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Class: Concurrent::CachedThreadPool
— Concurrent Ruby
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<div id="content"><h1>Class: Concurrent::CachedThreadPool
</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::CachedThreadPool</li>
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<a href="#" class="inheritanceTree">show all</a>
</dd>
</dl>
<dl>
<dt>Defined in:</dt>
<dd>lib/concurrent-ruby/concurrent/executor/cached_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 dynamically grows and shrinks to fit the current workload.
New threads are created as needed, existing threads are reused, and threads
that remain idle for too long are killed and removed from the pool. These
pools are particularly suited to applications that perform a high volume of
short-lived tasks.</p>
<p>On creation a <code>CachedThreadPool</code> has zero running threads. New threads are
created on the pool as new operations are <code>#post</code>. The size of the pool
will grow until <code>#max_length</code> threads are in the pool or until the number
of threads exceeds the number of running and pending operations. When a new
operation is post to the pool the first available idle thread will be tasked
with the new operation.</p>
<p>Should a thread crash for any reason the thread will immediately be removed
from the pool. Similarly, threads which remain idle for an extended period
of time will be killed and reclaimed. Thus these thread pools are very
efficient at reclaiming unused resources.</p>
<p>The API and behavior of this class are based on Java's <code>CachedThreadPool</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>name</code>: The name of the executor (optional). Printed in the executor's <code>#to_s</code> output and
a <code><name>-worker-<id></code> name is given to its threads if supported by used Ruby
implementation. <code><id></code> is uniq for each thread.</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), the threads started will be marked as daemon.</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 threads can be marked as daemon according to the
<code>:auto_terminate</code> 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'><span class='object_link'><a href="FixedThreadPool.html" title="Concurrent::FixedThreadPool (class)">FixedThreadPool</a></span></span><span class='period'>.</span><span class='id identifier rubyid_new'><span class='object_link'><a href="FixedThreadPool.html#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'># threads will be marked as daemon
</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'><span class='object_link'><a href="FixedThreadPool.html" title="Concurrent::FixedThreadPool (class)">FixedThreadPool</a></span></span><span class='period'>.</span><span class='id identifier rubyid_new'><span class='object_link'><a href="FixedThreadPool.html#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'># mark threads as non-daemon
</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="https://docs.oracle.com/javase/8/docs/api/java/lang/Thread.html#setDaemon-boolean-" target="_parent" title="https://docs.oracle.com/javase/8/docs/api/java/lang/Thread.html#setDaemon-boolean-">https://docs.oracle.com/javase/8/docs/api/java/lang/Thread.html#setDaemon-boolean-</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>(opts = {}) ⇒ CachedThreadPool </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>(opts = {}) ⇒ <tt><span class='object_link'><a href="" title="Concurrent::CachedThreadPool (class)">CachedThreadPool</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'>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>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#newCachedThreadPool--" target="_parent" title="http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Executors.html#newCachedThreadPool--">http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Executors.html#newCachedThreadPool--</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-ruby/concurrent/executor/cached_thread_pool.rb', line 39</span>
<span class='kw'>def</span> <span class='id identifier rubyid_initialize'>initialize</span><span class='lparen'>(</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_defaults'>defaults</span> <span class='op'>=</span> <span class='lbrace'>{</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='int'>0</span><span class='comma'>,</span>
<span class='label'>max_threads:</span> <span class='const'>DEFAULT_MAX_POOL_SIZE</span><span class='comma'>,</span>
<span class='label'>max_queue:</span> <span class='const'>DEFAULT_MAX_QUEUE_SIZE</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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