pause()

之前一直以为pause就是将进程暂停，至于是怎么个暂停法，一直没有去深究。今天man了一下，才发现原来是wait for signal。

#include <unistd.h>

int pause(void);

DESCRIPTION

　　The pause() library function causes the invoking process (or thread) to sleep until a signal is received that either terminates it or causes it
to call a signal-catching function.

RETURN VALUE
　　The pause() function only returns when a signal was caught and the signal-catching function returned. In this case pause() returns -1, and errno
is set to EINTR.

ERRORS
　　EINTR a signal was caught and the signal-catching function returned.

pause函数使调用进程挂起直到捕捉到一个信号，只有执行了一个信号处理程序并从其返回时，pause才返回。在这种情况下，pause返回-1，并将errno设置为EINTR。

void sig_usr(int signo)
{
    if (signo == SIGUSR1)
        printf("received SIGUSR1
");
    else if (signo == SIGUSR2)
        printf("received SIGUSR2
");
    else
        printf("received signal %d
", signo);
}

static void sig_quit(int signo)
{
    printf("111caught SIGQUIT
");
    if (signal(SIGQUIT, SIG_DFL)==SIG_ERR)
    {
        printf("can't reset SIGQUIT
");
    }
}

static void sig_alrm(int signo)
{
    printf("caught alarm...
");
}

int main(int argc, char** argv)
{
    signal(SIGUSR1, sig_usr);
    signal(SIGQUIT, sig_quit);
    signal(SIGALRM, sig_alrm);

    printf("before pause......
");
    //raise(SIGQUIT);
    alarm(5);
    //pause();
    printf("after pause:%d
",pause());
    printf("errno:%s
", strerror(errno));
    //signal(SIGQUIT, SIG_DFL);

    return 0;
}

运行结果为：