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<html><!-- #BeginTemplate "/Templates/tmpl.dwt" --><head><!-- #BeginEditable "doctitle" --> <title>PTypes: multithreading: utils</title><!-- #EndEditable --> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link rel="stylesheet" href="styles.css"></head><body bgcolor="#FFFFFF" leftmargin="40" marginwidth="40"><p><a href="../index.html"><img src="title-1.7.gif" width="213" height="34" alt="C++ Portable Types Library (PTypes) Version 1.7" border="0"></a> <hr noshade><!-- #BeginEditable "body" --> <p class="hpath"><a href="index.html">Top</a>: <a href="async.html">Multithreading</a>: Utilities</p><blockquote> <pre class="lang">#include <pasync.h>int pexchange(int* target, int value);void* pexchange(void** target, void* value);int pincrement(int* target);int pdecrement(int* target);template <class T> inline T* tpexchange(T** target, T* value);void psleep(unsigned milliseconds);pthread_id_t pthrself();bool pthrequal(pthread_id_t id);</pre></blockquote><p>The atomic functions <span class="lang">pexchange()</span>, <span class="lang">pincrement()</span> and <span class="lang">pdecrement()</span> can be used in place of mutex locking in some simple situations. A typical usage of <span class="lang">pexchange()</span> in a multithreaded environment could be, for example, freeing a dynamic object and assigning NULL to the pointer <b>atomically</b> to prevent concurrent threads from freeing the same object more than once.</p><p>It is sometimes necessary to increment or decrement some shared counter and atomically compare it with some value. For example, you have a shared resource and you keep track of its usage by maintaining a reference counter. When this counter reaches 0 you want to free the shared resource. To avoid conflicts between concurrent threads you need to decrement the counter and atomically compare it with 0. In this situation you can use <span class="lang">pdecrement()</span> instead of time-consuming mutex locking. (For additional notes, see <a href="portability.html">Portability and performance issues</a>.)</p><p><span class="def">int pexchange(int* target, int value)</span> -- atomically exchanges two int values.</p><p><span class="def">void* pexchange(void** target, void* value)</span> -- atomically exchanges two pointers.</p><p><span class="def">int pincrement(int* target)</span> -- atomically increments the value of <span class="lang">*target</span> and returns the new value.</p><p><span class="def">int pdecrement(int* target)</span> -- atomically decrements the value of <span class="lang">*target</span> and returns the new value.</p><p><span class="def">template <class T> T* tpexchange(T** target, T* value)</span> -- is equivalent to <span class="lang">pexchange()</span> that adds compile-time type checking. Use this template to check the correspondence of pointer types of <span class="lang">target</span> and the returning value.</p><p><span class="def">void psleep(unsigned milliseconds)</span> -- suspends execution for the specified amount of time in milliseconds.</p><p><span class="def">pthread_id_t pthrself()</span> -- returns the thread ID of the calling thread.</p><p><span class="def">bool pthrequal(pthread_id_t id)</span> -- checks whether the calling thread has the given thread <span class="lang">id</span>.</p><p class="seealso">See also: <a href="async.semaphore.html">semaphore</a>, <a href="async.examples.html">mutex</a>, <a href="async.thread.html">thread</a></p><!-- #EndEditable --> <hr size="1"><a href="../index.html" class="ns">PTypes home</a></body><!-- #EndTemplate --></html>?? 快捷鍵說明
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