📄 async.rwlock.html
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<html><!-- #BeginTemplate "/Templates/tmpl.dwt" --><!-- DW6 --><head><!-- #BeginEditable "doctitle" --> <title>PTypes: multithreading: rwlock</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-20.png" width="253" height="39" alt="C++ Portable Types Library (PTypes) Version 2.0" border="0"></a> <hr size="1" noshade><!-- #BeginEditable "body" --> <p class="hpath"><a href="index.html">Top</a>: <a href="async.html">Multithreading</a>: rwlock</p><blockquote> <pre class="lang">#include <pasync.h>class rwlock { rwlock(); void rdlock(); void wrlock(); void unlock();}class scoperead { scoperead(rwlock&); ~scoperead();}class scopewrite { scopewrite(rwlock&); ~scopewrite();}</pre></blockquote><p><span class="lang">Rwlock</span> (read/write lock) is a variation of <span class="lang">mutex</span> with a possibility to control critical sections more efficiently. Unlike the simple mutex, <span class="lang">rwlock</span> allows multiple <i>reader</i> threads to enter the critical section, and only one <i>writer</i> thread at a time. Reading and writing in this context means access to a resource or compound data shared between threads. Reader threads must lock the critical section with <span class="lang">rdlock()</span> and the writers must lock it with <span class="lang">wrlock()</span>. Both leave the critical section with <span class="lang">unlock()</span>.</p><p>This class incorporates POSIX rwlock interface on UNIX and library's own implementation on Windows and MacOS X. When using the <span class="lang">rwlock</span> class on Linux, you need to define a symbol <span class="lang">_GNU_SOURCE</span> either in the command line, or anywhere in your source before including any system headers.</p><p>Analogously to <span class="lang">scopelock</span> (see <a href="async.mutex.html">mutex</a>), <span class="lang">scoperead</span> and <span class="lang">scopewrite</span> are fully-inline'd utility classes provided for exception-safe locking of operator blocks.</p><p>Please, see <a href="portability.html">Portability and performance issues</a> for additional notes on rwlock implementation. </p><p><span class="def">rwlock::rwlock()</span> creates a <span class="lang">rwlock</span> object.</p><p><span class="def">void rwlock::rdlock()</span> locks the object for reading. Multiple threads can enter the critical section through <span class="lang">rdlock()</span>, however, if the object is already locked for writing, all reader threads wait until the writer leaves the critical section.</p><p><span class="def">void rwlock::wrlock()</span> locks the object for writing. If there are readers inside the critical section, the writer waits until all threads leave and unlock the object. Only one writer at a time can enter the critical section.</p><p><span class="def">void rwlock::unlock()</span> unlocks the object. Both readers and writers must use this method when leaving the critical section.</p><p><span class="def">scoperead::scoperead(rwlock& rw)</span> creates a <span class="lang">scoperead</span> object and calls <span class="lang">rdlock()</span> for the object <span class="lang">rw</span>.</p><p><span class="def">scoperead::~scoperead()</span> calls <span class="lang">unlock()</span> for the <span class="lang">rwlock</span> object specified during construction and destroys the <span class="lang">scoperead</span> object.</p><p><span class="def">scopewrite::scopewrite(rwlock& rw)</span> creates a <span class="def">scopewrite</span> object and calls <span class="lang">wrlock()</span> for the object <span class="lang">rw</span>.</p><p><span class="def">scopewrite::~scopewrite()</span> calls <span class="lang">unlock()</span> for the <span class="lang">rwlock</span> object specified during construction and destroys the <span class="def">scopewrite</span> object.</p><p class="seealso">See also: <a href="async.thread.html">thread</a>, <a href="async.mutex.html">mutex</a>, <a href="async.trigger.html">trigger</a>, <a href="async.semaphore.html">semaphore</a>, <a href="async.examples.html">Examples</a></p><!-- #EndEditable --><hr size="1"><a href="../index.html" class="ns">PTypes home</a></body><!-- #EndTemplate --></html>⌨️ 快捷键说明
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