// 这个程序是 apue10.16 节图10_22中的代码.
#include "apue.h"
static void sig_int(int);
void pr_mask(const char*);
int
main(void)
{
sigset_t newmask, oldmask, waitmask;
pr_mask("program start: ");
if (signal(SIGINT, sig_int) == SIG_ERR)
err_sys("signal(SIGINT) error");
sigemptyset(&waitmask);
sigaddset(&waitmask, SIGUSR1);
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: ");
/*
* Pause, allowing all signals except SIGUSR1.
*/
if (sigsuspend(&waitmask) != -1)
err_sys("sigsuspend error");
pr_mask("after return from sigsuspend: ");
/*
* Reset signal mask which unblocks SIGINT.
*/
if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0)
err_sys("SIG_SETMASK error");
/*
* And continue processing ...
*/
pr_mask("program exit: ");
exit(0);
}
static void
sig_int(int signo)
{
pr_mask("\nin sig_int: ");
}
void
pr_mask(const char *str)
{
sigset_t sigset;
int errno_save;
errno_save = errno; /* we can be called by signal handlers */
if (sigprocmask(0, NULL, &sigset) < 0) {
err_ret("sigprocmask error");
} else {
printf("%s", str);
if (sigismember(&sigset, SIGINT))
printf(" SIGINT");
if (sigismember(&sigset, SIGQUIT))
printf(" SIGQUIT");
if (sigismember(&sigset, SIGUSR1))
printf(" SIGUSR1");
if (sigismember(&sigset, SIGALRM))
printf(" SIGALRM");
/* remaining signals can go here */
printf("\n");
}
errno = errno_save; /* restore errno */
}
执行
if (sigsuspend(&waitmask) != -1)
语句之后进程会被挂起并且会屏蔽除 SIGUSR1 之外的所有信号,.
1. 此时为什么 按 Ctrl+C 键入中断字符之后进程会被唤醒, 而通过 kill -USR1 PID 发送的SIGUSR1并不会使进程唤醒?
2. 将
if (sigsuspend(&waitmask) != -1)
改为
if (sigsuspend(&newmask) != -1)
之后, 进程应该会被挂起并且屏蔽除 SIGINT 之外的所有信号, 此时按Ctrl+C 键入中断字符为什么进程没有被唤醒?
