347 lines
11 KiB
HTML
347 lines
11 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_lock()--Lock Mutexe</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_lock()--Lock Mutex</h2>
|
|
|
|
<div class="box" style="width: 60%;">
|
|
<br>
|
|
Syntax:
|
|
|
|
<pre>
|
|
#include <pthread.h>
|
|
int pthread_mutex_lock(pthread_mutex_t *mutex);
|
|
</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_lock</strong>() function acquires ownership of the
|
|
mutex specified. If the mutex currently is locked by another thread, the call
|
|
to <strong>pthread_mutex_lock</strong>() blocks until that thread relinquishes
|
|
ownership by a call to <strong>pthread_mutex_unlock</strong>().</p>
|
|
|
|
<p>If a signal is delivered to a thread while that thread is waiting for a
|
|
mutex, when the signal handler returns, the wait resumes. <strong>
|
|
pthread_mutex_lock</strong>() does not return <strong>EINTR</strong> like some
|
|
other blocking function calls.</p>
|
|
|
|
<p>Use the CL command WRKJOB, option 20, to help you debug mutex deadlocks.</p>
|
|
|
|
<p>Destroying a held mutex is a common way to serialize destruction of objects
|
|
that are protected by that mutex. This action is allowed. The call to <strong>
|
|
pthread_mutex_lock</strong>() may fail with the <strong>EDESTROYED</strong>
|
|
error if the mutex is destroyed by the thread that was currently holding
|
|
it.</p>
|
|
|
|
<p>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>() or <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 was statically initialized
|
|
using <strong>PTHREAD_MUTEX_INITIALIZER</strong> and was not yet locked causes 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. When
|
|
this number is exceeded, attempts to lock the mutex return the <strong>
|
|
ERECURSE</strong> error.</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
|
|
relocks 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 relocks
|
|
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.
|
|
The pthreads run-time simulates the deadlock that has occurred in your
|
|
application. When you are attempting to debug these deadlock scenarios, the CL
|
|
command WRKJOB, option 20 shows the thread as in a condition wait. Displaying
|
|
the call stack shows that the function
|
|
<strong>deadlockOnOrphanedMutex</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. The pthreads run-time simulates the deadlock that
|
|
has occurred in your application. When you are attempting to debug these
|
|
deadlock scenarios, the CL command WRKJOB, option 20, shows the thread as in a
|
|
condition wait. Displaying the call stack will show that the function <strong>
|
|
deadlockOnAlreadyHeldMutex</strong> is in the call stack.</p>
|
|
|
|
<p>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_lock</strong>() was successful.</dd>
|
|
|
|
<dt><strong>value</strong></dt>
|
|
|
|
<dd><strong>pthread_mutex_lock</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_lock</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>[EOWNERTERM]</em></dt>
|
|
|
|
<dd><p>A thread terminated the holding of the mutex, and the mutex is an ownerterm
|
|
mutex type.</p></dd>
|
|
|
|
<dt><em>[EDEADLK]</em></dt>
|
|
|
|
<dd><p></p>A thread attempted to relock an already held mutex, and the mutex is an
|
|
errorcheck mutex type. <a name="336837"></a><p></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_64.htm">pthread_mutex_trylock()</a>--Lock Mutex with No
|
|
Wait<br><br></li>
|
|
|
|
<li><a href="users_63.htm">pthread_mutex_timedlock_np()</a>--Lock Mutex with Time-Out<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>
|
|
#include <pthread.h>
|
|
#include <stdio.h>
|
|
#include "check.h"
|
|
/*
|
|
This example shows the corruption that can result if no
|
|
serialization is done and also shows the use of
|
|
pthread_mutex_lock(). Call it with no parameters
|
|
to use pthread_mutex_lock() to protect the critical section,
|
|
or 1 or more parameters to show data corruption that occurs
|
|
without locking.
|
|
*/
|
|
#define LOOPCONSTANT 100000
|
|
#define THREADS 10
|
|
|
|
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
|
|
int i,j,k,l;
|
|
int uselock=1;
|
|
|
|
void *threadfunc(void *parm)
|
|
{
|
|
int loop = 0;
|
|
int rc;
|
|
|
|
for (loop=0; loop<LOOPCONSTANT; ++loop) {
|
|
if (uselock) {
|
|
rc = pthread_mutex_lock(&mutex);
|
|
checkResults("pthread_mutex_lock()\n", rc);
|
|
}
|
|
++i; ++j; ++k; ++l;
|
|
if (uselock) {
|
|
rc = pthread_mutex_unlock(&mutex);
|
|
checkResults("pthread_mutex_unlock()\n", rc);
|
|
}
|
|
}
|
|
return NULL;
|
|
}
|
|
|
|
int main(int argc, char **argv)
|
|
{
|
|
pthread_t threadid[THREADS];
|
|
int rc=0;
|
|
|
|
int loop=0;
|
|
pthread_attr_t pta;
|
|
|
|
printf("Entering testcase\n");
|
|
printf("Give any number of parameters to show data corruption\n");
|
|
if (argc != 1) {
|
|
printf("A parameter was specified, no serialization is being done!\n");
|
|
uselock = 0;
|
|
}
|
|
|
|
pthread_attr_init(&pta);
|
|
pthread_attr_setdetachstate(&pta, PTHREAD_CREATE_JOINABLE);
|
|
|
|
printf("Creating %d threads\n", THREADS);
|
|
for (loop=0; loop<THREADS; ++loop) {
|
|
rc = pthread_create(&threadid[loop], &pta, threadfunc, NULL);
|
|
checkResults("pthread_create()\n", rc);
|
|
}
|
|
|
|
printf("Wait for results\n");
|
|
for (loop=0; loop<THREADS; ++loop) {
|
|
rc = pthread_join(threadid[loop], NULL);
|
|
checkResults("pthread_join()\n", rc);
|
|
}
|
|
|
|
printf("Cleanup and show results\n");
|
|
pthread_attr_destroy(&pta);
|
|
pthread_mutex_destroy(&mutex);
|
|
|
|
printf("\nUsing %d threads and LOOPCONSTANT = %d\n",
|
|
THREADS, LOOPCONSTANT);
|
|
printf("Values are: (should be %d)\n", THREADS * LOOPCONSTANT);
|
|
printf(" ==>%d, %d, %d, %d\n", i, j, k, l);
|
|
|
|
printf("Main completed\n");
|
|
return 0;
|
|
}
|
|
</pre>
|
|
|
|
<p><strong>Output:</strong></p>
|
|
|
|
<pre>
|
|
Entering testcase
|
|
Give any number of parameters to show data corruption
|
|
Creating 10 threads
|
|
Wait for results
|
|
Cleanup and show results
|
|
|
|
Using 10 threads and LOOPCONSTANT = 100000
|
|
Values are: (should be 1000000)
|
|
==>1000000, 1000000, 1000000, 1000000
|
|
Main completed
|
|
</pre>
|
|
|
|
<br>
|
|
<p><strong>Output:</strong></p>
|
|
|
|
<a name="336938"></a>
|
|
|
|
<h3>(data corruption without locking example)</h3>
|
|
|
|
<pre>
|
|
Entering testcase
|
|
Give any number of parameters to show data corruption
|
|
A parameter was specified, no serialization is being done!
|
|
Creating 10 threads
|
|
Wait for results
|
|
Cleanup and show results
|
|
|
|
Using 10 threads and LOOPCONSTANT = 100000
|
|
Values are: (should be 1000000)
|
|
==>883380, 834630, 725131, 931883
|
|
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>
|
|
|