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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"> |
| — 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 <signal.h> |
| #include <stddef.h> |
| |
| sigset_t base_mask, waiting_mask; |
| |
| sigemptyset (&base_mask); |
| sigaddset (&base_mask, SIGINT); |
| sigaddset (&base_mask, SIGTSTP); |
| |
| /* <span class="roman">Block user interrupts while doing other processing.</span> */ |
| sigprocmask (SIG_SETMASK, &base_mask, NULL); |
| ... |
| |
| /* <span class="roman">After a while, check to see whether any signals are pending.</span> */ |
| sigpending (&waiting_mask); |
| if (sigismember (&waiting_mask, SIGINT)) { |
| /* <span class="roman">User has tried to kill the process.</span> */ |
| } |
| else if (sigismember (&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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