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FixedThreadPool.html
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FixedThreadPool.html
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<!DOCTYPE html>
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Class: Concurrent::FixedThreadPool
— Concurrent Ruby
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<div id="content"><h1>Class: Concurrent::FixedThreadPool
</h1>
<div class="box_info">
<dl>
<dt>Inherits:</dt>
<dd>
<span class="inheritName"><span class='object_link'><a href="ThreadPoolExecutor.html" title="Concurrent::ThreadPoolExecutor (class)">ThreadPoolExecutor</a></span></span>
<ul class="fullTree">
<li>Object</li>
<li class="next"><span class='object_link'><a href="ThreadPoolExecutor.html" title="Concurrent::ThreadPoolExecutor (class)">ThreadPoolExecutor</a></span></li>
<li class="next">Concurrent::FixedThreadPool</li>
</ul>
<a href="#" class="inheritanceTree">show all</a>
</dd>
</dl>
<dl>
<dt>Defined in:</dt>
<dd>lib/concurrent/executor/fixed_thread_pool.rb</dd>
</dl>
</div>
<h2>Overview</h2><div class="docstring">
<div class="discussion">
<div class="note notetag">
<strong>Note:</strong>
<div class='inline'><p>Failure to properly shutdown a thread pool can lead to unpredictable results.
Please read <em>Shutting Down Thread Pools</em> for more information.</p>
</div>
</div>
<p>A thread pool that reuses a fixed number of threads operating off an unbounded queue.
At any point, at most <code>num_threads</code> will be active processing tasks. When all threads are busy new
tasks <code>#post</code> to the thread pool are enqueued until a thread becomes available.
Should a thread crash for any reason the thread will immediately be removed
from the pool and replaced.</p>
<p>The API and behavior of this class are based on Java's <code>FixedThreadPool</code></p>
<p><strong>Thread Pool Options</strong></p>
<p>Thread pools support several configuration options:</p>
<ul>
<li><code>idletime</code>: The number of seconds that a thread may be idle before being reclaimed.</li>
<li><code>max_queue</code>: The maximum number of tasks that may be waiting in the work queue at
any one time. When the queue size reaches <code>max_queue</code> and no new threads can be created,
subsequent tasks will be rejected in accordance with the configured <code>fallback_policy</code>.</li>
<li><code>auto_terminate</code>: When true (default) an <code>at_exit</code> handler will be registered which
will stop the thread pool when the application exits. See below for more information
on shutting down thread pools.</li>
<li><code>fallback_policy</code>: The policy defining how rejected tasks are handled.</li>
</ul>
<p>Three fallback policies are supported:</p>
<ul>
<li><code>:abort</code>: Raise a <code>RejectedExecutionError</code> exception and discard the task.</li>
<li><code>:discard</code>: Discard the task and return false.</li>
<li><code>:caller_runs</code>: Execute the task on the calling thread.</li>
</ul>
<p><strong>Shutting Down Thread Pools</strong></p>
<p>Killing a thread pool while tasks are still being processed, either by calling
the <code>#kill</code> method or at application exit, will have unpredictable results. There
is no way for the thread pool to know what resources are being used by the
in-progress tasks. When those tasks are killed the impact on those resources
cannot be predicted. The <em>best</em> practice is to explicitly shutdown all thread
pools using the provided methods:</p>
<ul>
<li>Call <code>#shutdown</code> to initiate an orderly termination of all in-progress tasks</li>
<li>Call <code>#wait_for_termination</code> with an appropriate timeout interval an allow
the orderly shutdown to complete</li>
<li>Call <code>#kill</code> <em>only when</em> the thread pool fails to shutdown in the allotted time</li>
</ul>
<p>On some runtime platforms (most notably the JVM) the application will not
exit until all thread pools have been shutdown. To prevent applications from
"hanging" on exit all thread pools include an <code>at_exit</code> handler that will
stop the thread pool when the application exits. This handler uses a brute
force method to stop the pool and makes no guarantees regarding resources being
used by any tasks still running. Registration of this <code>at_exit</code> handler can be
prevented by setting the thread pool's constructor <code>:auto_terminate</code> option to
<code>false</code> when the thread pool is created. All thread pools support this option.</p>
<pre class="code ruby"><code class="ruby"><span class='id identifier rubyid_pool1'>pool1</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'>FixedThreadPool</span><span class='period'>.</span><span class='id identifier rubyid_new'><span class='object_link'><a href="#initialize-instance_method" title="Concurrent::FixedThreadPool#initialize (method)">new</a></span></span><span class='lparen'>(</span><span class='int'>5</span><span class='rparen'>)</span> <span class='comment'># an `at_exit` handler will be registered
</span><span class='id identifier rubyid_pool2'>pool2</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'>FixedThreadPool</span><span class='period'>.</span><span class='id identifier rubyid_new'><span class='object_link'><a href="#initialize-instance_method" title="Concurrent::FixedThreadPool#initialize (method)">new</a></span></span><span class='lparen'>(</span><span class='int'>5</span><span class='comma'>,</span> <span class='label'>auto_terminate:</span> <span class='kw'>false</span><span class='rparen'>)</span> <span class='comment'># prevent `at_exit` handler registration
</span></code></pre>
</div>
</div>
<div class="tags">
<p class="tag_title">See Also:</p>
<ul class="see">
<li><a href="http://docs.oracle.com/javase/tutorial/essential/concurrency/pools.html" target="_parent" title="Java Tutorials: Thread Pools">Java Tutorials: Thread Pools</a></li>
<li><a href="http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Executors.html" target="_parent" title="Java Executors class">Java Executors class</a></li>
<li><a href="http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ExecutorService.html" target="_parent" title="Java ExecutorService interface">Java ExecutorService interface</a></li>
<li><a href="http://ruby-doc.org//core-2.2.0/Kernel.html#method-i-at_exit" target="_parent" title="Kernel#at_exit">Kernel#at_exit</a></li>
</ul>
</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="#initialize-instance_method" title="#initialize (instance method)">#<strong>initialize</strong>(num_threads, opts = {}) ⇒ FixedThreadPool </a>
</span>
<span class="note title constructor">constructor</span>
<span class="summary_desc"><div class='inline'><p>Create a new thread pool.</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>(num_threads, opts = {}) ⇒ <tt><span class='object_link'><a href="" title="Concurrent::FixedThreadPool (class)">FixedThreadPool</a></span></tt>
</h3><div class="docstring">
<div class="discussion">
<p>Create a new thread pool.</p>
</div>
</div>
<div class="tags">
<p class="tag_title">Parameters:</p>
<ul class="param">
<li>
<span class='name'>num_threads</span>
<span class='type'>(<tt>Integer</tt>)</span>
—
<div class='inline'><p>the number of threads to allocate</p>
</div>
</li>
<li>
<span class='name'>opts</span>
<span class='type'>(<tt><span class='object_link'><a href="Hash.html" title="Concurrent::Hash (class)">Hash</a></span></tt>)</span>
<em class="default">(defaults to: <tt>{}</tt>)</em>
—
<div class='inline'><p>the options defining pool behavior.</p>
</div>
</li>
</ul>
<p class="tag_title">Options Hash (<tt>opts</tt>):</p>
<ul class="option">
<li>
<span class="name">:fallback_policy</span>
<span class="type">(<tt>Symbol</tt>)</span>
<span class="default">
— default:
<tt>`:abort`</tt>
</span>
— <div class='inline'><p>the fallback policy</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>num_threads</code> is less than or equal to zero</p>
</div>
</li>
<li>
<span class='type'>(<tt>ArgumentError</tt>)</span>
—
<div class='inline'><p>if <code>fallback_policy</code> is not a known policy</p>
</div>
</li>
</ul>
<p class="tag_title">See Also:</p>
<ul class="see">
<li><a href="http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Executors.html#newFixedThreadPool-int-" target="_parent" title="http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Executors.html#newFixedThreadPool-int-">http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Executors.html#newFixedThreadPool-int-</a></li>
</ul>
</div><table class="source_code">
<tr>
<td>
<pre class="lines">
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</td>
<td>
<pre class="code"><span class="info file"># File 'lib/concurrent/executor/fixed_thread_pool.rb', line 197</span>
<span class='kw'>def</span> <span class='id identifier rubyid_initialize'>initialize</span><span class='lparen'>(</span><span class='id identifier rubyid_num_threads'>num_threads</span><span class='comma'>,</span> <span class='id identifier rubyid_opts'>opts</span> <span class='op'>=</span> <span class='lbrace'>{</span><span class='rbrace'>}</span><span class='rparen'>)</span>
<span class='id identifier rubyid_raise'>raise</span> <span class='const'>ArgumentError</span><span class='period'>.</span><span class='id identifier rubyid_new'>new</span><span class='lparen'>(</span><span class='tstring'><span class='tstring_beg'>'</span><span class='tstring_content'>number of threads must be greater than zero</span><span class='tstring_end'>'</span></span><span class='rparen'>)</span> <span class='kw'>if</span> <span class='id identifier rubyid_num_threads'>num_threads</span><span class='period'>.</span><span class='id identifier rubyid_to_i'>to_i</span> <span class='op'><</span> <span class='int'>1</span>
<span class='id identifier rubyid_defaults'>defaults</span> <span class='op'>=</span> <span class='lbrace'>{</span> <span class='label'>max_queue:</span> <span class='const'>DEFAULT_MAX_QUEUE_SIZE</span><span class='comma'>,</span>
<span class='label'>idletime:</span> <span class='const'>DEFAULT_THREAD_IDLETIMEOUT</span> <span class='rbrace'>}</span>
<span class='id identifier rubyid_overrides'>overrides</span> <span class='op'>=</span> <span class='lbrace'>{</span> <span class='label'>min_threads:</span> <span class='id identifier rubyid_num_threads'>num_threads</span><span class='comma'>,</span>
<span class='label'>max_threads:</span> <span class='id identifier rubyid_num_threads'>num_threads</span> <span class='rbrace'>}</span>
<span class='kw'>super</span><span class='lparen'>(</span><span class='id identifier rubyid_defaults'>defaults</span><span class='period'>.</span><span class='id identifier rubyid_merge'>merge</span><span class='lparen'>(</span><span class='id identifier rubyid_opts'>opts</span><span class='rparen'>)</span><span class='period'>.</span><span class='id identifier rubyid_merge'>merge</span><span class='lparen'>(</span><span class='id identifier rubyid_overrides'>overrides</span><span class='rparen'>)</span><span class='rparen'>)</span>
<span class='kw'>end</span></pre>
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