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78 lines
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HTML
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<title>Mutexes and threads</title>
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<body id="rzahwmut-mutco"><a name="rzahwmut-mutco"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Mutexes and threads</h1>
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<div><p>A mutual exclusion (mutex) is used cooperatively between threads
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to ensure that only one of the cooperating threads is allowed to access the
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data or run certain application code at a time.</p>
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<div class="section"><p>The word mutex is shorthand for a primitive object that provides
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MUTual EXclusion between threads. For the purposes of this introduction, you
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can think of mutexes as similar to critical sections and monitors.</p>
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</div>
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<div class="section"><p>The mutex is typically logically associated with the data it protects
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by the application. For example, PAYROLL DATA has a PAYROLL MUTEX associated
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with it. The application code always locks the PAYROLL MUTEX before accessing
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the PAYROLL DATA. The mutex prevents access to the data by a thread only if
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that thread uses the mutex before accessing the data.</p>
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</div>
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<div class="section"><p>Create, lock, unlock, and destroy are operations typically performed
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on a mutex. Any thread that successfully locks the mutex is the owner until
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it unlocks the mutex. Any thread that attempts to lock the mutex waits until
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the owner unlocks the mutex. When the owner unlocks the mutex, control is
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returned to one waiting thread with that thread becoming the owner of the
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mutex. There can be only one owner of a mutex.</p>
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</div>
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<div class="section"><p>Mutex wait operations can be recursive. Recursive mutexes allow
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the owner to lock the mutex repeatedly. The owner of the mutex remains the
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same until the number of unlock requests is the same as the number of successful
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lock requests. Mutex waits can time out after a user specified amount of time
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or can return immediately if they cannot acquire the lock. For more information,
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see your API set documentation about mutex
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primitives available for your application.</p>
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</div>
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</div>
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<div>
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<ul class="ullinks">
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<li class="ulchildlink"><strong><a href="rzahwe18rx.htm">Example: Use mutexes in Pthread programs</a></strong><br />
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This example shows a Pthread program starting several threads that protect access to shared data with a mutual exclusion (mutex).</li>
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<li class="ulchildlink"><strong><a href="rzahwex4rx.htm">Example: Use mutexes in Java</a></strong><br />
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This example shows a Java™ program creating a critical section
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of code. In Java™, any object or array can function similarly to
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a mutual exclusion (mutex) using the synchronized keyword on a block of code
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or a method.</li>
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</ul>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzahwsynco.htm" title="When you create code that is threadsafe but still benefits from sharing data or resources between threads, the most important aspect of programming becomes the ability to synchronize threads.">Synchronization techniques among threads</a></div>
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