore.rb', line 143</span>
<span class='kw'>class</span> <span class='const'><span class='object_link'><a href="" title="Concurrent::Semaphore (class)">Semaphore</a></span></span> <span class='op'><</span> <span class='const'>SemaphoreImplementation</span>
<span class='kw'>end</span></pre>
</td>
</tr>
</table>
</div>
</div>
<div id="instance_method_details" class="method_details_list">
<h2>Instance Method Details</h2>
<div class="method_details first">
<h3 class="signature first" id="acquire-instance_method">
#<strong>acquire</strong>(permits = 1) ⇒ <tt>nil</tt>
</h3><div class="docstring">
<div class="discussion">
<p>Acquires the given number of permits from this semaphore,
blocking until all are available.</p>
</div>
</div>
<div class="tags">
<p class="tag_title">Parameters:</p>
<ul class="param">
<li>
<span class='name'>permits</span>
<span class='type'>(<tt>Fixnum</tt>)</span>
<em class="default">(defaults to: <tt>1</tt>)</em>
—
<div class='inline'><p>Number of permits to acquire</p>
</div>
</li>
</ul>
<p class="tag_title">Returns:</p>
<ul class="return">
<li>
<span class='type'>(<tt>nil</tt>)</span>
</li>
</ul>
<p class="tag_title">Raises:</p>
<ul class="raise">
<li>
<span class='type'>(<tt>ArgumentError</tt>)</span>
—
<div class='inline'><p>if <code>permits</code> is not an integer or is less than
one</p>
</div>
</li>
</ul>
</div><table class="source_code">
<tr>
<td>
<pre class="lines">
143
144</pre>
</td>
<td>
<pre class="code"><span class="info file"># File 'lib/concurrent/atomic/semaphore.rb', line 143</span>
<span class='kw'>class</span> <span class='const'><span class='object_link'><a href="" title="Concurrent::Semaphore (class)">Semaphore</a></span></span> <span class='op'><</span> <span class='const'>SemaphoreImplementation</span>
<span class='kw'>end</span></pre>
</td>
</tr>
</table>
</div>
<div class="method_details ">
<h3 class="signature " id="available_permits-instance_method">
#<strong>available_permits</strong> ⇒ <tt>Integer</tt>
</h3><div class="docstring">
<div class="discussion">
<p>Returns the current number of permits available in this semaphore.</p>
</div>
</div>
<div class="tags">
<p class="tag_title">Returns:</p>
<ul class="return">
<li>
<span class='type'>(<tt>Integer</tt>)</span>
</li>
</ul>
</div><table class="source_code">
<tr>
<td>
<pre class="lines">
143
144</pre>
</td>
<td>
<pre class="code"><span class="info file"># File 'lib/concurrent/atomic/semaphore.rb', line 143</span>
<span class='kw'>class</span> <span class='const'><span class='object_link'><a href="" title="Concurrent::Semaphore (class)">Semaphore</a></span></span> <span class='op'><</span> <span class='const'>SemaphoreImplementation</span>
<span class='kw'>end</span></pre>
</td>
</tr>
</table>
</div>
<div class="method_details ">
<h3 class="signature " id="drain_permits-instance_method">
#<strong>drain_permits</strong> ⇒ <tt>Integer</tt>
</h3><div class="docstring">
<div class="discussion">
<p>Acquires and returns all permits that are immediately available.</p>
</div>
</div>
<div class="tags">
<p class="tag_title">Returns:</p>
<ul class="return">
<li>
<span class='type'>(<tt>Integer</tt>)</span>
</li>
</ul>
</div><table class="source_code">
<tr>
<td>
<pre class="lines">
143
144</pre>
</td>
<td>
<pre class="code"><span class="info file"># File 'lib/concurrent/atomic/semaphore.rb', line 143</span>
<span class='kw'>class</span> <span class='const'><span class='object_link'><a href="" title="Concurrent::Semaphore (class)">Semaphore</a></span></span> <span class='op'><</span> <span class='const'>SemaphoreImplementation</span>
<span class='kw'>end</span></pre>
</td>
</tr>
</table>
</div>
<div class="method_details ">
<h3 class="signature " id="release-instance_method">
#<strong>release</strong>(permits = 1) ⇒ <tt>nil</tt>
</h3><div class="docstring">
<div class="discussion">
<p>Releases the given number of permits, returning them to the semaphore.</p>
</div>
</div>
<div class="tags">
<p class="tag_title">Parameters:</p>
<ul class="param">
<li>
<span class='name'>permits</span>
<span class='type'>(<tt>Fixnum</tt>)</span>
<em class="default">(defaults to: <tt>1</tt>)</em>
—
<div class='inline'><p>Number of permits to return to the semaphore.</p>
</div>
</li>
</ul>
<p class="tag_title">Returns:</p>
<ul class="return">
<li>
<span class='type'>(<tt>nil</tt>)</span>
</li>
</ul>
<p class="tag_title">Raises:</p>
<ul class="raise">
<li>
<span class='type'>(<tt>ArgumentError</tt>)</span>
—
<div class='inline'><p>if <code>permits</code> is not a number or is less than one</p>
</div>
</li>
</ul>
</div><table class="source_code">
<tr>
<td>
<pre class="lines">
143
144</pre>
</td>
<td>
<pre class="code"><span class="info file"># File 'lib/concurrent/atomic/semaphore.rb', line 143</span>
<span class='kw'>class</span> <span class='const'><span class='object_link'><a href="" title="Concurrent::Semaphore (class)">Semaphore</a></span></span> <span class='op'><</span> <span class='const'>SemaphoreImplementation</span>
<span class='kw'>end</span></pre>
</td>
</tr>
</table>
</div>
<div class="method_details ">
<h3 class="signature " id="try_acquire-instance_method">
#<strong>try_acquire</strong>(permits = 1, timeout = nil) ⇒ <tt>Boolean</tt>
</h3><div class="docstring">
<div class="discussion">
<p>Acquires the given number of permits from this semaphore,
only if all are available at the time of invocation or within
<code>timeout</code> interval</p>
</div>
</div>
<div class="tags">
<p class="tag_title">Parameters:</p>
<ul class="param">
<li>
<span class='name'>permits</span>
<span class='type'>(<tt>Fixnum</tt>)</span>
<em class="default">(defaults to: <tt>1</tt>)</em>
—
<div class='inline'><p>the number of permits to acquire</p>
</div>
</li>
<li>
<span class='name'>timeout</span>
<span class='type'>(<tt>Fixnum</tt>)</span>
<em class="default">(defaults to: <tt>nil</tt>)</em>
—
<div class='inline'><p>the number of seconds to wait for the counter
or <code>nil</code> to return immediately</p>
</div>
</li>
</ul>
<p class="tag_title">Returns:</p>
<ul class="return">
<li>
<span class='type'>(<tt>Boolean</tt>)</span>
—
<div class='inline'><p><code>false</code> if no permits are available, <code>true</code> when
acquired a permit</p>
</div>
</li>
</ul>
<p class="tag_title">Raises:</p>
<ul class="raise">
<li>
<span class='type'>(<tt>ArgumentError</tt>)</span>
—
<div class='inline'><p>if <code>permits</code> is not an integer or is less than
one</p>
</div>
</li>
</ul>
</div><table class="source_code">
<tr>
<td>
<pre class="lines">
143
144</pre>
</td>
<td>
<pre class="code"><span class="info file"># File 'lib/concurrent/atomic/semaphore.rb', line 143</span>
<span class='kw'>class</span> <span class='const'><span class='object_link'><a href="" title="Concurrent::Semaphore (class)">Semaphore</a></span></span> <span class='op'><</span> <span class='const'>SemaphoreImplementation</span>
<span class='kw'>end</span></pre>
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