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<h4 class="subsection">24.7.6 Checking for Pending Signals</h4>

<p><a name="index-pending-signals_002c-checking-for-2973"></a><a name="index-blocked-signals_002c-checking-for-2974"></a><a name="index-checking-for-pending-signals-2975"></a>
You can find out which signals are pending at any time by calling
<code>sigpending</code>.  This function is declared in <samp><span class="file">signal.h</span></samp>. 
<a name="index-signal_002eh-2976"></a>
<!-- signal.h -->
<!-- POSIX.1 -->

<div class="defun">
&mdash; Function: int <b>sigpending</b> (<var>sigset_t *set</var>)<var><a name="index-sigpending-2977"></a></var><br>
<blockquote><p>The <code>sigpending</code> function stores information about pending signals
in <var>set</var>.  If there is a pending signal that is blocked from
delivery, then that signal is a member of the returned set.  (You can
test whether a particular signal is a member of this set using
<code>sigismember</code>; see <a href="Signal-Sets.html#Signal-Sets">Signal Sets</a>.)

        <p>The return value is <code>0</code> if successful, and <code>-1</code> on failure. 
</p></blockquote></div>

   <p>Testing whether a signal is pending is not often useful.  Testing when
that signal is not blocked is almost certainly bad design.

   <p>Here is an example.

<pre class="smallexample">     #include &lt;signal.h&gt;
     #include &lt;stddef.h&gt;
     
     sigset_t base_mask, waiting_mask;
     
     sigemptyset (&amp;base_mask);
     sigaddset (&amp;base_mask, SIGINT);
     sigaddset (&amp;base_mask, SIGTSTP);
     
     /* <span class="roman">Block user interrupts while doing other processing.</span> */
     sigprocmask (SIG_SETMASK, &amp;base_mask, NULL);
     ...
     
     /* <span class="roman">After a while, check to see whether any signals are pending.</span> */
     sigpending (&amp;waiting_mask);
     if (sigismember (&amp;waiting_mask, SIGINT)) {
       /* <span class="roman">User has tried to kill the process.</span> */
     }
     else if (sigismember (&amp;waiting_mask, SIGTSTP)) {
       /* <span class="roman">User has tried to stop the process.</span> */
     }
</pre>
   <p>Remember that if there is a particular signal pending for your process,
additional signals of that same type that arrive in the meantime might
be discarded.  For example, if a <code>SIGINT</code> signal is pending when
another <code>SIGINT</code> signal arrives, your program will probably only
see one of them when you unblock this signal.

   <p><strong>Portability Note:</strong> The <code>sigpending</code> function is new in
POSIX.1.  Older systems have no equivalent facility.

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