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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-ruby/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 updated
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="../Concurrent.html#initialize-instance_method" title="Concurrent#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>
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