The Linux Programming Interface

Signals: Advanced Features 467

e if (sigaction(SIGINT, &sa, NULL) == -1)
errExit("sigaction");
if (sigaction(SIGQUIT, &sa, NULL) == -1)
errExit("sigaction");

r for (loopNum = 1; !gotSigquit; loopNum++) {
printf("=== LOOP %d\n", loopNum);

/* Simulate a critical section by delaying a few seconds */

printSigMask(stdout, "Starting critical section, signal mask is:\n");

for (startTime = time(NULL); time(NULL) < startTime + 4; )

continue; /* Run for a few seconds elapsed time */

printPendingSigs(stdout,

"Before sigsuspend() - pending signals:\n");

if (sigsuspend(&origMask) == -1 && errno != EINTR)

errExit("sigsuspend");

}

t if (sigprocmask(SIG_SETMASK, &origMask, NULL) == -1)
errExit("sigprocmask - SIG_SETMASK");

y printSigMask(stdout, "=== Exited loop\nRestored signal mask to:\n");

/* Do other processing... */

exit(EXIT_SUCCESS);

}

–––––––––––––––––––––––––––––––––––––––––––––––––––– signals/t_sigsuspend.c

The following shell session log shows an example of what we see when running the

program in Listing 22-5:

$ ./t_sigsuspend

Initial signal mask is:

<empty signal set>

=== LOOP 1

Starting critical section, signal mask is:

2 (Interrupt)

3 (Quit)

Type Control-C; SIGINT is generated, but remains pending because it is blocked

Before sigsuspend() - pending signals:

2 (Interrupt)

Caught signal 2 (Interrupt) sigsuspend() is called, signals are unblocked

The last line of output appeared when the program called sigsuspend(), which

caused SIGINT to be unblocked. At that point, the signal handler was called and dis-

played that line of output.