315 lines
10 KiB
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315 lines
10 KiB
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta name="Copyright" content="Copyright (c) 2006 by IBM Corporation">
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<title>pthread_mutex_timedlock_np()--Lock Mutex with Time-Out</title>
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<!-- Begin Header Records ========================================== -->
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<!-- NETMG2 SCRIPT A converted by B2H R4.1 (346) (CMS) by HOLTJM at -->
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<!-- RCHVMW2 on 29 Jan 1999 at 10:01:37 -->
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<!--File Edited November 2001 -->
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<!--End Header Records -->
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<link rel="stylesheet" type="text/css" href="../rzahg/ic.css">
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</head>
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<body>
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<!-- Java sync-link -->
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<script language="Javascript" src="../rzahg/synch.js" type="text/javascript">
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</script>
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<a name="Top_Of_Page"></a>
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<h2>pthread_mutex_timedlock_np()--Lock Mutex with Time-Out</h2>
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<div class="box" style="width: 70%;">
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<br>
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Syntax:
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<pre>
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#include <pthread.h>
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#include <time.h>
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int pthread_mutex_timedlock_np(pthread_mutex_t *mutex,
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const struct timespec *deltatime);
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</pre>
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Service Program Name: QP0WPTHR<br>
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<!-- iddvc RMBR -->
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<br>
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Default Public Authority: *USE <br>
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<!-- iddvc RMBR -->
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<br>
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Threadsafe: Yes<br>
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<!-- iddvc RMBR -->
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<br>
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Signal Safe: Yes<br>
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<!-- iddvc RMBR -->
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<br>
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</div>
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<p>The <strong>pthread_mutex_timedlock_np</strong>() function acquires
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ownership of the <em>mutex</em> specified. If the mutex is currently locked by
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another thread, the call to <strong>pthread_mutex_timedlock_np</strong>() will
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block until the specified deltatime has elapsed or the holding thread
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relinquishes ownership by a call to <strong>pthread_mutex_unlock</strong>().</p>
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<p>Performing a <strong>pthread_mutex_timedlock_np</strong>() wait for a mutex
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has different semantics related to signal handling than the <strong>
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pthread_mutex_lock</strong>() function. If a signal is delivered to a thread
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while that thread is performing a timed wait for a mutex, the signal is held
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pending until either the mutex is acquired or the time-out occurs. At that time
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the signal handler will run, when the signal handler returns, <strong>
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pthread_mutex_timedlock_np</strong>() will return the results of the timed mutex
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wait.</p>
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<p>Use the CL command WRKJOB, option 20 for a screen that will aid in debugging
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mutex deadlocks.</p>
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<p>Destroying a held mutex is a common way to serialize destruction of objects
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that are protected by that mutex, and is allowed. The call to <strong>
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pthread_mutex_timedlock_np</strong>() may fail with the <strong>
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EDESTROYED</strong> error if the mutex is destroyed by the thread that was
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currently holding it.</p>
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<p>Note that mutex initialization using the <strong>
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PTHREAD_MUTEX_INITIALIZER</strong> does not immediately initialize the mutex.
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Instead, on first use, <strong>pthread_mutex_timedlock_np</strong>(), <strong>
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pthread_mutex_lock</strong>() or <strong>pthread_mutex_trylock</strong>()
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branches into a slow path and causes the initialization of the mutex. Because a
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mutex is not just a simple memory object, and requires that some resources be
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allocated by the system, an attempt to call <strong>
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pthread_mutex_destroy</strong>() or <strong>pthread_mutex_unlock</strong>() on
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a mutex that has was statically initialized using <strong>
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PTHREAD_MUTEX_INITIALIZER</strong> and was not yet locked will result in an
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<strong>EINVAL</strong> error.</p>
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<p>A pthread mutex is a structure of type pthread_mutex_t that implement a
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behavior based on the Pthread mutexes. An MI mutex is a structure built into
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the machine that implement a similar sort of serialization construct.</p>
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<p>The maximum number of recursive locks by the owning thread is 32,767. After
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which, attempts to lock the mutex will return the <strong>ERECURSE</strong>
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error.</p>
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<p><strong>Note:</strong> This function is not portable</p>
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<br>
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<h3>Mutex Types</h3>
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<p>A normal mutex cannot be locked repeatedly by the owner. Attempts by a
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thread to relock an already held mutex, or to lock a mutex that was held by
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another thread when that thread terminated result in a deadlock condition.</p>
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<p>A recursive mutex can be locked repeatedly by the owner. The mutex does not
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become unlocked until the owner has called <strong>
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pthread_mutex_unlock</strong>() for each successful lock request that it has
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outstanding on the mutex.</p>
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<p>An errorcheck mutex checks for deadlock conditions that occur when a thread
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re-locks an already held mutex. If a thread attempts to relock a mutex that it
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already holds, the lock request fails with the <strong>EDEADLK</strong>
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error.</p>
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<p>An ownerterm mutex is an i5/OS extension to the errorcheck mutex type. An
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ownerterm mutex checks for deadlock conditions that occur when a thread
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re-locks an already held mutex. If a thread attempts to relock a mutex that it
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already holds, the lock request fails with the <strong>EDEADLK</strong> error.
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An ownerterm mutex also checks for deadlock conditions that occur when a thread
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attempts to lock a mutex that was held by another thread when that thread
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terminated (an orphaned mutex). If a thread attempts to lock an orphaned mutex,
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the lock request fails with the <strong>EOWNERTERM</strong> error.</p>
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<p>When a thread terminates while holding a mutex lock on a normal or errorcheck
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mutex, other threads that wait for that mutex will block forever, or until the
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specified deltatime has elapsed. The pthreads
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run-time simulates the deadlock that has occurred in your application. When
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attempting to debug these deadlock scenarios, the CL command WRKJOB, option 20
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will show the thread as in a condition wait. Displaying the call stack will
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show that the function <strong>deadlockedOnOrphanedMutex</strong> or <strong>
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timedDeadlockOnOrphanedMutex</strong> is in the
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call stack.</p>
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<p>When a thread attempts to acquire a normal mutex that it already holds, the
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thread will block forever, or until the specified deltatime has elapsed.
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The pthreads run-time simulates the deadlock that
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has occurred in your application. When attempting to debug these deadlock
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scenarios, the CL command WRKJOB, option 20 will show the thread as in a
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condition wait. Displaying the call stack will show that the function <strong>
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deadlockOnAlreadyHeldMutex</strong> or <strong>
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timedDeadlockOnAlreadyHeldMutex</strong> is in the call stack.</p>
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<p>In order to change these behaviors, use an errorcheck or ownerterm mutex
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type.</p>
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<br>
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<h3>Authorities and Locks</h3>
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<p>None.</p>
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<br>
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<h3>Parameters</h3>
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<dl>
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<dt><strong>mutex</strong></dt>
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<dd>(Input) The address of the mutex to lock</dd>
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</dl>
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<br>
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<h3>Return Value</h3>
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<dl>
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<dt><strong>0</strong></dt>
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<dd><strong>pthread_mutex_timedlock_np</strong>() was successful.</dd>
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<dt><strong>value</strong></dt>
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<dd><strong>pthread_mutex_timedlock_np</strong>() was not successful. <em>
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value</em> is set to indicate the error condition.</dd>
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</dl>
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<br>
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<h3>Error Conditions</h3>
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<p>If <strong>pthread_mutex_timedlock_np</strong>() was not successful, the
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error condition returned usually indicates one of the following errors. Under
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some conditions, the value returned could indicate an error other than those
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listed here.</p>
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<dl>
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<dt><em>[EINVAL]</em></dt>
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<dd><p>The value specified for the argument is not correct.</p></dd>
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<dt><em>[EDESTROYED]</em></dt>
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<dd><p>While waiting for the mutex lock to be satisfied, the mutex was
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destroyed.</p></dd>
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<dt><em>[EBUSY]</em></dt>
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<dd><p>The attempt to lock the mutex timed out because the mutex was already
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locked.</p></dd>
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<dt><em>[EOWNERTERM]</em></dt>
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<dd><p>A thread terminated holding the mutex, and the mutex is an ownerterm mutex
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type.</p></dd>
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<dt><em>[EDEADLK]</em></dt>
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<dd><p>A thread attempted to relock an already held mutex, and the mutex is an
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errorcheck mutex type.</p></dd>
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<dt><em>[ERECURSE]</em></dt>
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<dd><p>The recursive mutex cannot be recursively locked again.</p></dd>
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</dl>
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<br>
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<h3>Related Information</h3>
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<ul>
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<li>The <<strong>pthread.h</strong>> header file. See <a href=
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"rzah4hed.htm">Header files for Pthread functions</a>.<br><br></li>
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<li><a href="users_60.htm">pthread_mutex_destroy()</a>--Destroy Mutex<br><br></li>
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<li><a href="users_61.htm">pthread_mutex_init()</a>--Initialize Mutex<br><br></li>
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<li><a href="users_62.htm">pthread_mutex_lock()</a>--Lock Mutex<br><br></li>
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<li><a href="users_64.htm">pthread_mutex_trylock()</a>--Lock Mutex with No
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Wait<br><br></li>
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<li><a href="users_65.htm">pthread_mutex_unlock()</a>--Unlock Mutex</li>
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</ul>
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<br>
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<h3>Example</h3>
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<p>See <a href="../apiref/aboutapis.htm#codedisclaimer">Code disclaimer information</a>
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for information pertaining to code examples.</p>
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<pre>
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#define _MULTI_THREADED
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#include <pthread.h>
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#include <stdio.h>
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#include "check.h"
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pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
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void *threadFunc(void *parm)
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{
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int rc;
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int i;
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struct timespec deltatime;
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deltatime.tv_sec = 5;
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deltatime.tv_nsec = 0;
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printf("Timed lock the mutex from a secondary thread\n");
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rc = pthread_mutex_timedlock_np(&mutex, &deltatime);
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if (rc != EBUSY) {
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printf("Got an incorrect return code from pthread_mutex_timedlock_np\n");
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}
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printf("Thread mutex timeout\n");
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return 0;
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}
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int main(int argc, char **argv)
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{
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int rc=0;
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pthread_t thread;
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printf("Enter Testcase - %s\n", argv[0]);
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printf("Acquire the mutex in the initial thread\n");
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rc = pthread_mutex_lock(&mutex);
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checkResults("pthread_mutex_lock()\n", rc),
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printf("Create a thread\n");
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rc = pthread_create(&thread, NULL, threadFunc, NULL);
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checkResults("pthread_create()\n", rc);
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printf("Join to the thread\n");
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rc = pthread_join(thread, NULL);
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checkResults("pthread_join()\n", rc);
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printf("Destroy mutex\n");
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pthread_mutex_destroy(&mutex);
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printf("Main completed\n");
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return 0;
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}
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</pre>
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<p><strong>Output:</strong></p>
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<pre>
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Enter Testcase - QP0WTEST/TPMTXTIM0
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Acquire the mutex in the initial thread
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Create a thread
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Join to the thread
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Timed lock the mutex from a secondary thread
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Thread mutex timeout
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Destroy mutex
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Main completed
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</pre>
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<hr>
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API introduced: V4R3
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<hr>
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<center>
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<table cellpadding="2" cellspacing="2">
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<tr align="center">
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<td valign="middle" align="center"><a href="#Top_Of_Page">Top</a> | <a href=
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"rzah4mst.htm">Pthread APIs</a> | <a href="aplist.htm">APIs by
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category</a></td>
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</tr>
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</table>
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</center>
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</body>
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</html>
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