suspend1.c

#include "apue.h"

static void	sig_int(int);

int
main(void)
{
	sigset_t	newmask, oldmask, waitmask;

	pr_mask("program start: ");

	if (signal(SIGINT, sig_int) == SIG_ERR)
		err_sys("signal(SIGINT) error");
	sigemptyset(&waitmask);
	sigaddset(&waitmask, SIGUSR1);
	sigemptyset(&newmask);
	sigaddset(&newmask, SIGINT);

	/*
	 * Block SIGINT and save current signal mask.
	 */
	if (sigprocmask(SIG_BLOCK, &newmask, &oldmask) < 0)
		err_sys("SIG_BLOCK error");

	/*
	 * Critical region of code.
	 */
	pr_mask("in critical region: ");

	/*
	 * Pause, allowing all signals except SIGUSR1.
	 */
	if (sigsuspend(&waitmask) != -1)
		err_sys("sigsuspend error");

	pr_mask("after return from sigsuspend: ");

	/*
	 * Reset signal mask which unblocks SIGINT.
	 */
	if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0)
		err_sys("SIG_SETMASK error");

	/*
	 * And continue processing ...
	 */
	pr_mask("program exit: ");

	exit(0);
}

static void
sig_int(int signo)
{
	pr_mask("\nin sig_int: ");
}