the code is as follows:

static void sig_int (int);

int
main (void)
{

sigset_t    newmask, oldmask;

pr_mask("program start: ");

if (signal(SIGINT, sig_int) == SIG_ERR)
    err_sys("signal(SIGINT) error");
sigemptyset(&newmask);
sigaddset(&newmask, SIGINT);

/*
 * Block SIGINT and save current signal mask.
 */
if (sigprocmask(SIG_BLOCK, &newmask, &oldmask) < 0)
    err_sys("SIG_BLOCK error");

/*
 * Critical region of code.
 */

pr_mask("in critical region: ");

/*
 * Reset signal mask which unblocks SIGINT.
 */
if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0)
    err_sys("SIG_SETMASK error");

pr_mask("after  SIG_SETMASK: ");


pause();

/*
 * And continue processing ...
 */
pr_mask("program exit: ");

exit(0);

}

static void sig_int (int signo)
{

pr_mask("\nin sig_int: ");

}

the book says:

SIGINTpausepause

but I compile and run according to the above code, and press the ctrl+c, signal between the following two sentences to catch

pr_mask("after  SIG_SETMASK: ");
pause();

I don"t know how the situation in the book will happen.