255 lines
6.5 KiB
HTML
255 lines
6.5 KiB
HTML
<!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_lock_global_np()--Lock Global Mutex</title>
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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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<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_lock_global_np()--Lock Global Mutex</h2>
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<div class="box" style="width: 50%;">
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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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int pthread_lock_global_np(void);
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</pre>
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Service Program Name: QP0WTCBH<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_lock_global_np</strong>() function locks a global mutex
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provided by the pthreads run-time. The global mutex is a recursive mutex with a
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name of "QP0W_GLOBAL_MTX". The global mutex is not currently used by the
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pthreads run-time to serialize access to any system resources, and is provided
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for application use only.</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>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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<p>None.</p>
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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_lock_global_np</strong>() was successful.</dd>
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<dt><strong>value</strong></dt>
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<dd><strong>pthread_lock_global_np</strong>() was not successful.
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<em>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_lock_global_np</strong>() was not successful, the error
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condition returned usually indicates one of the following errors. Under some
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conditions, the value returned could indicate an error other than those listed
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here.</p>
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<dl>
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<dt><em>[EINVAL]</em></dt>
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<dd>
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<p>The value specified for the argument is not correct.</p>
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</dd>
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<dt><em>[ERECURSE]</em></dt>
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<dd>
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<p>The recursive mutex cannot be recursively locked again.</p>
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</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_67.htm">pthread_unlock_global_np()--Unlock Global
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Mutex</a></li>
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</ul>
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<br>
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<h3><a name="307944">Example</a></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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#include <pthread.h>
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#include <stdio.h>
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#include "check.h"
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/*
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This example shows the corruption that can result if no
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serialization is done and also shows the use of
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pthread_lock_global_np(). Call this test with no parameters
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to use pthread_lock_gloabl_np() to protect the critical data,
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between more than one (possibly unrelated) functions.
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Use 1 or more parameters to skip locking and
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show data corruption that occurs without locking.
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*/
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#define LOOPCONSTANT 50000
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#define THREADS 10
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int i,j,k,l;
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int uselock=1;
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void secondFunction(void)
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{
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int rc;
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if (uselock) {
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rc = pthread_lock_global_np();
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checkResults("pthread_lock_global_np()\n", rc);
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}
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--i; --j; --k; --l;
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if (uselock) {
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rc = pthread_unlock_global_np();
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checkResults("pthread_unlock_global_np()\n", rc);
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}
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}
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void *threadfunc(void *parm)
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{
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int loop = 0;
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int rc;
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for (loop=0; loop<LOOPCONSTANT; ++loop) {
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if (uselock) {
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rc = pthread_lock_global_np();
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checkResults("pthread_lock_global_np()\n", rc);
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}
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++i; ++j; ++k; ++l;
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secondFunction();
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++i; ++j; ++k; ++l;
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if (uselock) {
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rc = pthread_unlock_global_np();
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checkResults("pthread_unlock_global_np()\n", rc);
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}
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}
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return NULL;
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}
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int main(int argc, char **argv)
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{
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pthread_t threadid[THREADS];
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int rc=0;
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int loop=0;
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printf("Enter Testcase - %s\n", argv[0]);
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printf("Give any number of parameters to show data corruption\n");
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if (argc != 1) {
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printf("A parameter was specified, no serialization is being done!\n");
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uselock = 0;
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}
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if (uselock) {
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rc = pthread_lock_global_np();
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checkResults("pthread_lock_global_np() (main)\n", rc);
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}
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printf("Creating %d threads\n", THREADS);
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for (loop=0; loop<THREADS; ++loop) {
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rc = pthread_create(&threadid[loop], NULL, threadfunc, NULL);
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checkResults("pthread_create()\n", rc);
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}
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sleep(5);
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if (uselock) {
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rc = pthread_unlock_global_np();
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checkResults("pthread_unlock_global_np() (main)\n", rc);
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}
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printf("Wait for results\n");
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for (loop=0; loop<THREADS; ++loop) {
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rc = pthread_join(threadid[loop], NULL);
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checkResults("pthread_join()\n", rc);
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}
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printf("\nUsing %d threads and LOOPCONSTANT = %d\n",
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THREADS, LOOPCONSTANT);
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printf("Values are: (should be %d)\n", THREADS * LOOPCONSTANT);
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printf(" ==>%d, %d, %d, %d\n", i, j, k, l);
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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/TPMTXGLB0
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Give any number of parameters to show data corruption
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Creating 10 threads
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Wait for results
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Using 10 threads and LOOPCONSTANT = 50000
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Values are: (should be 500000)
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==>500000, 500000, 500000, 500000
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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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