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Exchanger.html
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Exchanger.html
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<!DOCTYPE html>
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Class: Concurrent::Exchanger
— Concurrent Ruby
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<div id="content"><h1>Class: Concurrent::Exchanger
</h1>
<div class="box_info">
<dl>
<dt>Inherits:</dt>
<dd>
<span class="inheritName"><span class='object_link'>ExchangerImplementation</span></span>
<ul class="fullTree">
<li>Object</li>
<li class="next">Concurrent::Exchanger</li>
</ul>
<a href="#" class="inheritanceTree">show all</a>
</dd>
</dl>
<dl>
<dt>Defined in:</dt>
<dd>lib/concurrent/exchanger.rb</dd>
</dl>
</div>
<h2>Overview</h2><div class="docstring">
<div class="discussion">
<p>A synchronization point at which threads can pair and swap elements within
pairs. Each thread presents some object on entry to the exchange method,
matches with a partner thread, and receives its partner's object on return.</p>
<h2>Thread-safe Variable Classes</h2>
<p>Each of the thread-safe variable classes is designed to solve a different
problem. In general:</p>
<ul>
<li><em><span class='object_link'><a href="Agent.html" title="Concurrent::Agent (class)">Agent</a></span>:</em> Shared, mutable variable providing independent,
uncoordinated, <em>asynchronous</em> change of individual values. Best used when
the value will undergo frequent, complex updates. Suitable when the result
of an update does not need to be known immediately.</li>
<li><em><span class='object_link'><a href="Atom.html" title="Concurrent::Atom (class)">Atom</a></span>:</em> Shared, mutable variable providing independent,
uncoordinated, <em>synchronous</em> change of individual values. Best used when
the value will undergo frequent reads but only occasional, though complex,
updates. Suitable when the result of an update must be known immediately.</li>
<li><em><span class='object_link'><a href="AtomicReference.html" title="Concurrent::AtomicReference (class)">AtomicReference</a></span>:</em> A simple object reference that can be
atomically. Updates are synchronous but fast. Best used when updates a
simple set operations. Not suitable when updates are complex.
<span class='object_link'><a href="AtomicBoolean.html" title="Concurrent::AtomicBoolean (class)">AtomicBoolean</a></span> and <span class='object_link'><a href="AtomicFixnum.html" title="Concurrent::AtomicFixnum (class)">AtomicFixnum</a></span> are similar
but optimized for the given data type.</li>
<li><em><span class='object_link'><a href="" title="Concurrent::Exchanger (class)">Exchanger</a></span>:</em> Shared, stateless synchronization point. Used
when two or more threads need to exchange data. The threads will pair then
block on each other until the exchange is complete.</li>
<li><em><span class='object_link'><a href="MVar.html" title="Concurrent::MVar (class)">MVar</a></span>:</em> Shared synchronization point. Used when one thread
must give a value to another, which must take the value. The threads will
block on each other until the exchange is complete.</li>
<li><em><span class='object_link'><a href="ThreadLocalVar.html" title="Concurrent::ThreadLocalVar (class)">ThreadLocalVar</a></span>:</em> Shared, mutable, isolated variable which
holds a different value for each thread which has access. Often used as
an instance variable in objects which must maintain different state
for different threads.</li>
<li><em><span class='object_link'><a href="TVar.html" title="Concurrent::TVar (class)">TVar</a></span>:</em> Shared, mutable variables which provide
<em>coordinated</em>, <em>synchronous</em>, change of <em>many</em> stated. Used when multiple
value must change together, in an all-or-nothing transaction.
This implementation is very simple, using only a single slot for each
exchanger (unlike more advanced implementations which use an "arena").
This approach will work perfectly fine when there are only a few threads
accessing a single <code>Exchanger</code>. Beyond a handful of threads the performance
will degrade rapidly due to contention on the single slot, but the algorithm
will remain correct.</li>
</ul>
</div>
</div>
<div class="tags">
<div class="examples">
<p class="tag_title">Examples:</p>
<pre class="example code"><code>
<span class='id identifier rubyid_exchanger'>exchanger</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'>Exchanger</span><span class='period'>.</span><span class='id identifier rubyid_new'><span class='object_link'><a href="#initialize-instance_method" title="Concurrent::Exchanger#initialize (method)">new</a></span></span>
<span class='id identifier rubyid_threads'>threads</span> <span class='op'>=</span> <span class='lbracket'>[</span>
<span class='const'>Thread</span><span class='period'>.</span><span class='id identifier rubyid_new'>new</span> <span class='lbrace'>{</span> <span class='id identifier rubyid_puts'>puts</span> <span class='tstring'><span class='tstring_beg'>"</span><span class='tstring_content'>first: </span><span class='tstring_end'>"</span></span> <span class='op'><<</span> <span class='id identifier rubyid_exchanger'>exchanger</span><span class='period'>.</span><span class='id identifier rubyid_exchange'>exchange</span><span class='lparen'>(</span><span class='tstring'><span class='tstring_beg'>'</span><span class='tstring_content'>foo</span><span class='tstring_end'>'</span></span><span class='comma'>,</span> <span class='int'>1</span><span class='rparen'>)</span> <span class='rbrace'>}</span><span class='comma'>,</span> <span class='comment'>#=> "first: bar"
</span> <span class='const'>Thread</span><span class='period'>.</span><span class='id identifier rubyid_new'>new</span> <span class='lbrace'>{</span> <span class='id identifier rubyid_puts'>puts</span> <span class='tstring'><span class='tstring_beg'>"</span><span class='tstring_content'>second: </span><span class='tstring_end'>"</span></span> <span class='op'><<</span> <span class='id identifier rubyid_exchanger'>exchanger</span><span class='period'>.</span><span class='id identifier rubyid_exchange'>exchange</span><span class='lparen'>(</span><span class='tstring'><span class='tstring_beg'>'</span><span class='tstring_content'>bar</span><span class='tstring_end'>'</span></span><span class='comma'>,</span> <span class='int'>1</span><span class='rparen'>)</span> <span class='rbrace'>}</span> <span class='comment'>#=> "second: foo"
</span><span class='rbracket'>]</span>
<span class='id identifier rubyid_threads'>threads</span><span class='period'>.</span><span class='id identifier rubyid_each'>each</span> <span class='lbrace'>{</span><span class='op'>|</span><span class='id identifier rubyid_t'>t</span><span class='op'>|</span> <span class='id identifier rubyid_t'>t</span><span class='period'>.</span><span class='id identifier rubyid_join'>join</span><span class='lparen'>(</span><span class='int'>2</span><span class='rparen'>)</span> <span class='rbrace'>}</span></code></pre>
</div>
<p class="tag_title">See Also:</p>
<ul class="see">
<li><a href="http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Exchanger.html" target="_parent" title="java.util.concurrent.Exchanger">java.util.concurrent.Exchanger</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="#exchange-instance_method" title="#exchange (instance method)">#<strong>exchange</strong>(value, timeout = nil) ⇒ Object </a>
</span>
<span class="summary_desc"><div class='inline'><p>Waits for another thread to arrive at this exchange point (unless the current thread is interrupted), and then transfers the given object to it, receiving its object in return.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#exchange!-instance_method" title="#exchange! (instance method)">#<strong>exchange!</strong>(value, timeout = nil) ⇒ Object </a>
</span>
<span class="summary_desc"><div class='inline'><p>Waits for another thread to arrive at this exchange point (unless the current thread is interrupted), and then transfers the given object to it, receiving its object in return.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#initialize-instance_method" title="#initialize (instance method)">#<strong>initialize</strong> ⇒ undocumented </a>
</span>
<span class="note title constructor">constructor</span>
<span class="summary_desc"><div class='inline'><p>Creates exchanger instance.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#try_exchange-instance_method" title="#try_exchange (instance method)">#<strong>try_exchange</strong>(value, timeout = nil) ⇒ Concurrent::Maybe </a>
</span>
<span class="summary_desc"><div class='inline'><p>Waits for another thread to arrive at this exchange point (unless the current thread is interrupted), and then transfers the given object to it, receiving its object in return.</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> ⇒ <tt>undocumented</tt>
</h3><div class="docstring">
<div class="discussion">
<p>Creates exchanger instance</p>
</div>
</div>
<div class="tags">
</div><table class="source_code">
<tr>
<td>
<pre class="lines">
</pre>
</td>
<td>
<pre class="code"><span class="info file"># File 'lib/concurrent/exchanger.rb', line 333</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="exchange-instance_method">
#<strong>exchange</strong>(value, timeout = nil) ⇒ <tt>Object</tt>
</h3><div class="docstring">
<div class="discussion">
<p>Waits for another thread to arrive at this exchange point (unless the
current thread is interrupted), and then transfers the given object to
it, receiving its object in return. The timeout value indicates the
approximate number of seconds the method should block while waiting
for the exchange. When the timeout value is <code>nil</code> the method will
block indefinitely.</p>
<p>In some edge cases when a <code>timeout</code> is given a return value of <code>nil</code> may be
ambiguous. Specifically, if <code>nil</code> is a valid value in the exchange it will
be impossible to tell whether <code>nil</code> is the actual return value or if it
signifies timeout. When <code>nil</code> is a valid value in the exchange consider
using <span class='object_link'><a href="#exchange!-instance_method" title="Concurrent::Exchanger#exchange! (method)">#exchange!</a></span> or <span class='object_link'><a href="#try_exchange-instance_method" title="Concurrent::Exchanger#try_exchange (method)">#try_exchange</a></span> instead.</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>
—
<div class='inline'><p>the value to exchange with another thread</p>
</div>
</li>
<li>
<span class='name'>timeout</span>
<span class='type'>(<tt>Numeric</tt>, <tt>nil</tt>)</span>
<em class="default">(defaults to: <tt>nil</tt>)</em>
—
<div class='inline'><p>in seconds, <code>nil</code> blocks indefinitely</p>
</div>
</li>
</ul>
<p class="tag_title">Returns:</p>
<ul class="return">
<li>
<span class='type'>(<tt>Object</tt>)</span>
—
<div class='inline'><p>the value exchanged by the other thread or <code>nil</code> on timeout</p>
</div>
</li>
</ul>
</div><table class="source_code">
<tr>
<td>
<pre class="lines">
</pre>
</td>
<td>
<pre class="code"><span class="info file"># File 'lib/concurrent/exchanger.rb', line 336</span>
</pre>
</td>
</tr>
</table>
</div>
<div class="method_details ">
<h3 class="signature " id="exchange!-instance_method">
#<strong>exchange!</strong>(value, timeout = nil) ⇒ <tt>Object</tt>
</h3><div class="docstring">
<div class="discussion">
<p>Waits for another thread to arrive at this exchange point (unless the
current thread is interrupted), and then transfers the given object to
it, receiving its object in return. The timeout value indicates the
approximate number of seconds the method should block while waiting
for the exchange. When the timeout value is <code>nil</code> the method will
block indefinitely.</p>
<p>On timeout a <span class='object_link'><a href="../Concurrent.html#TimeoutError-constant" title="Concurrent::TimeoutError (constant)">TimeoutError</a></span> exception will be raised.</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>
—
<div class='inline'><p>the value to exchange with another thread</p>
</div>
</li>
<li>
<span class='name'>timeout</span>
<span class='type'>(<tt>Numeric</tt>, <tt>nil</tt>)</span>
<em class="default">(defaults to: <tt>nil</tt>)</em>
—
<div class='inline'><p>in seconds, <code>nil</code> blocks indefinitely</p>
</div>
</li>
</ul>
<p class="tag_title">Returns:</p>
<ul class="return">
<li>
<span class='type'>(<tt>Object</tt>)</span>
—
<div class='inline'><p>the value exchanged by the other thread</p>
</div>
</li>
</ul>
<p class="tag_title">Raises:</p>
<ul class="raise">
<li>
<span class='type'>(<tt><span class='object_link'><a href="../Concurrent.html#TimeoutError-constant" title="Concurrent::TimeoutError (constant)">Concurrent::TimeoutError</a></span></tt>)</span>
—
<div class='inline'><p>on timeout</p>
</div>
</li>
</ul>
</div><table class="source_code">
<tr>
<td>
<pre class="lines">
</pre>
</td>
<td>
<pre class="code"><span class="info file"># File 'lib/concurrent/exchanger.rb', line 340</span>
</pre>
</td>
</tr>
</table>
</div>
<div class="method_details ">
<h3 class="signature " id="try_exchange-instance_method">
#<strong>try_exchange</strong>(value, timeout = nil) ⇒ <tt><span class='object_link'><a href="Maybe.html" title="Concurrent::Maybe (class)">Concurrent::Maybe</a></span></tt>
</h3><div class="docstring">
<div class="discussion">
<p>Waits for another thread to arrive at this exchange point (unless the
current thread is interrupted), and then transfers the given object to
it, receiving its object in return. The timeout value indicates the
approximate number of seconds the method should block while waiting
for the exchange. When the timeout value is <code>nil</code> the method will
block indefinitely.</p>
<p>The return value will be a <span class='object_link'><a href="Maybe.html" title="Concurrent::Maybe (class)">Maybe</a></span> set to <code>Just</code> on success or
<code>Nothing</code> on timeout.</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_exchanger'>exchanger</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::Exchanger (class)">Exchanger</a></span></span><span class='period'>.</span><span class='id identifier rubyid_new'><span class='object_link'><a href="#initialize-instance_method" title="Concurrent::Exchanger#initialize (method)">new</a></span></span>
<span class='id identifier rubyid_result'>result</span> <span class='op'>=</span> <span class='id identifier rubyid_exchanger'>exchanger</span><span class='period'>.</span><span class='id identifier rubyid_exchange'>exchange</span><span class='lparen'>(</span><span class='symbol'>:foo</span><span class='comma'>,</span> <span class='float'>0.5</span><span class='rparen'>)</span>
<span class='kw'>if</span> <span class='id identifier rubyid_result'>result</span><span class='period'>.</span><span class='id identifier rubyid_just?'>just?</span>
<span class='id identifier rubyid_puts'>puts</span> <span class='id identifier rubyid_result'>result</span><span class='period'>.</span><span class='id identifier rubyid_value'>value</span> <span class='comment'>#=> :bar
</span><span class='kw'>else</span>
<span class='id identifier rubyid_puts'>puts</span> <span class='tstring'><span class='tstring_beg'>'</span><span class='tstring_content'>timeout</span><span class='tstring_end'>'</span></span>
<span class='kw'>end</span></code></pre>
</div>
<p class="tag_title">Parameters:</p>
<ul class="param">
<li>
<span class='name'>value</span>
<span class='type'>(<tt>Object</tt>)</span>
—
<div class='inline'><p>the value to exchange with another thread</p>
</div>
</li>
<li>
<span class='name'>timeout</span>
<span class='type'>(<tt>Numeric</tt>, <tt>nil</tt>)</span>
<em class="default">(defaults to: <tt>nil</tt>)</em>
—
<div class='inline'><p>in seconds, <code>nil</code> blocks indefinitely</p>
</div>
</li>
</ul>
<p class="tag_title">Returns:</p>
<ul class="return">
<li>
<span class='type'>(<tt><span class='object_link'><a href="Maybe.html" title="Concurrent::Maybe (class)">Concurrent::Maybe</a></span></tt>)</span>
—
<div class='inline'><p>on success a <code>Just</code> maybe will be returned with
the item exchanged by the other thread as <code>#value</code>; on timeout a
<code>Nothing</code> maybe will be returned with <span class='object_link'><a href="../Concurrent.html#TimeoutError-constant" title="Concurrent::TimeoutError (constant)">TimeoutError</a></span> as <code>#reason</code></p>
</div>
</li>
</ul>
</div><table class="source_code">
<tr>
<td>
<pre class="lines">
</pre>
</td>
<td>
<pre class="code"><span class="info file"># File 'lib/concurrent/exchanger.rb', line 347</span>
</pre>
</td>
</tr>
</table>
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