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