friedkiwi/ibm-information-center
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity
14ed2849c6
ibm-information-center/dist/eclipse/plugins/i5OS.ic.apis_5.4.0.1/users_82.htm

610 lines
21 KiB
HTML
Raw Blame History

<!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_rwlockattr_getpshared()--Get Pshared Read/Write Lock
Attribute</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_rwlockattr_getpshared()--Get Pshared Read/Write Lock Attribute</h2>
<div class="box" style="width: 70%;">
<br>
&nbsp;&nbsp;Syntax:
<pre>
#include &lt;pthread.h&gt;
int pthread_rwlockattr_getpshared(const pthread_rwlockattr_t *attr,
int *pshared);
</pre>
<br>
&nbsp;&nbsp;Service Program Name: QP0WPTHR<br>
<!-- iddvc RMBR -->
<br>
&nbsp;&nbsp;Default Public Authority: *USE <br>
<!-- iddvc RMBR -->
<br>
&nbsp;&nbsp;Threadsafe: Yes<br>
<!-- iddvc RMBR -->
<br>
&nbsp;&nbsp;Signal Safe: Yes<br>
<!-- iddvc RMBR -->
<br>
</div>
<p>The <strong>pthread_rwlockattr_getpshared</strong>() function retrieves the
current setting of the process shared attribute from the read/write lock
attributes object. The process shared attribute indicates whether the
read/write lock that is created using the read/write lock attributes object can
be shared between threads in separate processes
(<strong>PTHREAD_PROCESS_SHARED</strong>) or shared only between threads within
the same process (<strong>PTHREAD_PROCESS_PRIVATE</strong>).</p>
<p>Even if the read/write lock in storage is accessible from two separate
processes, it cannot be used from both processes unless the process shared
attribute is <strong>PTHREAD_PROCESS_SHARED</strong>.</p>
<p>The default pshared attribute for read/write lock attributes objects is
<strong>PTHREAD_PROCESS_PRIVATE</strong>.</p>
<br>
<h3>Authorities and Locks</h3>
<p>None.</p>
<br>
<h3>Parameters</h3>
<dl>
<dt><strong>attr</strong></dt>
<dd>(Input) Address of the variable that contains the read/write lock
attributes object</dd>
<dt><strong>pshared</strong></dt>
<dd>(Output) Address of the variable to contain the pshared attribute
result</dd>
</dl>
<br>
<h3>Return Value</h3>
<dl>
<dt><strong>0</strong></dt>
<dd><strong>pthread_rwlockattr_getpshared</strong>() was successful.</dd>
<dt><strong>value</strong></dt>
<dd><strong>pthread_rwlockattr_getpshared</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_rwlockattr_getpshared</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>
</dl>
<br>
<h3>Related Information</h3>
<ul>
<li>The &lt;<strong>pthread.h</strong>&gt; header file. See <a href=
"rzah4hed.htm">Header files for Pthread functions</a>.<br><br></li>
<li><a href="users_83.htm">pthread_rwlockattr_init()</a>--Initialize Read/Write
Lock Attribute<br><br></li>
<li><a href="users_84.htm">pthread_rwlockattr_setpshared()</a>--Set Pshared
Read/Write Lock Attribute<br><br></li>
<li><a href="users_86.htm">pthread_rwlock_init()</a>--Initialize Read/Write
Lock</li>
</ul>
<br>
<h3><a name="371750">Example</a></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 &lt;pthread.h&gt;
#include &lt;stdio.h&gt;
#include &lt;spawn.h&gt;
#include &lt;sys/wait.h&gt;
#include &lt;unistd.h&gt;
#include &lt;sys/shm.h&gt;
#include "check.h"
typedef struct {
int protectedResource;
pthread_rwlock_t rwlock;
} shared_data_t;
extern char **environ;
shared_data_t *sharedMem=NULL;
pid_t childPid=0;
int childStatus=-99;
int shmid=0;
/* Change this path to be the path to where you create this example program */
#define MYPATH "/QSYS.LIB/QP0WTEST.LIB/TPRWLSH0.PGM"
#define NTHREADSTHISJOB 2
#define NTHREADSTOTAL 4
void parentSetup(void);
void childSetup(void);
void parentCleanup(void);
void childCleanup(void);
void *childReaderThreadFunc(void *parm)
{
int rc;
int retries = 5;
while (retries--) {
rc = pthread_rwlock_rdlock(&amp;sharedMem-&gt;rwlock);
checkResults("pthread_rwlock_rdlock()\n", rc);
/* Under protection of the shared read lock, read the resource */
printf("CHILD READER - current protectedResource = %d\n",
sharedMem-&gt;protectedResource);
sleep(1);
printf("CHILD READER - unlock\n");
rc = pthread_rwlock_unlock(&amp;sharedMem-&gt;rwlock);
checkResults("pthread_rwlock_unlock()\n", rc);
}
return NULL;
}
void *parentWriterThreadFunc(void *parm)
{
int rc;
rc = pthread_rwlock_wrlock(&amp;sharedMem-&gt;rwlock);
checkResults("pthread_rwlock_rdlock()\n", rc);
/* Under protection of the exclusive write lock, write the resource */
++sharedMem-&gt;protectedResource;
printf("PARENT WRITER - current protectedResource = %d\n",
sharedMem-&gt;protectedResource);
sleep(5);
printf("PARENT WRITER - unlock\n");
rc = pthread_rwlock_unlock(&amp;sharedMem-&gt;rwlock);
checkResults("pthread_rwlock_unlock()\n", rc);
return NULL;
}
int main(int argc, char **argv)
{
int rc=0;
int i;
pthread_t threadid[NTHREADSTHISJOB];
int parentJob=0;
void *status=NULL;
/* If we run this from the QSHELL interpreter on the system, we want */
/* it to be line buffered even if we run it in batch so the output between*/
/* parent and child is intermixed. */
setvbuf(stdout,NULL,_IOLBF,4096);
/* Determine if we are running in the parent or child */
if (argc != 1 &amp;&amp; argc != 2) {
printf("Incorrect usage\n");
printf("Pass no parameters to run as the parent testcase\n");
printf("Pass one parameter `ASCHILD' to run as the child testcase\n");
exit(1);
}
if (argc == 1) {
parentJob = 1;
}
else {
if (strcmp(argv[1], "ASCHILD")) {
printf("Incorrect usage\n");
printf("Pass no parameters to run as the parent testcase\n");
printf("Pass one parameter `ASCHILD' to run as the child testcase\n");
exit(1);
}
parentJob = 0;
}
/* PARENT *****************************************************************/
if (parentJob) {
printf("PARENT - Enter Testcase - %s\n", argv[0]);
parentSetup();
printf("PARENT - Create %d threads\n", NTHREADSTHISJOB);
for (i=0; i&lt;NTHREADSTHISJOB; ++i) {
rc = pthread_create(&amp;threadid[i], NULL, parentWriterThreadFunc, NULL);
checkResults("pthread_create()\n", rc);
}
for (i=0; i&lt;NTHREADSTHISJOB; ++i) {
rc = pthread_join(threadid[i], NULL);
checkResults("pthread_create()\n", rc);
if (status != NULL) {
printf("PARENT - Got a bad status from a thread, "
"%.8x %.8x %.8x %.8x\n", status);
exit(1);
}
}
parentCleanup();
printf("PARENT - Main completed\n");
exit(0);
}
/* CHILD *****************************************************************/
{
printf("CHILD - Enter Testcase - %s\n", argv[0]);
childSetup();
printf("CHILD - Create %d threads\n", NTHREADSTHISJOB);
for (i=0; i&lt;NTHREADSTHISJOB; ++i) {
rc = pthread_create(&amp;threadid[i], NULL, childReaderThreadFunc, NULL);
checkResults("pthread_create()\n", rc);
}
/* The parent will wake up all of these threads using the */
/* pshared condition variable. We will just join to them... */
printf("CHILD - Joining to all threads\n");
for (i=0; i&lt;NTHREADSTHISJOB; ++i) {
rc = pthread_join(threadid[i], &amp;status);
checkResults("pthread_join()\n", rc);
if (status != NULL) {
printf("CHILD - Got a bad status from a thread, "
"%.8x %.8x %.8x %.8x\n", status);
exit(1);
}
}
/* After all the threads are awake, the parent will destroy */
/* the read/write lock. Do not use it anymore */
childCleanup();
printf("CHILD - Main completed\n");
}
return 0;
}
/***************************************************************/
/* This function initializes the shared memory for the job, */
/* sets up the environment variable indicating where the shared*/
/* memory is, and spawns the child job. */
/* */
/* It creates and initializes the shared memory segment, and */
/* It initializes the following global variables in this */
/* job. */
/* sharedMem */
/* childPid */
/* shmid */
/* */
/* If any of this setup/initialization fails, it will exit(1) */
/* and terminate the test. */
/* */
/***************************************************************/
void parentSetup(void)
{
int rc;
/***************************************************************/
/* Create shared memory for shared_data_t above */
/* attach the shared memory */
/* set the static/global sharedMem pointer to it */
/***************************************************************/
printf("PARENT - Create the shared memory segment\n");
rc = shmget(IPC_PRIVATE, sizeof(shared_data_t), 0666);
if (rc == -1) {
printf("PARENT - Failed to create a shared memory segment\n");
exit(1);
}
shmid = rc;
printf("PARENT - Attach the shared memory\n");
sharedMem = shmat(shmid, NULL, 0);
if (sharedMem == NULL) {
shmctl(shmid, IPC_RMID, NULL);
printf("PARENT - Failed to attach shared memory\n");
exit(1);
}
/***************************************************************/
/* Initialize the read/write lock and other shared memory data */
/***************************************************************/
{
pthread_rwlockattr_t rwlattr;
printf("PARENT - Init shared memory and read/write lock\n");
memset(sharedMem, 0, sizeof(shared_data_t));
/* Process Shared Read/Write lock */
rc = pthread_rwlockattr_init(&amp;rwlattr);
checkResults("pthread_rwlockattr_init()\n", rc);
rc = pthread_rwlockattr_setpshared(&amp;rwlattr, PTHREAD_PROCESS_SHARED);
checkResults("pthread_rwlockattr_setpshared()\n", rc);
rc = pthread_rwlock_init(&amp;sharedMem-&gt;rwlock, &amp;rwlattr);
checkResults("pthread_rwlock_init()\n", rc);
}
/**************************************************************/
/* Set and environment variable so that the child can inherit */
/* it and know the shared memory ID */
/**************************************************************/
{
char shmIdEnvVar[128];
sprintf(shmIdEnvVar, "TPRWLSH0_SHMID=%d\n", shmid);
rc = putenv(shmIdEnvVar);
if (rc) {
printf("PARENT - Failed to store env var %s, errno=%d\n",
shmIdEnvVar, errno);
exit(1);
}
printf("PARENT - Stored shared memory id of %d\n", shmid);
}
/**************************************************/
/* Spawn the child job */
/**************************************************/
{
inheritance_t in;
char *av[3] = {NULL, NULL, NULL};
/* Allow thread creation in the spawned child */
memset(&amp;in, 0, sizeof(in));
in.flags = SPAWN_SETTHREAD_NP;
/* Set up the arguments to pass to spawn based on the */
/* arguments passed in */
av[0] = MYPATH;
av[1] = "ASCHILD";
av[2] = NULL;
/* Spawn the child that was specified, inheriting all */
/* of the environment variables. */
childPid = spawn(MYPATH, 0, NULL, &amp;in, av, environ);
if (childPid == -1) {
/* spawn failure */
printf("PARENT - spawn() failed, errno=%d\n", errno);
exit(1);
}
printf("PARENT - spawn() success, [PID=%d]\n", childPid);
}
return;
}
/***************************************************************/
/* This function attaches the shared memory for the child job, */
/* It uses the environment variable indicating where the shared*/
/* memory is. */
/* */
/* If any of this setup/initialization fails, it will exit(1) */
/* and terminate the test. */
/* */
/* It initializes the following global variables: */
/* sharedMem */
/* shmid */
/***************************************************************/
void childSetup(void)
{
int rc;
printf("CHILD - Child setup\n");
/**************************************************************/
/* Set and environment variable so that the child can inherit */
/* it and know the shared memory ID */
/**************************************************************/
{
char *shmIdEnvVar;
shmIdEnvVar = getenv("TPRWLSH0_SHMID");
if (shmIdEnvVar == NULL) {
printf("CHILD - Failed to get env var \"TPRWLSH0_SHMID\", errno=%d\n",
errno);
exit(1);
}
shmid = atoi(shmIdEnvVar);
printf("CHILD - Got shared memory id of %d\n", shmid);
}
/***************************************************************/
/* Create shared memory for shared_data_t above */
/* attach the shared memory */
/* set the static/global sharedMem pointer to it */
/***************************************************************/
printf("CHILD - Attach the shared memory\n");
sharedMem = shmat(shmid, NULL, 0);
if (sharedMem == NULL) {
shmctl(shmid, IPC_RMID, NULL);
printf("CHILD - Failed to attach shared memory\n");
exit(1);
}
return;
}
/***************************************************************/
/* wait for child to complete and get return code. */
/* Destroy read/write lock in shared memory */
/* detach and remove shared memory */
/* set the child's return code in global storage */
/* */
/* If this function fails, it will call exit(1) */
/* */
/* This function sets the following global variables: */
/* sharedMem */
/* childStatus */
/* shmid */
/***************************************************************/
void parentCleanup(void)
{
int status=0;
int rc;
int waitedPid=0;
/* Even though there is no thread left in the child using the */
/* contents of the shared memory, before we destroy the */
/* read/write lock in that shared memory, we will wait for the */
/* child job to complete, we know for 100% certainty that no */
/* threads in the child are using it then, because the child */
/* is terminated. */
printf("PARENT - Parent cleanup\n");
/* Wait for the child to complete */
waitedPid = waitpid(childPid,&amp;status,0);
if (rc == -1) {
printf("PARENT - waitpid failed, errno=%d\n", errno);
exit(1);
}
childStatus = status;
/* Cleanup resources */
rc = pthread_rwlock_destroy(&amp;sharedMem-&gt;rwlock);
checkResults("pthread_rwlock_destroy()\n", rc);
/* Detach/Remove shared memory */
rc = shmdt(sharedMem);
if (rc) {
printf("PARENT - Failed to detach shared memory, errno=%d\n", errno);
exit(1);
}
rc = shmctl(shmid, IPC_RMID, NULL);
if (rc) {
printf("PARENT - Failed to remove shared memory id=%d, errno=%d\n",
shmid, errno);
exit(1);
}
shmid = 0;
return;
}
/***************************************************************/
/* Detach the shared memory */
/* At this point, there is no serialization, so the contents */
/* of the shared memory should not be used. */
/* */
/* If this function fails, it will call exit(1) */
/* */
/* This function sets the following global variables: */
/* sharedMem */
/***************************************************************/
void childCleanup(void)
{
int rc;
printf("CHILD - Child cleanup\n");
rc = shmdt(sharedMem);
sharedMem = NULL;
if (rc) {
printf("CHILD - Failed to detach shared memory, errno=%d\n", errno);
exit(1);
}
return;
}
</pre>
<p><strong>Output:</strong></p>
<p>This example was run under the i5/OS QShell Interpreter. In the QShell
Interpreter, a program gets descriptors 0, 1, 2 as the standard files, the
parent and child I/O is directed to the console. When run in the QShell
Interpreter, the output shows the intermixed output from both parent and child
processes, and gives a feeling for the time sequence of operations occurring in
each job.</p>
<p>The QShell interpreter allows you to run multithreaded programs as if they
were interactive. See the QShell documentation for a description of the
QIBM_MULTI_THREADED shell variable which allows you to start multithreaded
programs.</p>
<p>The QShell Interpreter is option 30 of Base i5/OS.</p>
<pre>
PARENT - Enter Testcase - QP0WTEST/TPRWLSH0
PARENT - Create the shared memory segment
PARENT - Attach the shared memory
PARENT - Init shared memory and read/write lock
PARENT - Stored shared memory id of 7
PARENT - spawn() success, [PID=584]
PARENT - Create 2 threads
PARENT WRITER - current protectedResource = 1
CHILD - Enter Testcase - QP0WTEST/TPRWLSH0
CHILD - Child setup
CHILD - Got shared memory id of 7
CHILD - Attach the shared memory
CHILD - Create 2 threads
CHILD - Joining to all threads
PARENT WRITER - unlock
PARENT WRITER - current protectedResource = 2
PARENT WRITER - unlock
CHILD READER - current protectedResource = 2
CHILD READER - current protectedResource = 2
PARENT - Parent cleanup
CHILD READER - unlock
CHILD READER - current protectedResource = 2
CHILD READER - unlock
CHILD READER - current protectedResource = 2
CHILD READER - unlock
CHILD READER - current protectedResource = 2
CHILD READER - unlock
CHILD READER - current protectedResource = 2
CHILD READER - unlock
CHILD READER - current protectedResource = 2
CHILD READER - unlock
CHILD READER - current protectedResource = 2
CHILD READER - unlock
CHILD READER - current protectedResource = 2
CHILD READER - unlock
CHILD READER - current protectedResource = 2
CHILD READER - unlock
CHILD READER - unlock
CHILD - Child cleanup
CHILD - Main completed
PARENT - Main completed
</pre>
<br>
<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>
Reference in New Issue View Git Blame Copy Permalink