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164 lines
4.4 KiB
HTML
164 lines
4.4 KiB
HTML
<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<meta name="keywords" content="threads, BTL, thread library, C++">
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<title>Boost.Threads, basic_trylock</title>
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</head>
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<body bgcolor="#FFFFFF" link="#0000FF" vlink="#800080">
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<table border="0" cellpadding="7" cellspacing="0" width="100%">
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<tr>
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<td valign="top" width="300">
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<h3><img src="../../../c++boost.gif" alt="C++ Boost" width="277" height="86"></h3>
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</td>
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<td valign="top">
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<h1 align="center">Boost.Threads</h1>
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<h2 align="center">basic_trylock</h2>
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</td>
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</tr>
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</table>
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<hr>
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<p>This template class defines a <a href="lock_concept.html">lock type</a> that allows
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the program to attempt to lock the associated <a href="mutex_concept.html">mutex model</a>
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with out blocking. The <a href="mutex.html">try_mutex</a>, <a href="mutex.html">timed_mutex</a>,
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<a href="recursive_mutex.html">recursive_try_mutex</a> and
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<a href="recursive_mutex.html">recursive_timed_mutex</a> use this template to define their
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<tt>try_lock</tt> types.</p>
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<p>Like all the <b>Boost.Threads</b> <a href="lock_concept.html">lock models</a>, the
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<tt>basic_trylock</tt> is meant to be short lived and is not <a href="file:///c:/boost/site/libs/thread/doc/definitions.html#Thread-safe">thread-safe</a>, so should not be
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shared between threads.</p>
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<h2>Header</h2>
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<pre>
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#include <a href="../../../boost/thread/xlock.hpp"><boost/thread/xlock.hpp></a>
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<i>This header is usually not included directly by programmers.</i>
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</pre>
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<h2>Public Interface</h2>
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<hr width="50%" align="left">
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<pre>
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template <typename M>
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class basic_trylock : private boost::noncopyable
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{
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public:
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typedef M mutex_type;
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explicit basic_trylock(M& mx);
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basic_trylock(M& mx, bool lock_it);
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~basic_trylock();
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void lock();
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bool try_lock();
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void unlock();
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operator const void*() const;
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};
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</pre>
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<hr width="50%" align="left">
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<h3>Constructors</h3>
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<pre>
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explicit basic_trylock(M& mx);
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</pre>
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<p>Constructs a <tt>basic_trylock</tt> and calls <tt>try_lock</tt>.</p>
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<pre>
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basic_trylock(M& mx, bool lock_it);
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</pre>
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<p>Constructs a <tt>basic_trylock</tt> and if <tt>lock_it</tt> is <tt>true</tt> then
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calls <tt>lock</tt>.
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<h3>Destructor</h3>
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<pre>
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~basic_trylock();
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</pre>
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<p>Destructs the <tt>basic_trylock</tt> and if locked calls <tt>unlock</tt>.</p>
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<h3>lock</h3>
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<pre>
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void lock();
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</pre>
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<p>Locks the associated <a href="mutex_concept.html">mutex model</a>. If the <tt>basic_trylock</tt>
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is already locked then a <a href="lock_error.html">lock_error</a> is thrown. Depending on the
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<a href="mutex_concept.html#LockingStrategies">locking strategy</a> of the
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<a href="mutex_concept.html">mutex model</a> if the calling thread already owns a lock through
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another <a href="lock_concept.html">lock model</a> this may cause a deadlock or for a
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<a href="lock_error.html">lock_error</a> to be thrown.</p>
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<h3>try_lock</h3>
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<pre>
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bool try_lock();
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</pre>
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<p>Attempts to lock the associated <a href="mutex_concept.html">mutex_model</a>. If the <tt>basic_trylock</tt>
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is already locked then a <a href="lock_error.html">lock_error</a> is thrown. If the
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<a href="mutex_concept.html">mutex model</a> is already locked by another thread this attempt fails
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immediately with out blocking and returns <tt>false</tt>.</p>
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<h3>unlock</h3>
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<pre>
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void unlock();
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</pre>
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<p>Unlocks the associated <a href="mutex_concept.html#Mutex">mutex model</a>. If the <tt>basic_trylock</tt>
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is not already locked then a <a href="lock_error.html">lock_error</a> is thrown.</p>
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<h3>const void* Conversion</h3>
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<pre>
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operator const void*() const;
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</pre>
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<p>Implicitly converts the lock to a value that can be used in boolean expressions to test if the
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lock is currently locked or not.</p>
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<h2>Example Usage</h2>
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<pre>
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#include <a href="../../../boost/thread/mutex.hpp"><boost/thread/mutex.hpp></a>
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#include <iostream>
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int main(int, char*[])
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{
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boost::mutex mutex;
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boost::mutex::try_lock lock(mutex);
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if (lock)
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std::cout << "locked" << std::endl;
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else
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std::cout << "unlocked" << std::endl;
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return 0;
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}
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</pre>
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<p>The output is:</p>
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<pre>
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locked
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</pre>
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<hr>
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<p><i>Copyright <a href="mailto:williamkempf@hotmail.com">William E. Kempf</a>
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2001 all rights reserved.</i></p>
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</body>
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</html>
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