mask.c

#include "apue.h"
#include <setjmp.h>
#include <time.h>

static void						sig_usr1(int);
static void						sig_alrm(int);
static sigjmp_buf				jmpbuf;
static volatile sig_atomic_t	canjump;

int
main(void)
{
	if (signal(SIGUSR1, sig_usr1) == SIG_ERR)
		err_sys("signal(SIGUSR1) error");
	if (signal(SIGALRM, sig_alrm) == SIG_ERR)
		err_sys("signal(SIGALRM) error");

	pr_mask("starting main: ");		/* {Prog prmask} */

	if (sigsetjmp(jmpbuf, 1)) {

		pr_mask("ending main: ");

		exit(0);
	}
	canjump = 1;	/* now sigsetjmp() is OK */

	for ( ; ; )
		pause();
}

static void
sig_usr1(int signo)
{
	time_t	starttime;

	if (canjump == 0)
		return;		/* unexpected signal, ignore */

	pr_mask("starting sig_usr1: ");

	alarm(3);				/* SIGALRM in 3 seconds */
	starttime = time(NULL);
	for ( ; ; )				/* busy wait for 5 seconds */
		if (time(NULL) > starttime + 5)
			break;

	pr_mask("finishing sig_usr1: ");

	canjump = 0;
	siglongjmp(jmpbuf, 1);	/* jump back to main, don't return */
}

static void
sig_alrm(int signo)
{
	pr_mask("in sig_alrm: ");
}