Signal handler for the entire signal

Question

How can I register a signal handler for the ALL signal, available on the current OS, using signal (3)?

My code is as follows:

void sig_handler(int signum) { printf("Received signal %d\n", signum); } int main() { signal(ALL_SIGNALS_??, sig_handler); while (1) { sleep(1); }; return 0; } 

Answer 1

Most systems have an NSIG or _NSIG (the first of them will not be available in compliance mode because it violates the namespace) defined in signal.h , so the for loop for (i=1; i<_NSIG; i++) will skip all signals. In addition, on POSIX systems that have signal masks, CHAR_BIT*sizeof(sigset_t) is the upper limit on the number of signals that you could use as a reserve if neither NSIG nor _NSIG .

Answer 2

Signal handlers must deal with re-entry problems and other problems. In practice, it is often more convenient to mask signals and then extract them from time to time. You can mask all signals (except SIGSTOP and SIGKILL , which you cannot process in any way):

 sigset_t all_signals; sigfillset(&all_signals); sigprocmask(SIG_BLOCK, &all_signals, NULL); 

The code is a little different if you use pthreads. Call this on each thread, or (preferably) on the main thread, before creating any others:

 sigset_t all_signals; sigfillset(&all_signals); pthread_sigmask(SIG_BLOCK, &all_signals, NULL); 

Once you do this, you should periodically call sigtimedwait(2) as follows:

 struct timespec no_time = {0, 0}; siginfo_t result; int rc = sigtimedwait(&all_signals, &result, &no_time); 

If a signal is expected, information about it will be placed in result , and rc will be the signal number; if not, rc will be -1, and errno will be EAGAIN . If you are already calling select(2) / poll(2) (for example, as part of some event-driven system), you can create signalfd(2) and attach it to your event loop. In this case, you still need to mask the signals as shown above.