6_sigaction_mask.c

#include <signal.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sched.h>
#include <string.h>

static int finished = 0;
static int id = 0;

static int
is_usr1_blocked(void)
{
	sigset_t old;
	sigprocmask(0, NULL, &old);
	return sigismember(&old, SIGUSR1);
}

static void
on_new_signal(int signum)
{
	int my_id = ++id;
	printf("Begin processing %d, usr1 block = %d\n", my_id,
	       is_usr1_blocked());
	if (my_id == 1)
		raise(signum);
	printf("End processing %d\n", my_id);
	++finished;
}

int
main(int argc, char **argv)
{
	struct sigaction act;
	act.sa_handler = on_new_signal;
	sigemptyset(&act.sa_mask);
	act.sa_flags = 0;
	for (int i = 1; i < argc; ++i) {
		if (strcmp(argv[1], "nodefer") == 0)
			act.sa_flags |= SA_NODEFER;
	}
	sigaction(SIGUSR1, &act, NULL);
	printf("Before raises, usr1 block = %d\n", is_usr1_blocked());
	raise(SIGUSR1);
	while (finished != 2)
		sched_yield();
	printf("After raises, usr1 block = %d\n", is_usr1_blocked());
	return 0;
}