(libc.info)Checking for Pending Signals


Checking for Pending Signals
----------------------------

   You can find out which signals are pending at any time by calling
`sigpending'.  This function is declared in `signal.h'.

 - Function: int sigpending (sigset_t *SET)
     The `sigpending' function stores information about pending signals
     in SET.  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
     `sigismember'; see Note: Signal Sets.)

     The return value is `0' if successful, and `-1' on failure.

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

   Here is an example.

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

   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 `SIGINT' signal is
pending when another `SIGINT' signal arrives, your program will
probably only see one of them when you unblock this signal.

   *Portability Note:* The `sigpending' function is new in POSIX.1.
Older systems have no equivalent facility.


automatically generated by info2www version 1.2.2.9