Info Node: (libc.info)Checking for Pending Signals
(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.
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