// Source: https://www.linuxprogrammingblog.com/code-examples/blocking-signals-with-sigprocmask

/** This program blocks SIGTERM signal for 2 seconds using sigprocmask(2)
 * After that the signal is unblocked and the queued signal is handled.  */
 
#include <signal.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

 
static int got_signal = 0;
 
static void hdl (int sig) {
	got_signal = 1; }
	
int main (int argc, char *argv[]) {
	sigset_t mask;
	sigset_t orig_mask;
	struct sigaction act;
 	memset (&act, 0, sizeof(act));
	act.sa_handler = hdl;
 	if (sigaction(SIGTERM, &act, 0)) {
		perror ("sigaction");
		return 1; }
	printf ("Emptying signal set...\n");
	sigemptyset (&mask);
	printf ("Adding SIGTERM to signal set...\n");
	sigaddset (&mask, SIGTERM);
	// SIGTERM signal is added to orig_mask
	printf ("Adding signal set to the original mask...\n");
 	if (sigprocmask(SIG_BLOCK, &mask, &orig_mask) < 0) {
		perror ("sigprocmask");
		return 1; }
 	// SIGTERM signal is blocked
 	printf ("Blocking SIGTERM signal...\n");
 	if (sigprocmask(SIG_SETMASK, &orig_mask, NULL) < 0) {
		perror ("sigprocmask");
		return 1; }
	printf ("Sleeping for 2 seconds\n");
 	sleep (2);		
  	if (got_signal) puts ("Got signal");
 	return 0; }