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<meta name="keywords" content="threads, BTL, thread library, C++">
<title>Boost.Threads, atomic_t</title>
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<table border="0" cellpadding="7" cellspacing="0" width="100%">
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<h3><img src="../../../c++boost.gif" alt="C++ Boost" width="277" height="86"></h3>
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<td valign="top">
<h1 align="center">Boost.Threads</h1>
<h2 align="center">atomic_t</h2>
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</tr>
</table>
<hr>
<h2>Header</h2>
<p>The <tt>atomic_t</tt> class defines an "atomic integer" type. This class should be used
to perform thread safe operations on an integral type with out the overhead of locks. Only
a limited set of integer operations are available with an <tt>atomic_t</tt> instance.</p>
<pre>
#include <boost/thread/atomic.hpp>
</pre>
<h2>Public Interface</h2>
<pre>
class atomic_t
{
public:
typedef <b>implementation defined</b> value_type;
explicit atomic_t(value_type val=0);
};
atomic_t::value_type read(const atomic_t& x);
atomic_t::value_type increment(atomic_t& x);
atomic_t::value_type decrement(atomic_t& x);
atomic_t::value_type swap(atomic_t& x, atomic_t::value_type y);
atomic_t::value_type compare_swap(atomic_t& x, atomic_t::value_type y, atomic_t::value_type z);
</pre>
<h3>Constructor</h3>
<pre>
atomic_t(atomic_t::value_type val=0);
</pre>
<p>Constructs an <tt>atomic_t</tt> and sets its value to <tt>val</tt>.</p>
<h3>read</h3>
<pre>
atomic_t::value_type read(const atomic_t& x);
</pre>
<p>Gets the current value of <tt>x</tt>.</p>
<h3>increment</h3>
<pre>
atomic_t::value_type increment(atomic_t& x);
</pre>
<p>Increments <tt>x</tt> and returns a value <tt>< 0</tt> if the result is less than 0,
<tt>> 0</tt> if the result is greater than 0 and <tt>== 0</tt> if the result is equal to
0.</p>
<h3>decrement</h3>
<pre>
atomic_t::value_type decrement(atomic_t& x);
</pre>
<p>Decrements <tt>x</tt> and returns a value <tt>< 0</tt> if the result is less than 0,
<tt>> 0</tt> if the result is greater than 0 and <tt>== 0</tt> if the result is equal to
0.</p>
<h3>swap</h3>
<pre>
atomic_t::value_type swap(atomic_t& x, atomic_t::value_type y);
</pre>
<p>Assigns the value of <tt>y</tt> to <tt>x</tt> and returns the value of <tt>x</tt> prior
to the swap.</p>
<h3>compare_swap</h3>
<pre>
atomic_t::value_type compare_swap(atomic_t& x, atomic_t::value_type y, atomic_t::value_type z);
</pre>
<p>Compares the value of <tt>z</tt> to the value of <tt>x</tt> and if equal sets the value of
<tt>x</tt> to the value of <tt>y</tt> and returns the value of <tt>x</tt> prior to the swap.</p>
<h2>Example Usage</h2>
<pre>
#include <boost/thread/atomic.hpp>
#include <boost/test/test_tools.hpp>
int test_main(int, char*[])
{
boost::atomic_t a;
BOOST_TEST_VERIFY(boost::read(a) == 0);
BOOST_TEST_VERIFY(boost::increment(a) > 0);
BOOST_TEST_VERIFY(boost::decrement(a) == 0);
BOOST_TEST_VERIFY(boost::swap(a, 1) == 0);
BOOST_TEST_VERIFY(boost::swap(a, 2, 0) == 1);
BOOST_TEST_VERIFY(boost::read(a) == 1);
}
</pre>
<hr>
<p>Revised <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->05 November, 2001<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i> Copyright <a href="mailto:williamkempf@hotmail.com">William E. Kempf</a>
2001 all rights reserved.</i></p>
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