#include "apue.h"#include <setjmp.h>#include <time.h>static void						sig_usr1(int), sig_alrm(int);static sigjmp_buf				jmpbuf;static volatile sig_atomic_t	canjump;intmain(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 voidsig_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 voidsig_alrm(int signo){	pr_mask("in sig_alrm: ");}