#include "apue.h"#include <pthread.h>int			quitflag;	/* set nonzero by thread */sigset_t	mask;pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;pthread_cond_t waitloc = PTHREAD_COND_INITIALIZER;void *thr_fn(void *arg){	int err, signo;	for (;;) {		err = sigwait(&mask, &signo);		if (err != 0)			err_exit(err, "sigwait failed");		switch (signo) {		case SIGINT:			printf("\ninterrupt\n");			break;		case SIGQUIT:			pthread_mutex_lock(&lock);			quitflag = 1;			pthread_mutex_unlock(&lock);			pthread_cond_signal(&waitloc);			return(0);		default:			printf("unexpected signal %d\n", signo);			exit(1);		}	}}intmain(void){	int			err;	sigset_t	oldmask;	pthread_t	tid;	sigemptyset(&mask);	sigaddset(&mask, SIGINT);	sigaddset(&mask, SIGQUIT);	if ((err = pthread_sigmask(SIG_BLOCK, &mask, &oldmask)) != 0)		err_exit(err, "SIG_BLOCK error");	err = pthread_create(&tid, NULL, thr_fn, 0);	if (err != 0)		err_exit(err, "can't create thread");	pthread_mutex_lock(&lock);	while (quitflag == 0)		pthread_cond_wait(&waitloc, &lock);	pthread_mutex_unlock(&lock);	/* SIGQUIT has been caught and is now blocked; do whatever */	quitflag = 0;	/* reset signal mask which unblocks SIGQUIT */	if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0)		err_sys("SIG_SETMASK error");	exit(0);}