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Class: Concurrent::Future
— Concurrent Ruby
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<div id="content"><h1>Class: Concurrent::Future
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<span class="inheritName"><span class='object_link'><a href="IVar.html" title="Concurrent::IVar (class)">IVar</a></span></span>
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<li>Object</li>
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<h2>Overview</h2><div class="docstring">
<div class="discussion">
<p><code>Future</code> is inspired by <a href="http://clojure.org/">Clojure's</a> <a href="http://clojuredocs.org/clojure_core/clojure.core/future">future</a> function. A future represents a promise to complete an action at some time in the future. The action is atomic and permanent. The idea behind a future is to send an operation for asynchronous completion, do other stuff, then return and retrieve the result of the async operation at a later time. <code>Future</code>s run on the global thread pool.</p>
<pre class="code cucumber"><code class="cucumber">Feature:
As a highly responsive Ruby application
I want long-running tasks on a separate thread
So I can perform other tasks without waiting
</code></pre>
<p><code>Future</code>s have several possible states: <em>:unscheduled</em>, <em>:pending</em>, <em>:processing</em>, <em>:rejected</em>, or <em>:fulfilled</em>. These are also aggregated as <code>#incomplete?</code> and <code>#complete?</code>. When a <code>Future</code> is created it is set to <em>:unscheduled</em>. Once the <code>#execute</code> method is called the state becomes <em>:pending</em>. Once a job is pulled from the thread pool's queue and is given to a thread for processing (often immediately upon <code>#post</code>) the state becomes <em>:processing</em>. The future will remain in this state until processing is complete. A future that is in the <em>:unscheduled</em>, <em>:pending</em>, or <em>:processing</em> is considered <code>#incomplete?</code>. A <code>#complete?</code> <code>Future</code> is either <em>:rejected</em>, indicating that an exception was thrown during processing, or <em>:fulfilled</em>, indicating success. If a <code>Future</code> is <em>:fulfilled</em> its <code>#value</code> will be updated to reflect the result of the operation. If <em>:rejected</em> the <code>reason</code> will be updated with a reference to the thrown exception. The predicate methods <code>#unscheduled?</code>, <code>#pending?</code>, <code>#rejected?</code>, and <code>#fulfilled?</code> can be called at any time to obtain the state of the <code>Future</code>, as can the <code>#state</code> method, which returns a symbol.</p>
<p>Retrieving the value of a <code>Future</code> is done through the <code>#value</code> (alias: <code>#deref</code>) method. Obtaining the value of a <code>Future</code> is a potentially blocking operation. When a <code>Future</code> is <em>:rejected</em> a call to <code>#value</code> will return <code>nil</code> immediately. When a <code>Future</code> is <em>:fulfilled</em> a call to <code>#value</code> will immediately return the current value. When a <code>Future</code> is <em>:pending</em> a call to <code>#value</code> will block until the <code>Future</code> is either <em>:rejected</em> or <em>:fulfilled</em>. A <em>timeout</em> value can be passed to <code>#value</code> to limit how long the call will block. If <code>nil</code> the call will block indefinitely. If <code>0</code> the call will not block. Any other integer or float value will indicate the maximum number of seconds to block.</p>
<p>The constructor can also be given zero or more processing options. Currently the only supported options are those recognized by the <a href="Dereferenceable">Dereferenceable</a> module.</p>
<p>The <code>Future</code> class also includes the behavior of the Ruby standard library <a href="http://ruby-doc.org/stdlib-2.0/libdoc/observer/rdoc/Observable.html">Observable</a> module, but does so in a thread-safe way. On fulfillment or rejection all observers will be notified according to the normal <code>Observable</code> behavior. The observer callback function will be called with three parameters: the <code>Time</code> of fulfillment/rejection, the final <code>value</code>, and the final <code>reason</code>. Observers added after fulfillment/rejection will still be notified as normal. The notification will occur on the same thread that processed the job.</p>
<h3>Examples</h3>
<p>A fulfilled example:</p>
<pre class="code ruby"><code class="ruby"><span class='id identifier rubyid_require'>require</span> <span class='tstring'><span class='tstring_beg'>'</span><span class='tstring_content'>concurrent</span><span class='tstring_end'>'</span></span>
<span class='id identifier rubyid_require'>require</span> <span class='tstring'><span class='tstring_beg'>'</span><span class='tstring_content'>thread</span><span class='tstring_end'>'</span></span> <span class='comment'># for Queue
</span><span class='id identifier rubyid_require'>require</span> <span class='tstring'><span class='tstring_beg'>'</span><span class='tstring_content'>open-uri</span><span class='tstring_end'>'</span></span> <span class='comment'># for open(uri)
</span>
<span class='kw'>class</span> <span class='const'>Ticker</span>
<span class='kw'>def</span> <span class='id identifier rubyid_get_year_end_closing'>get_year_end_closing</span><span class='lparen'>(</span><span class='id identifier rubyid_symbol'>symbol</span><span class='comma'>,</span> <span class='id identifier rubyid_year'>year</span><span class='rparen'>)</span>
<span class='id identifier rubyid_uri'>uri</span> <span class='op'>=</span> <span class='tstring'><span class='tstring_beg'>"</span><span class='tstring_content'>http://ichart.finance.yahoo.com/table.csv?s=</span><span class='embexpr_beg'>#{</span><span class='id identifier rubyid_symbol'>symbol</span><span class='embexpr_end'>}</span><span class='tstring_content'>&a=11&b=01&c=</span><span class='embexpr_beg'>#{</span><span class='id identifier rubyid_year'>year</span><span class='embexpr_end'>}</span><span class='tstring_content'>&d=11&e=31&f=</span><span class='embexpr_beg'>#{</span><span class='id identifier rubyid_year'>year</span><span class='embexpr_end'>}</span><span class='tstring_content'>&g=m</span><span class='tstring_end'>"</span></span>
<span class='id identifier rubyid_data'>data</span> <span class='op'>=</span> <span class='id identifier rubyid_open'>open</span><span class='lparen'>(</span><span class='id identifier rubyid_uri'>uri</span><span class='rparen'>)</span> <span class='lbrace'>{</span><span class='op'>|</span><span class='id identifier rubyid_f'>f</span><span class='op'>|</span> <span class='id identifier rubyid_f'>f</span><span class='period'>.</span><span class='id identifier rubyid_collect'>collect</span><span class='lbrace'>{</span><span class='op'>|</span><span class='id identifier rubyid_line'>line</span><span class='op'>|</span> <span class='id identifier rubyid_line'>line</span><span class='period'>.</span><span class='id identifier rubyid_strip'>strip</span> <span class='rbrace'>}</span> <span class='rbrace'>}</span>
<span class='id identifier rubyid_data'>data</span><span class='lbracket'>[</span><span class='int'>1</span><span class='rbracket'>]</span><span class='period'>.</span><span class='id identifier rubyid_split'>split</span><span class='lparen'>(</span><span class='tstring'><span class='tstring_beg'>'</span><span class='tstring_content'>,</span><span class='tstring_end'>'</span></span><span class='rparen'>)</span><span class='lbracket'>[</span><span class='int'>4</span><span class='rbracket'>]</span><span class='period'>.</span><span class='id identifier rubyid_to_f'>to_f</span>
<span class='kw'>end</span>
<span class='kw'>end</span>
<span class='comment'># Future
</span><span class='id identifier rubyid_price'>price</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'>Future</span><span class='period'>.</span><span class='id identifier rubyid_execute'><span class='object_link'><a href="#execute-class_method" title="Concurrent::Future.execute (method)">execute</a></span></span><span class='lbrace'>{</span> <span class='const'>Ticker</span><span class='period'>.</span><span class='id identifier rubyid_new'>new</span><span class='period'>.</span><span class='id identifier rubyid_get_year_end_closing'>get_year_end_closing</span><span class='lparen'>(</span><span class='tstring'><span class='tstring_beg'>'</span><span class='tstring_content'>TWTR</span><span class='tstring_end'>'</span></span><span class='comma'>,</span> <span class='int'>2013</span><span class='rparen'>)</span> <span class='rbrace'>}</span>
<span class='id identifier rubyid_price'>price</span><span class='period'>.</span><span class='id identifier rubyid_state'>state</span> <span class='comment'>#=> :pending
</span><span class='id identifier rubyid_price'>price</span><span class='period'>.</span><span class='id identifier rubyid_pending?'>pending?</span> <span class='comment'>#=> true
</span><span class='id identifier rubyid_price'>price</span><span class='period'>.</span><span class='id identifier rubyid_value'>value</span><span class='lparen'>(</span><span class='int'>0</span><span class='rparen'>)</span> <span class='comment'>#=> nil (does not block)
</span>
<span class='id identifier rubyid_sleep'>sleep</span><span class='lparen'>(</span><span class='int'>1</span><span class='rparen'>)</span> <span class='comment'># do other stuff
</span>
<span class='id identifier rubyid_price'>price</span><span class='period'>.</span><span class='id identifier rubyid_value'>value</span> <span class='comment'>#=> 63.65 (after blocking if necessary)
</span><span class='id identifier rubyid_price'>price</span><span class='period'>.</span><span class='id identifier rubyid_state'>state</span> <span class='comment'>#=> :fulfilled
</span><span class='id identifier rubyid_price'>price</span><span class='period'>.</span><span class='id identifier rubyid_fulfilled?'>fulfilled?</span> <span class='comment'>#=> true
</span><span class='id identifier rubyid_price'>price</span><span class='period'>.</span><span class='id identifier rubyid_value'>value</span> <span class='comment'>#=> 63.65
</span></code></pre>
<p>A rejected example:</p>
<pre class="code ruby"><code class="ruby"><span class='id identifier rubyid_count'>count</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'>Future</span><span class='period'>.</span><span class='id identifier rubyid_execute'><span class='object_link'><a href="#execute-class_method" title="Concurrent::Future.execute (method)">execute</a></span></span><span class='lbrace'>{</span> <span class='id identifier rubyid_sleep'>sleep</span><span class='lparen'>(</span><span class='int'>10</span><span class='rparen'>)</span><span class='semicolon'>;</span> <span class='id identifier rubyid_raise'>raise</span> <span class='const'>StandardError</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'>Boom!</span><span class='tstring_end'>"</span></span><span class='rparen'>)</span> <span class='rbrace'>}</span>
<span class='id identifier rubyid_count'>count</span><span class='period'>.</span><span class='id identifier rubyid_state'>state</span> <span class='comment'>#=> :pending
</span><span class='id identifier rubyid_count'>count</span><span class='period'>.</span><span class='id identifier rubyid_pending?'>pending?</span> <span class='comment'>#=> true
</span>
<span class='id identifier rubyid_count'>count</span><span class='period'>.</span><span class='id identifier rubyid_value'>value</span> <span class='comment'>#=> nil (after blocking)
</span><span class='id identifier rubyid_count'>count</span><span class='period'>.</span><span class='id identifier rubyid_rejected?'>rejected?</span> <span class='comment'>#=> true
</span><span class='id identifier rubyid_count'>count</span><span class='period'>.</span><span class='id identifier rubyid_reason'>reason</span> <span class='comment'>#=> #<StandardError: Boom!>
</span></code></pre>
<p>An example with observation:</p>
<pre class="code ruby"><code class="ruby"><span class='kw'>class</span> <span class='const'>Ticker</span>
<span class='const'>Stock</span> <span class='op'>=</span> <span class='const'>Struct</span><span class='period'>.</span><span class='id identifier rubyid_new'>new</span><span class='lparen'>(</span><span class='symbol'>:symbol</span><span class='comma'>,</span> <span class='symbol'>:name</span><span class='comma'>,</span> <span class='symbol'>:exchange</span><span class='rparen'>)</span>
<span class='kw'>def</span> <span class='id identifier rubyid_update'>update</span><span class='lparen'>(</span><span class='id identifier rubyid_time'>time</span><span class='comma'>,</span> <span class='id identifier rubyid_value'>value</span><span class='comma'>,</span> <span class='id identifier rubyid_reason'>reason</span><span class='rparen'>)</span>
<span class='id identifier rubyid_ticker'>ticker</span> <span class='op'>=</span> <span class='id identifier rubyid_value'>value</span><span class='period'>.</span><span class='id identifier rubyid_collect'>collect</span> <span class='kw'>do</span> <span class='op'>|</span><span class='id identifier rubyid_symbol'>symbol</span><span class='op'>|</span>
<span class='const'>Stock</span><span class='period'>.</span><span class='id identifier rubyid_new'>new</span><span class='lparen'>(</span><span class='id identifier rubyid_symbol'>symbol</span><span class='lbracket'>[</span><span class='tstring'><span class='tstring_beg'>'</span><span class='tstring_content'>symbol</span><span class='tstring_end'>'</span></span><span class='rbracket'>]</span><span class='comma'>,</span> <span class='id identifier rubyid_symbol'>symbol</span><span class='lbracket'>[</span><span class='tstring'><span class='tstring_beg'>'</span><span class='tstring_content'>name</span><span class='tstring_end'>'</span></span><span class='rbracket'>]</span><span class='comma'>,</span> <span class='id identifier rubyid_symbol'>symbol</span><span class='lbracket'>[</span><span class='tstring'><span class='tstring_beg'>'</span><span class='tstring_content'>exch</span><span class='tstring_end'>'</span></span><span class='rbracket'>]</span><span class='rparen'>)</span>
<span class='kw'>end</span>
<span class='id identifier rubyid_output'>output</span> <span class='op'>=</span> <span class='id identifier rubyid_ticker'>ticker</span><span class='period'>.</span><span class='id identifier rubyid_join'>join</span><span class='lparen'>(</span><span class='tstring'><span class='tstring_beg'>"</span><span class='tstring_content'>\n</span><span class='tstring_end'>"</span></span><span class='rparen'>)</span>
<span class='id identifier rubyid_print'>print</span> <span class='tstring'><span class='tstring_beg'>"</span><span class='embexpr_beg'>#{</span><span class='id identifier rubyid_output'>output</span><span class='embexpr_end'>}</span><span class='tstring_content'>\n</span><span class='tstring_end'>"</span></span>
<span class='kw'>end</span>
<span class='kw'>end</span>
<span class='id identifier rubyid_yahoo'>yahoo</span> <span class='op'>=</span> <span class='const'>Finance</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'>YAHOO</span><span class='tstring_end'>'</span></span><span class='rparen'>)</span>
<span class='id identifier rubyid_future'>future</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'>Future</span><span class='period'>.</span><span class='id identifier rubyid_new'><span class='object_link'><a href="#initialize-instance_method" title="Concurrent::Future#initialize (method)">new</a></span></span> <span class='lbrace'>{</span> <span class='id identifier rubyid_yahoo'>yahoo</span><span class='period'>.</span><span class='id identifier rubyid_update'>update</span><span class='period'>.</span><span class='id identifier rubyid_suggested_symbols'>suggested_symbols</span> <span class='rbrace'>}</span>
<span class='id identifier rubyid_future'>future</span><span class='period'>.</span><span class='id identifier rubyid_add_observer'>add_observer</span><span class='lparen'>(</span><span class='const'>Ticker</span><span class='period'>.</span><span class='id identifier rubyid_new'>new</span><span class='rparen'>)</span>
<span class='id identifier rubyid_future'>future</span><span class='period'>.</span><span class='id identifier rubyid_execute'>execute</span>
<span class='comment'># do important stuff...
</span>
<span class='comment'>#>> #<struct Ticker::Stock symbol="YHOO", name="Yahoo! Inc.", exchange="NMS">
</span><span class='comment'>#>> #<struct Ticker::Stock symbol="YHO.DE", name="Yahoo! Inc.", exchange="GER">
</span><span class='comment'>#>> #<struct Ticker::Stock symbol="YAHOY", name="Yahoo Japan Corporation", exchange="PNK">
</span><span class='comment'>#>> #<struct Ticker::Stock symbol="YAHOF", name="YAHOO JAPAN CORP", exchange="PNK">
</span><span class='comment'>#>> #<struct Ticker::Stock symbol="YOJ.SG", name="YAHOO JAPAN", exchange="STU">
</span><span class='comment'>#>> #<struct Ticker::Stock symbol="YHO.SG", name="YAHOO", exchange="STU">
</span><span class='comment'>#>> #<struct Ticker::Stock symbol="YHOO.BA", name="Yahoo! Inc.", exchange="BUE">
</span><span class='comment'>#>> #<struct Ticker::Stock symbol="YHO.DU", name="YAHOO", exchange="DUS">
</span><span class='comment'>#>> #<struct Ticker::Stock symbol="YHO.HM", name="YAHOO", exchange="HAM">
</span><span class='comment'>#>> #<struct Ticker::Stock symbol="YHO.BE", name="YAHOO", exchange="BER">
</span></code></pre>
</p>
<h2>Copy Options</h2>
<p>Object references in Ruby are mutable. This can lead to serious
problems when the <span class='object_link'><a href="Concern/Obligation.html#value-instance_method" title="Concurrent::Concern::Obligation#value (method)">Concern::Obligation#value</a></span> of an object is a mutable reference. Which
is always the case unless the value is a <code>Fixnum</code>, <code>Symbol</code>, or similar
"primitive" data type. Each instance can be configured with a few
options that can help protect the program from potentially dangerous
operations. Each of these options can be optionally set when the object
instance is created:</p>
<ul>
<li><code>:dup_on_deref</code> When true the object will call the <code>#dup</code> method on
the <code>value</code> object every time the <code>#value</code> method is called
(default: false)</li>
<li><code>:freeze_on_deref</code> When true the object will call the <code>#freeze</code>
method on the <code>value</code> object every time the <code>#value</code> method is called
(default: false)</li>
<li><code>:copy_on_deref</code> When given a <code>Proc</code> object the <code>Proc</code> will be run
every time the <code>#value</code> method is called. The <code>Proc</code> will be given
the current <code>value</code> as its only argument and the result returned by
the block will be the return value of the <code>#value</code> call. When <code>nil</code>
this option will be ignored (default: nil)</li>
</ul>
<p>When multiple deref options are set the order of operations is strictly defined.
The order of deref operations is:</p>
<ul>
<li><code>:copy_on_deref</code></li>
<li><code>:dup_on_deref</code></li>
<li><code>:freeze_on_deref</code></li>
</ul>
<p>Because of this ordering there is no need to <code>#freeze</code> an object created by a
provided <code>:copy_on_deref</code> block. Simply set <code>:freeze_on_deref</code> to <code>true</code>.
Setting both <code>:dup_on_deref</code> to <code>true</code> and <code>:freeze_on_deref</code> to <code>true</code> is
as close to the behavior of a "pure" functional language (like Erlang, Clojure,
or Haskell) as we are likely to get in Ruby.</p>
</div>
</div>
<div class="tags">
<p class="tag_title">See Also:</p>
<ul class="see">
<li><a href="http://ruby-doc.org/stdlib-2.1.1/libdoc/observer/rdoc/Observable.html" target="_parent" title="Ruby Observable module">Ruby Observable module</a></li>
<li><a href="http://clojuredocs.org/clojure_core/clojure.core/future" target="_parent" title="Clojure's future function">Clojure's future function</a></li>
<li><a href="http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Future.html" target="_parent" title="java.util.concurrent.Future">java.util.concurrent.Future</a></li>
</ul>
</div>
<h2>
Class Method Summary
<small><a href="#" class="summary_toggle">collapse</a></small>
</h2>
<ul class="summary">
<li class="public ">
<span class="summary_signature">
<a href="#execute-class_method" title="execute (class method)">.<strong>execute</strong>(opts = {}) { ... } ⇒ Future </a>
</span>
<span class="summary_desc"><div class='inline'><p>Create a new <code>Future</code> object with the given block, execute it, and return the <code>:pending</code> object.</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="#cancel-instance_method" title="#cancel (instance method)">#<strong>cancel</strong> ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Attempt to cancel the operation if it has not already processed.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#cancelled%3F-instance_method" title="#cancelled? (instance method)">#<strong>cancelled?</strong> ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Has the operation been successfully cancelled?.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#execute-instance_method" title="#execute (instance method)">#<strong>execute</strong> ⇒ Future </a>
</span>
<span class="summary_desc"><div class='inline'><p>Execute an <code>:unscheduled</code> <code>Future</code>.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#initialize-instance_method" title="#initialize (instance method)">#<strong>initialize</strong>(opts = {}) { ... } ⇒ Future </a>
</span>
<span class="note title constructor">constructor</span>
<span class="summary_desc"><div class='inline'><p>Create a new <code>Future</code> in the <code>:unscheduled</code> state.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#set-instance_method" title="#set (instance method)">#<strong>set</strong>(value = NULL) { ... } ⇒ IVar </a>
</span>
<span class="summary_desc"><div class='inline'><p>Set the <code>IVar</code> to a value and wake or notify all threads waiting on it.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#wait_or_cancel-instance_method" title="#wait_or_cancel (instance method)">#<strong>wait_or_cancel</strong>(timeout) ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Wait the given number of seconds for the operation to complete.</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::Future (class)">Future</a></span></tt>
</h3><div class="docstring">
<div class="discussion">
<p>Create a new <code>Future</code> in the <code>:unscheduled</code> state.</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 used to define the behavior at update and deref
and to specify the executor on which to perform actions</p>
</div>
</li>
</ul>
<p class="tag_title">Options Hash (<tt>opts</tt>):</p>
<ul class="option">
<li>
<span class="name">:executor</span>
<span class="type">(<tt>Executor</tt>)</span>
<span class="default">
</span>
— <div class='inline'><p>when set use the given <code>Executor</code> instance.
Three special values are also supported: <code>:io</code> returns the global pool for
long, blocking (IO) tasks, <code>:fast</code> returns the global pool for short, fast
operations, and <code>:immediate</code> returns the global <code>ImmediateExecutor</code> object.</p>
</div>
</li>
<li>
<span class="name">:dup_on_deref</span>
<span class="type">(<tt>Boolean</tt>)</span>
<span class="default">
— default:
<tt>false</tt>
</span>
— <div class='inline'><p>Call <code>#dup</code> before
returning the data from <span class='object_link'><a href="Concern/Obligation.html#value-instance_method" title="Concurrent::Concern::Obligation#value (method)">Concern::Obligation#value</a></span></p>
</div>
</li>
<li>
<span class="name">:freeze_on_deref</span>
<span class="type">(<tt>Boolean</tt>)</span>
<span class="default">
— default:
<tt>false</tt>
</span>
— <div class='inline'><p>Call <code>#freeze</code> before
returning the data from <span class='object_link'><a href="Concern/Obligation.html#value-instance_method" title="Concurrent::Concern::Obligation#value (method)">Concern::Obligation#value</a></span></p>
</div>
</li>
<li>
<span class="name">:copy_on_deref</span>
<span class="type">(<tt>Proc</tt>)</span>
<span class="default">
— default:
<tt>nil</tt>
</span>
— <div class='inline'><p>When calling the <span class='object_link'><a href="Concern/Obligation.html#value-instance_method" title="Concurrent::Concern::Obligation#value (method)">Concern::Obligation#value</a></span>
method, call the given proc passing the internal value as the sole
argument then return the new value returned from the proc.</p>
</div>
</li>
<li>
<span class="name">:args</span>
<span class="type">(<tt>object</tt>, <tt><span class='object_link'><a href="Array.html" title="Concurrent::Array (class)">Array</a></span></tt>)</span>
<span class="default">
</span>
— <div class='inline'><p>zero or more arguments to be passed the task
block on execution</p>
</div>
</li>
</ul>
<p class="tag_title">Yields:</p>
<ul class="yield">
<li>
<span class='type'></span>
<div class='inline'><p>the asynchronous operation to perform</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 no block is given</p>
</div>
</li>
</ul>
</div><table class="source_code">
<tr>
<td>
<pre class="lines">
33
34
35
36</pre>
</td>
<td>
<pre class="code"><span class="info file"># File 'lib/concurrent/future.rb', line 33</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='comma'>,</span> <span class='op'>&</span><span class='id identifier rubyid_block'>block</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'>no block given</span><span class='tstring_end'>'</span></span><span class='rparen'>)</span> <span class='kw'>unless</span> <span class='id identifier rubyid_block_given?'>block_given?</span>
<span class='kw'>super</span><span class='lparen'>(</span><span class='const'>NULL</span><span class='comma'>,</span> <span class='id identifier rubyid_opts'>opts</span><span class='period'>.</span><span class='id identifier rubyid_merge'>merge</span><span class='lparen'>(</span><span class='label'>__task_from_block__:</span> <span class='id identifier rubyid_block'>block</span><span class='rparen'>)</span><span class='comma'>,</span> <span class='op'>&</span><span class='kw'>nil</span><span class='rparen'>)</span>
<span class='kw'>end</span></pre>
</td>
</tr>
</table>
</div>
</div>
<div id="class_method_details" class="method_details_list">
<h2>Class Method Details</h2>
<div class="method_details first">
<h3 class="signature first" id="execute-class_method">
.<strong>execute</strong>(opts = {}) { ... } ⇒ <tt><span class='object_link'><a href="" title="Concurrent::Future (class)">Future</a></span></tt>
</h3><div class="docstring">
<div class="discussion">
<p>Create a new <code>Future</code> object with the given block, execute it, and return the
<code>:pending</code> object.</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_future'>future</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="" title="Concurrent::Future (class)">Future</a></span></span><span class='period'>.</span><span class='id identifier rubyid_execute'>execute</span><span class='lbrace'>{</span> <span class='id identifier rubyid_sleep'>sleep</span><span class='lparen'>(</span><span class='int'>1</span><span class='rparen'>)</span><span class='semicolon'>;</span> <span class='int'>42</span> <span class='rbrace'>}</span>
<span class='id identifier rubyid_future'>future</span><span class='period'>.</span><span class='id identifier rubyid_state'>state</span> <span class='comment'>#=> :pending</span></code></pre>
</div>
<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 used to define the behavior at update and deref
and to specify the executor on which to perform actions</p>
</div>
</li>
</ul>
<p class="tag_title">Options Hash (<tt>opts</tt>):</p>
<ul class="option">
<li>
<span class="name">:executor</span>
<span class="type">(<tt>Executor</tt>)</span>
<span class="default">
</span>
— <div class='inline'><p>when set use the given <code>Executor</code> instance.
Three special values are also supported: <code>:io</code> returns the global pool for
long, blocking (IO) tasks, <code>:fast</code> returns the global pool for short, fast
operations, and <code>:immediate</code> returns the global <code>ImmediateExecutor</code> object.</p>
</div>
</li>
<li>
<span class="name">:dup_on_deref</span>
<span class="type">(<tt>Boolean</tt>)</span>
<span class="default">
— default:
<tt>false</tt>
</span>
— <div class='inline'><p>Call <code>#dup</code> before
returning the data from <span class='object_link'><a href="Concern/Obligation.html#value-instance_method" title="Concurrent::Concern::Obligation#value (method)">Concern::Obligation#value</a></span></p>
</div>
</li>
<li>
<span class="name">:freeze_on_deref</span>
<span class="type">(<tt>Boolean</tt>)</span>
<span class="default">
— default:
<tt>false</tt>
</span>
— <div class='inline'><p>Call <code>#freeze</code> before
returning the data from <span class='object_link'><a href="Concern/Obligation.html#value-instance_method" title="Concurrent::Concern::Obligation#value (method)">Concern::Obligation#value</a></span></p>
</div>
</li>
<li>
<span class="name">:copy_on_deref</span>
<span class="type">(<tt>Proc</tt>)</span>
<span class="default">
— default:
<tt>nil</tt>
</span>
— <div class='inline'><p>When calling the <span class='object_link'><a href="Concern/Obligation.html#value-instance_method" title="Concurrent::Concern::Obligation#value (method)">Concern::Obligation#value</a></span>
method, call the given proc passing the internal value as the sole
argument then return the new value returned from the proc.</p>
</div>
</li>
<li>
<span class="name">:args</span>
<span class="type">(<tt>object</tt>, <tt><span class='object_link'><a href="Array.html" title="Concurrent::Array (class)">Array</a></span></tt>)</span>
<span class="default">
</span>
— <div class='inline'><p>zero or more arguments to be passed the task
block on execution</p>
</div>
</li>
</ul>
<p class="tag_title">Yields:</p>
<ul class="yield">
<li>
<span class='type'></span>
<div class='inline'><p>the asynchronous operation to perform</p>
</div>
</li>
</ul>
<p class="tag_title">Returns:</p>
<ul class="return">
<li>
<span class='type'>(<tt><span class='object_link'><a href="" title="Concurrent::Future (class)">Future</a></span></tt>)</span>
—
<div class='inline'><p>the newly created <code>Future</code> in the <code>:pending</code> state</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 no block is given</p>
</div>
</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/future.rb', line 77</span>
<span class='kw'>def</span> <span class='kw'>self</span><span class='period'>.</span><span class='id identifier rubyid_execute'>execute</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='comma'>,</span> <span class='op'>&</span><span class='id identifier rubyid_block'>block</span><span class='rparen'>)</span>
<span class='const'><span class='object_link'><a href="" title="Concurrent::Future (class)">Future</a></span></span><span class='period'>.</span><span class='id identifier rubyid_new'><span class='object_link'><a href="#initialize-instance_method" title="Concurrent::Future#initialize (method)">new</a></span></span><span class='lparen'>(</span><span class='id identifier rubyid_opts'>opts</span><span class='comma'>,</span> <span class='op'>&</span><span class='id identifier rubyid_block'>block</span><span class='rparen'>)</span><span class='period'>.</span><span class='id identifier rubyid_execute'>execute</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="cancel-instance_method">
#<strong>cancel</strong> ⇒ <tt>Boolean</tt>
</h3><div class="docstring">
<div class="discussion">
<p>Attempt to cancel the operation if it has not already processed.
The operation can only be cancelled while still <code>pending</code>. It cannot
be cancelled once it has begun processing or has completed.</p>
</div>
</div>
<div class="tags">
<p class="tag_title">Returns:</p>
<ul class="return">
<li>
<span class='type'>(<tt>Boolean</tt>)</span>
—
<div class='inline'><p>was the operation successfully cancelled.</p>
</div>
</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/future.rb', line 99</span>
<span class='kw'>def</span> <span class='id identifier rubyid_cancel'>cancel</span>
<span class='kw'>if</span> <span class='id identifier rubyid_compare_and_set_state'>compare_and_set_state</span><span class='lparen'>(</span><span class='symbol'>:cancelled</span><span class='comma'>,</span> <span class='symbol'>:pending</span><span class='rparen'>)</span>
<span class='id identifier rubyid_complete'>complete</span><span class='lparen'>(</span><span class='kw'>false</span><span class='comma'>,</span> <span class='kw'>nil</span><span class='comma'>,</span> <span class='const'><span class='object_link'><a href="../Concurrent.html#CancelledOperationError-constant" title="Concurrent::CancelledOperationError (constant)">CancelledOperationError</a></span></span><span class='period'>.</span><span class='id identifier rubyid_new'>new</span><span class='rparen'>)</span>
<span class='kw'>true</span>
<span class='kw'>else</span>
<span class='kw'>false</span>
<span class='kw'>end</span>
<span class='kw'>end</span></pre>
</td>
</tr>
</table>
</div>
<div class="method_details ">
<h3 class="signature " id="cancelled?-instance_method">
#<strong>cancelled?</strong> ⇒ <tt>Boolean</tt>
</h3><div class="docstring">
<div class="discussion">
<p>Has the operation been successfully cancelled?</p>
</div>
</div>
<div class="tags">
<p class="tag_title">Returns:</p>
<ul class="return">
<li>
<span class='type'>(<tt>Boolean</tt>)</span>
</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/future.rb', line 111</span>
<span class='kw'>def</span> <span class='id identifier rubyid_cancelled?'>cancelled?</span>
<span class='id identifier rubyid_state'>state</span> <span class='op'>==</span> <span class='symbol'>:cancelled</span>
<span class='kw'>end</span></pre>
</td>
</tr>
</table>
</div>
<div class="method_details ">
<h3 class="signature " id="execute-instance_method">
#<strong>execute</strong> ⇒ <tt><span class='object_link'><a href="" title="Concurrent::Future (class)">Future</a></span></tt>
</h3><div class="docstring">
<div class="discussion">
<p>Execute an <code>:unscheduled</code> <code>Future</code>. Immediately sets the state to <code>:pending</code> and
passes the block to a new thread/thread pool for eventual execution.
Does nothing if the <code>Future</code> is in any state other than <code>:unscheduled</code>.</p>
</div>
</div>
<div class="tags">
<div class="examples">
<p class="tag_title">Examples:</p>
<p class="example_title"><div class='inline'><p>Instance and execute in separate steps</p>
</div></p>
<pre class="example code"><code><span class='id identifier rubyid_future'>future</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="" title="Concurrent::Future (class)">Future</a></span></span><span class='period'>.</span><span class='id identifier rubyid_new'><span class='object_link'><a href="#initialize-instance_method" title="Concurrent::Future#initialize (method)">new</a></span></span><span class='lbrace'>{</span> <span class='id identifier rubyid_sleep'>sleep</span><span class='lparen'>(</span><span class='int'>1</span><span class='rparen'>)</span><span class='semicolon'>;</span> <span class='int'>42</span> <span class='rbrace'>}</span>
<span class='id identifier rubyid_future'>future</span><span class='period'>.</span><span class='id identifier rubyid_state'>state</span> <span class='comment'>#=> :unscheduled
</span><span class='id identifier rubyid_future'>future</span><span class='period'>.</span><span class='id identifier rubyid_execute'>execute</span>
<span class='id identifier rubyid_future'>future</span><span class='period'>.</span><span class='id identifier rubyid_state'>state</span> <span class='comment'>#=> :pending</span></code></pre>
<p class="example_title"><div class='inline'><p>Instance and execute in one line</p>
</div></p>
<pre class="example code"><code><span class='id identifier rubyid_future'>future</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="" title="Concurrent::Future (class)">Future</a></span></span><span class='period'>.</span><span class='id identifier rubyid_new'><span class='object_link'><a href="#initialize-instance_method" title="Concurrent::Future#initialize (method)">new</a></span></span><span class='lbrace'>{</span> <span class='id identifier rubyid_sleep'>sleep</span><span class='lparen'>(</span><span class='int'>1</span><span class='rparen'>)</span><span class='semicolon'>;</span> <span class='int'>42</span> <span class='rbrace'>}</span><span class='period'>.</span><span class='id identifier rubyid_execute'>execute</span>
<span class='id identifier rubyid_future'>future</span><span class='period'>.</span><span class='id identifier rubyid_state'>state</span> <span class='comment'>#=> :pending</span></code></pre>
</div>
<p class="tag_title">Returns:</p>
<ul class="return">
<li>
<span class='type'>(<tt><span class='object_link'><a href="" title="Concurrent::Future (class)">Future</a></span></tt>)</span>
—
<div class='inline'><p>a reference to <code>self</code></p>
</div>
</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/future.rb', line 53</span>
<span class='kw'>def</span> <span class='id identifier rubyid_execute'>execute</span>
<span class='kw'>if</span> <span class='id identifier rubyid_compare_and_set_state'>compare_and_set_state</span><span class='lparen'>(</span><span class='symbol'>:pending</span><span class='comma'>,</span> <span class='symbol'>:unscheduled</span><span class='rparen'>)</span>
<span class='ivar'>@executor</span><span class='period'>.</span><span class='id identifier rubyid_post'>post</span><span class='lbrace'>{</span> <span class='id identifier rubyid_safe_execute'>safe_execute</span><span class='lparen'>(</span><span class='ivar'>@task</span><span class='comma'>,</span> <span class='ivar'>@args</span><span class='rparen'>)</span> <span class='rbrace'>}</span>
<span class='kw'>self</span>
<span class='kw'>end</span>
<span class='kw'>end</span></pre>
</td>
</tr>
</table>
</div>
<div class="method_details ">
<h3 class="signature " id="set-instance_method">
#<strong>set</strong>(value = NULL) { ... } ⇒ <tt><span class='object_link'><a href="IVar.html" title="Concurrent::IVar (class)">IVar</a></span></tt>
</h3><div class="docstring">
<div class="discussion">
<p>Set the <code>IVar</code> to a value and wake or notify all threads waiting on it.</p>
</div>
</div>
<div class="tags">
<p class="tag_title">Parameters:</p>
<ul class="param">
<li>
<span class='name'>value</span>
<span class='type'>(<tt>Object</tt>)</span>
<em class="default">(defaults to: <tt>NULL</tt>)</em>
—
<div class='inline'><p>the value to store in the <code>IVar</code></p>
</div>
</li>
</ul>
<p class="tag_title">Yields:</p>
<ul class="yield">
<li>
<span class='type'></span>
<div class='inline'><p>A block operation to use for setting the value</p>
</div>
</li>
</ul>
<p class="tag_title">Returns:</p>
<ul class="return">
<li>
<span class='type'>(<tt><span class='object_link'><a href="IVar.html" title="Concurrent::IVar (class)">IVar</a></span></tt>)</span>
—
<div class='inline'><p>self</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 both a value and a block are given</p>
</div>
</li>
<li>
<span class='type'>(<tt><span class='object_link'><a href="MultipleAssignmentError.html" title="Concurrent::MultipleAssignmentError (class)">Concurrent::MultipleAssignmentError</a></span></tt>)</span>
—
<div class='inline'><p>if the <code>IVar</code> has already
been set or otherwise completed</p>
</div>
</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/future.rb', line 82</span>
<span class='kw'>def</span> <span class='id identifier rubyid_set'>set</span><span class='lparen'>(</span><span class='id identifier rubyid_value'>value</span> <span class='op'>=</span> <span class='const'>NULL</span><span class='comma'>,</span> <span class='op'>&</span><span class='id identifier rubyid_block'>block</span><span class='rparen'>)</span>
<span class='id identifier rubyid_check_for_block_or_value!'>check_for_block_or_value!</span><span class='lparen'>(</span><span class='id identifier rubyid_block_given?'>block_given?</span><span class='comma'>,</span> <span class='id identifier rubyid_value'>value</span><span class='rparen'>)</span>
<span class='id identifier rubyid_synchronize'>synchronize</span> <span class='kw'>do</span>
<span class='kw'>if</span> <span class='ivar'>@state</span> <span class='op'>!=</span> <span class='symbol'>:unscheduled</span>
<span class='id identifier rubyid_raise'>raise</span> <span class='const'><span class='object_link'><a href="MultipleAssignmentError.html" title="Concurrent::MultipleAssignmentError (class)">MultipleAssignmentError</a></span></span>
<span class='kw'>else</span>
<span class='ivar'>@task</span> <span class='op'>=</span> <span class='id identifier rubyid_block'>block</span> <span class='op'>||</span> <span class='const'>Proc</span><span class='period'>.</span><span class='id identifier rubyid_new'>new</span> <span class='lbrace'>{</span> <span class='id identifier rubyid_value'>value</span> <span class='rbrace'>}</span>
<span class='kw'>end</span>
<span class='kw'>end</span>
<span class='id identifier rubyid_execute'>execute</span>
<span class='kw'>end</span></pre>
</td>
</tr>
</table>
</div>
<div class="method_details ">
<h3 class="signature " id="wait_or_cancel-instance_method">
#<strong>wait_or_cancel</strong>(timeout) ⇒ <tt>Boolean</tt>
</h3><div class="docstring">
<div class="discussion">
<p>Wait the given number of seconds for the operation to complete.
On timeout attempt to cancel the operation.</p>
</div>
</div>
<div class="tags">
<p class="tag_title">Parameters:</p>
<ul class="param">
<li>
<span class='name'>timeout</span>
<span class='type'>(<tt>Numeric</tt>)</span>
—
<div class='inline'><p>the maximum time in seconds to wait.</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>true if the operation completed before the timeout
else false</p>
</div>
</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/future.rb', line 121</span>
<span class='kw'>def</span> <span class='id identifier rubyid_wait_or_cancel'>wait_or_cancel</span><span class='lparen'>(</span><span class='id identifier rubyid_timeout'>timeout</span><span class='rparen'>)</span>
<span class='id identifier rubyid_wait'>wait</span><span class='lparen'>(</span><span class='id identifier rubyid_timeout'>timeout</span><span class='rparen'>)</span>
<span class='kw'>if</span> <span class='id identifier rubyid_complete?'>complete?</span>
<span class='kw'>true</span>
<span class='kw'>else</span>
<span class='id identifier rubyid_cancel'>cancel</span>
<span class='kw'>false</span>
<span class='kw'>end</span>
<span class='kw'>end</span></pre>
</td>
</tr>
</table>
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