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。

 1 void sig_usr(int signo)
 2 {
 3     if (signo == SIGUSR1)
 4         printf("received SIGUSR1
");
 5     else if (signo == SIGUSR2)
 6         printf("received SIGUSR2
");
 7     else
 8         printf("received signal %d
", signo);
 9 }
10 
11 static void sig_quit(int signo)
12 {
13     printf("111caught SIGQUIT
");
14     if (signal(SIGQUIT, SIG_DFL)==SIG_ERR)
15     {
16         printf("can't reset SIGQUIT
");
17     }
18 }
19 
20 static void sig_alrm(int signo)
21 {
22     printf("caught alarm...
");
23 }

 1 int main(int argc, char** argv)
 2 {
 3     signal(SIGUSR1, sig_usr);
 4     signal(SIGQUIT, sig_quit);
 5     signal(SIGALRM, sig_alrm);
 6 
 7     printf("before pause......
");
 8     //raise(SIGQUIT);
 9     alarm(5);
10     //pause();
11     printf("after pause:%d
",pause());
12     printf("errno:%s
", strerror(errno));
13     //signal(SIGQUIT, SIG_DFL);
14 
15     return 0;
16 }

运行结果为：