| <html lang="en"> |
| <head> |
| <title>Checking for Pending Signals - The GNU C Library</title> |
| <meta http-equiv="Content-Type" content="text/html"> |
| <meta name="description" content="The GNU C Library"> |
| <meta name="generator" content="makeinfo 4.13"> |
| <link title="Top" rel="start" href="index.html#Top"> |
| <link rel="up" href="Blocking-Signals.html#Blocking-Signals" title="Blocking Signals"> |
| <link rel="prev" href="Blocking-for-Handler.html#Blocking-for-Handler" title="Blocking for Handler"> |
| <link rel="next" href="Remembering-a-Signal.html#Remembering-a-Signal" title="Remembering a Signal"> |
| <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> |
| <!-- |
| This file documents the GNU C library. |
| |
| This is Edition 0.12, last updated 2007-10-27, |
| of `The GNU C Library Reference Manual', for version |
| 2.8 (Sourcery G++ Lite 2011.03-41). |
| |
| Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002, |
| 2003, 2007, 2008, 2010 Free Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.3 or |
| any later version published by the Free Software Foundation; with the |
| Invariant Sections being ``Free Software Needs Free Documentation'' |
| and ``GNU Lesser General Public License'', the Front-Cover texts being |
| ``A GNU Manual'', and with the Back-Cover Texts as in (a) below. A |
| copy of the license is included in the section entitled "GNU Free |
| Documentation License". |
| |
| (a) The FSF's Back-Cover Text is: ``You have the freedom to |
| copy and modify this GNU manual. Buying copies from the FSF |
| supports it in developing GNU and promoting software freedom.''--> |
| <meta http-equiv="Content-Style-Type" content="text/css"> |
| <style type="text/css"><!-- |
| pre.display { font-family:inherit } |
| pre.format { font-family:inherit } |
| pre.smalldisplay { font-family:inherit; font-size:smaller } |
| pre.smallformat { font-family:inherit; font-size:smaller } |
| pre.smallexample { font-size:smaller } |
| pre.smalllisp { font-size:smaller } |
| span.sc { font-variant:small-caps } |
| span.roman { font-family:serif; font-weight:normal; } |
| span.sansserif { font-family:sans-serif; font-weight:normal; } |
| --></style> |
| <link rel="stylesheet" type="text/css" href="../cs.css"> |
| </head> |
| <body> |
| <div class="node"> |
| <a name="Checking-for-Pending-Signals"></a> |
| <p> |
| Next: <a rel="next" accesskey="n" href="Remembering-a-Signal.html#Remembering-a-Signal">Remembering a Signal</a>, |
| Previous: <a rel="previous" accesskey="p" href="Blocking-for-Handler.html#Blocking-for-Handler">Blocking for Handler</a>, |
| Up: <a rel="up" accesskey="u" href="Blocking-Signals.html#Blocking-Signals">Blocking Signals</a> |
| <hr> |
| </div> |
| |
| <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. |
| |
| </body></html> |
| |
