Advanced Programming in the UNIX® Environment

ptg10805159

456 Thread Control Chapter 12

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);

}

}

}

int

main(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);

}

Figure 12.16 Synchronous signal handling

Instead of relying on a signal handler that interrupts the main thread of control, we

dedicate a separate thread of control to handle the signals. We change the value of

quitflagunder the protection of a mutex so that the main thread of control can’t miss

the wake-up call made when we callpthread_cond_signal.Weuse the same mutex