linux c之sigsuspend 進程阻塞

函數原型：

#include <signal.h>

int sigsuspend(const sigset_t *mask);

作用：

用於在接收到某個訊號之前，臨時用mask替換進程的訊號掩碼，並暫停進程執行，直到收到訊號為止。

The sigsuspend() function replaces the current signal mask of the calling thread with the set of signals pointed to by sigmask and then suspends the thread until delivery of a signal whose action is either to execute a signal-catching function or to terminate the process. This will not cause any other signals that may have been pending on the process to become pending on the thread.

If the action is to terminate the process then sigsuspend() will never return. If the action is to execute a signal-catching function, thensigsuspend() will return after the signal- catching function returns, with the signal mask restored to the set that existed prior to thesigsuspend() call.

It is not possible to block signals that cannot be ignored. This is enforced by the system without causing an error to be indicated.

也就是說，sigsuspend後，進程 就掛在那裡，等待著開放的訊號的喚醒。系統在接收到訊號後，馬上就把現在的訊號集還原為原來的，然後調 用處理函數。

傳回值：

sigsuspend返回後將恢複調用之前的的訊號掩碼。訊號處理函數完成後，進 程將繼續執行。該系統調用始終返回-1，並將errno設定為EINTR.

Since sigsuspend() suspends process execution indefinitely, there is no successful completion return value. If a return occurs, -1 is returned and errno is set to indicate the error.

The sigsuspend() function will fail if:

[EINTR]

A signal is caught by the calling process and control is returned from the signal-catching function.

也就是說，sigsuspend後，進程就掛在那裡，等待著開放的訊號的喚醒。 系統在接受到訊號後，馬上就把現在的訊號集還原為原來的，然後調用處理函數。

Stevens在《Unix環 境進階編程》一書中是如是回答的“If a signal is caught and if the signal handler returns, then sigsuspend returns and the signal mask of the process is set to its value before the call to sigsuspend.”，由於sigsuspend是原子操作，所以這句給人的感覺就是先調用signal handler先返回，然後 sigsuspend再返回。

int main(void) {     sigset_t   newmask, oldmask, zeromask;           if (signal(SIGINT, sig_int) == SIG_ERR)        err_sys("signal(SIGINT) error");           sigemptyset(&zeromask);           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: ");           /* allow all signals and pause */   if (sigsuspend(&zeromask) != -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 ... */   exit(0);  }        static void sig_int(int signo) {     pr_mask("\nin sig_int: ");     return;  }

結果：

$a.outin critical region: SIGINT  ^C  in sig_int: SIGINT  after return from sigsuspend: SIGINT