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ThreadPoolExecutor.html
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ThreadPoolExecutor.html
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<!DOCTYPE html>
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Class: Concurrent::ThreadPoolExecutor
— Concurrent Ruby
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<div id="content"><h1>Class: Concurrent::ThreadPoolExecutor
</h1>
<div class="box_info">
<dl>
<dt>Inherits:</dt>
<dd>
<span class="inheritName"><span class='object_link'>ThreadPoolExecutorImplementation</span></span>
<ul class="fullTree">
<li>Object</li>
<li class="next">Concurrent::ThreadPoolExecutor</li>
</ul>
<a href="#" class="inheritanceTree">show all</a>
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<dl>
<dt>Defined in:</dt>
<dd>lib/concurrent/executor/thread_pool_executor.rb</dd>
</dl>
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<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>An abstraction composed of one or more threads and a task queue. Tasks
(blocks or <code>proc</code> objects) are submitted to the pool and added to the queue.
The threads in the pool remove the tasks and execute them in the order
they were received.</p>
<p>A <code>ThreadPoolExecutor</code> will automatically adjust the pool size according
to the bounds set by <code>min-threads</code> and <code>max-threads</code>. When a new task is
submitted and fewer than <code>min-threads</code> threads are running, a new thread
is created to handle the request, even if other worker threads are idle.
If there are more than <code>min-threads</code> but less than <code>max-threads</code> threads
running, a new thread will be created only if the queue is full.</p>
<p>Threads that are idle for too long will be garbage collected, down to the
configured minimum options. Should a thread crash it, too, will be garbage collected.</p>
<p><code>ThreadPoolExecutor</code> is based on the Java class of the same name. From
the official Java documentation;</p>
<blockquote>
<p>Thread pools address two different problems: they usually provide
improved performance when executing large numbers of asynchronous tasks,
due to reduced per-task invocation overhead, and they provide a means
of bounding and managing the resources, including threads, consumed
when executing a collection of tasks. Each ThreadPoolExecutor also
maintains some basic statistics, such as the number of completed tasks.</p>
<p>To be useful across a wide range of contexts, this class provides many
adjustable parameters and extensibility hooks. However, programmers are
urged to use the more convenient Executors factory methods
<a href="unbounded%20thread%20pool,%20with%20automatic%20thread%20reclamation">CachedThreadPool</a>,
<a href="fixed%20size%20thread%20pool">FixedThreadPool</a> and <a href="single%0Abackground%20thread">SingleThreadExecutor</a>, that preconfigure settings for the most common usage
scenarios.</p>
</blockquote>
<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'><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'># 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'><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'># 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><div id="subclasses">
<h2>Direct Known Subclasses</h2>
<p class="children"><span class='object_link'><a href="CachedThreadPool.html" title="Concurrent::CachedThreadPool (class)">CachedThreadPool</a></span>, <span class='object_link'><a href="FixedThreadPool.html" title="Concurrent::FixedThreadPool (class)">FixedThreadPool</a></span></p>
</div>
<h2>Instance Attribute Summary <small><a href="#" class="summary_toggle">collapse</a></small></h2>
<ul class="summary">
<li class="public ">
<span class="summary_signature">
<a href="#completed_task_count-instance_method" title="#completed_task_count (instance method)">#<strong>completed_task_count</strong> ⇒ Integer </a>
</span>
<span class="note title readonly">readonly</span>
<span class="summary_desc"><div class='inline'><p>The number of tasks that have been completed by the pool since construction.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#fallback_policy-instance_method" title="#fallback_policy (instance method)">#<strong>fallback_policy</strong> ⇒ Symbol </a>
</span>
<span class="note title readonly">readonly</span>
<span class="summary_desc"><div class='inline'><p>The fallback policy in effect.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#idletime-instance_method" title="#idletime (instance method)">#<strong>idletime</strong> ⇒ Integer </a>
</span>
<span class="note title readonly">readonly</span>
<span class="summary_desc"><div class='inline'><p>The number of seconds that a thread may be idle before being reclaimed.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#largest_length-instance_method" title="#largest_length (instance method)">#<strong>largest_length</strong> ⇒ Integer </a>
</span>
<span class="note title readonly">readonly</span>
<span class="summary_desc"><div class='inline'><p>The largest number of threads that have been created in the pool since construction.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#length-instance_method" title="#length (instance method)">#<strong>length</strong> ⇒ Integer </a>
</span>
<span class="note title readonly">readonly</span>
<span class="summary_desc"><div class='inline'><p>The number of threads currently in the pool.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#max_length-instance_method" title="#max_length (instance method)">#<strong>max_length</strong> ⇒ Integer </a>
</span>
<span class="note title readonly">readonly</span>
<span class="summary_desc"><div class='inline'><p>The maximum number of threads that may be created in the pool.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#max_queue-instance_method" title="#max_queue (instance method)">#<strong>max_queue</strong> ⇒ Integer </a>
</span>
<span class="note title readonly">readonly</span>
<span class="summary_desc"><div class='inline'><p>The maximum number of tasks that may be waiting in the work queue at any one time.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#min_length-instance_method" title="#min_length (instance method)">#<strong>min_length</strong> ⇒ Integer </a>
</span>
<span class="note title readonly">readonly</span>
<span class="summary_desc"><div class='inline'><p>The minimum number of threads that may be retained in the pool.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#queue_length-instance_method" title="#queue_length (instance method)">#<strong>queue_length</strong> ⇒ Integer </a>
</span>
<span class="note title readonly">readonly</span>
<span class="summary_desc"><div class='inline'><p>The number of tasks in the queue awaiting execution.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#remaining_capacity-instance_method" title="#remaining_capacity (instance method)">#<strong>remaining_capacity</strong> ⇒ Integer </a>
</span>
<span class="note title readonly">readonly</span>
<span class="summary_desc"><div class='inline'><p>Number of tasks that may be enqueued before reaching <code>max_queue</code> and rejecting new tasks.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#scheduled_task_count-instance_method" title="#scheduled_task_count (instance method)">#<strong>scheduled_task_count</strong> ⇒ Integer </a>
</span>
<span class="note title readonly">readonly</span>
<span class="summary_desc"><div class='inline'><p>The number of tasks that have been scheduled for execution on the pool since construction.</p>
</div></span>
</li>
</ul>
<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="#<<-instance_method" title="#<< (instance method)">#<strong><<</strong>(task) ⇒ self </a>
</span>
<span class="summary_desc"><div class='inline'><p>Submit a task to the executor for asynchronous processing.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#auto_terminate=-instance_method" title="#auto_terminate= (instance method)">#<strong>auto_terminate=</strong>(value) ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Set the auto-terminate behavior for this executor.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#auto_terminate%3F-instance_method" title="#auto_terminate? (instance method)">#<strong>auto_terminate?</strong> ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Is the executor auto-terminate when the application exits?.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#can_overflow%3F-instance_method" title="#can_overflow? (instance method)">#<strong>can_overflow?</strong> ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Does the task queue have a maximum size?.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#initialize-instance_method" title="#initialize (instance method)">#<strong>initialize</strong>(opts = {}) ⇒ undocumented </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>
<li class="public ">
<span class="summary_signature">
<a href="#kill-instance_method" title="#kill (instance method)">#<strong>kill</strong> ⇒ undocumented </a>
</span>
<span class="summary_desc"><div class='inline'><p>Begin an immediate shutdown.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#post-instance_method" title="#post (instance method)">#<strong>post</strong>(*args) { ... } ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Submit a task to the executor for asynchronous processing.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#running%3F-instance_method" title="#running? (instance method)">#<strong>running?</strong> ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Is the executor running?.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#serialized%3F-instance_method" title="#serialized? (instance method)">#<strong>serialized?</strong> ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Does this executor guarantee serialization of its operations?.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#shutdown-instance_method" title="#shutdown (instance method)">#<strong>shutdown</strong> ⇒ undocumented </a>
</span>
<span class="summary_desc"><div class='inline'><p>Begin an orderly shutdown.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#shutdown%3F-instance_method" title="#shutdown? (instance method)">#<strong>shutdown?</strong> ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Is the executor shutdown?.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#shuttingdown%3F-instance_method" title="#shuttingdown? (instance method)">#<strong>shuttingdown?</strong> ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Is the executor shuttingdown?.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#wait_for_termination-instance_method" title="#wait_for_termination (instance method)">#<strong>wait_for_termination</strong>(timeout = nil) ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Block until executor shutdown is complete or until <code>timeout</code> seconds have passed.</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>undocumented</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 which configure the thread pool.</p>
</div>
</li>
</ul>
<p class="tag_title">Options Hash (<tt>opts</tt>):</p>
<ul class="option">
<li>
<span class="name">:max_threads</span>
<span class="type">(<tt>Integer</tt>)</span>
<span class="default">
— default:
<tt>DEFAULT_MAX_POOL_SIZE</tt>
</span>
— <div class='inline'><p>the maximum
number of threads to be created</p>
</div>
</li>
<li>
<span class="name">:min_threads</span>
<span class="type">(<tt>Integer</tt>)</span>
<span class="default">
— default:
<tt>DEFAULT_MIN_POOL_SIZE</tt>
</span>
— <div class='inline'><p>When a new task is submitted
and fewer than <code>min_threads</code> are running, a new thread is created</p>
</div>
</li>
<li>
<span class="name">:idletime</span>
<span class="type">(<tt>Integer</tt>)</span>
<span class="default">
— default:
<tt>DEFAULT_THREAD_IDLETIMEOUT</tt>
</span>
— <div class='inline'><p>the maximum
number of seconds a thread may be idle before being reclaimed</p>
</div>
</li>
<li>
<span class="name">:max_queue</span>
<span class="type">(<tt>Integer</tt>)</span>
<span class="default">
— default:
<tt>DEFAULT_MAX_QUEUE_SIZE</tt>
</span>
— <div class='inline'><p>the maximum
number of tasks allowed in the work queue at any one time; a value of
zero means the queue may grow without bound</p>
</div>
</li>
<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 policy for handling new
tasks that are received when the queue size has reached
<code>max_queue</code> or the executor has shut down</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>:max_threads</code> is less than one</p>
</div>
</li>