310 lines
8.5 KiB
HTML
310 lines
8.5 KiB
HTML
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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>sigwait()--Synchronously Accept a Signal</title>
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<body>
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<script type="text/javascript" language="Javascript" src="../rzahg/synch.js">
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<h2>sigwait()--Synchronously Accept a Signal</h2>
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<div class="box" style="width: 60%;">
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<br>
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Syntax<br>
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<pre>
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#include <signal.h>
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int sigwait( const sigset_t *set, int *sig );
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</pre>
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<br>
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Service Program Name: QPOSSRV1<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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</div>
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<p>The <strong>sigwait()</strong> function selects a pending signal from <em>
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set</em>, clears it from the set of pending signals for the thread or process,
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and returns that signal number in the location that is referenced by <em>
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sig</em>. If prior to the call to <strong>sigwait()</strong> there are multiple
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pending instances of a single signal number, upon successful return the number
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of remaining signals for that signal number is decremented by one.</p>
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<p>If no signal in <em>set</em> is pending at the time of the call, the thread
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shall be suspended. The thread does not resume until one or more signals in
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<em>set</em> become pending.</p>
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<p>The signals defined by <em>set</em> are required to be blocked at the time
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of the call to <strong>sigwait()</strong>; otherwise, <strong>
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sigwait()</strong> is not successful, and an [EINVAL] error is returned. The
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signals SIGKILL or SIGStop cannot be selected. Any attempt to use <strong>
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sigwait()</strong> to select these signals is simply ignored, and no error is
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returned.</p>
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<p>The signal action for the signal in <em>set</em> that is returned in the
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location referenced by <em>sig</em> is not taken.</p>
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<p>If more than one thread is using a <em>sigwait</em> function to wait for the
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same signal, only one of these threads will return from the <em>sigwait</em>
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function with the signal number. If more than one thread is waiting for the
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same signal, the first thread to wait on the signal will return from the <em>
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sigwait</em> function.</p>
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<br>
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<!-- Please NOTE: DO NOT DELETE THIS SECTION if this API has no authorities and locks. -->
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<!-- Instead, use the commented out coding below to indicate NONE. -->
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<h3>Authorities and Locks</h3>
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<!-- Use this if there are no authorities and locks. -->
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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><em>*set</em></strong></dt>
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<dd>(Input) A pointer to a signal set to be waited upon.<br>
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<br>
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</dd>
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<dt><strong><em>*sig</em></strong></dt>
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<dd>(Output) A pointer to the storage location where <strong>sigwait()</strong>
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can store the signal number that completed the wait.</dd>
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</dl>
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<br>
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<h3>Return Value</h3>
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<table cellpadding="5">
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<!-- cols="5 95" -->
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<tr>
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<td align="left" valign="top"><em>0</em></td>
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<td align="left" valign="top"><strong>sigwait()</strong> was successful.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>-1</em></td>
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<td align="left" valign="top"><strong>sigwait()</strong> was not successful.
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The <em>errno</em> variable is set to indicate the reason.</td>
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</tr>
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</table>
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<br>
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<br>
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<h3>Error Conditions</h3>
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<p>If <strong>sigwait()</strong> is not successful, <em>errno</em> usually
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indicates the following error. Under some conditions, <em>errno</em> could
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indicate an error other than that listed 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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<p>A function was passed incorrect argument values, or an operation was
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attempted on an object and the operation specified is not supported for that
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type of object.</p>
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<p>An argument value is not valid, out of range, or NULL.</p>
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<p>One of the following has occurred:</p>
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<ul>
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<li>The signal set pointed to by <em>set</em> contains a signal that is not
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within the valid range or a signal that is not supported.</li>
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<li>A signal in the signal set pointed to by <em>set</em> contains a signal
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that is not blocked.</li>
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</ul><br>
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<br>
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</dd>
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<dt><em>[ENOTSIGINIT]</em></dt>
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<dd>
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<p>Process not enabled for signals.</p>
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<p>An attempt was made to call a signal function under one of the following
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conditions:</p>
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<ul>
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<li>The signal function is being called for a process that is not enabled for
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asynchronous signals.</li>
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<li>The signal function is being called when the system signal controls have
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not been initialized.</li>
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</ul>
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</dd>
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</dl>
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<br>
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<h3>Usage Notes</h3>
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<p>The <strong>sigwait()</strong> function enables a process for signals if the
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process is not already enabled for signals. For details, see <a href=
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"sigesig.htm">Qp0sEnableSignals()--Enable Process for Signals</a>. If the
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system has not been enabled for signals, <strong>sigwait()</strong> is not
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successful, and an [ENOTSIGINIT] error is returned.</p>
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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>signal.h</strong>> file (see <a href="unix13.htm">Header
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Files for UNIX-Type Functions</a>)<br>
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<br>
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</li>
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<li><a href="sigdsig.htm">Qp0sDisableSignals()</a>--Disable Process for
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Signals<br>
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<br>
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</li>
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<li><a href="sigesig.htm">Qp0sEnableSignals()</a>--Enable Process for
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Signals<br>
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<br>
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</li>
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<li><a href="sigactn.htm">sigaction()</a>--Examine and Change Signal Action<br>
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<br>
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</li>
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<li><a href="sigpend.htm">sigpending()</a>--Examine Pending Signals<br>
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<br>
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</li>
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<li><a href="sigpmsk.htm">sigprocmask()</a>--Examine and Change Blocked
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Signals<br>
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<br>
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</li>
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<li><a href="sigsusp.htm">sigsuspend()</a>--Wait for Signal<br>
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<br>
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</li>
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<li><a href="sigtwait.htm">sigtimedwait()</a>--Synchronously Accept a Signal
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for Interval of Time<br>
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<br>
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</li>
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<li><a href="sigwaiti.htm">sigwaitinfo()</a>--Synchronously Accept a Signal and
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Signal Data</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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<p>The following example suspends processing by using the <strong>
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sigwait()</strong> function and determines the current time:</p>
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<p><strong>Note:</strong> The signal catching function is not called.</p>
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<pre>
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#include <signal.h>
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#include <unistd.h>
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#include <stdio.h>
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#include <time.h>
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extern int errno;
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void catcher( int sig ) {
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printf( "Signal catcher called for signal %d\n", sig );
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}
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void timestamp( char *str ) {
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time_t t;
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time( <em>T</em> );
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printf( "The time %s is %s\n", str, ctime(<em>T</em>) );
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}
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int main( int argc, char *argv[] ) {
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struct sigaction sigact;
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sigset_t waitset;
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int sig;
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int result = 0;
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sigemptyset( &sigact.sa_mask );
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sigact.sa_flags = 0;
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sigact.sa_handler = catcher;
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sigaction( SIGALRM, &sigact, NULL );
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sigemptyset( &waitset );
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sigaddset( &waitset, SIGALRM );
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sigprocmask( SIG_BLOCK, &waitset, NULL );
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alarm( 10 );
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timestamp( "before sigwait()" );
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result = sigwait( &waitset, &sig );
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if( result == 0 )
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printf( "sigwait() returned for signal %d\n", sig );
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else {
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printf( "sigwait() returned error number %d\n", errno );
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perror( "sigwait() function failed\n" );
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}
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timestamp( "after sigwait()" );
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return( result );
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}
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</pre>
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<h3>Output:</h3>
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<pre>
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The time before sigwait() is Tue Jul 15 11:15:43 1997
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sigwait() returned for signal 14
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The time after sigwait() is Tue Jul 15 11:15:54 1997
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</pre>
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<br>
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<hr>
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API introduced: V4R2
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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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"unix.htm">UNIX-Type APIs</a> | <a href="aplist.htm">APIs by 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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