函式原型：
#include <signal.h>
int sigsuspend(const sigset_t *mask);
作用：
用於在接收到某個信號之前，臨時用mask替換進程的信號掩碼，並暫停進程執行，直到收到信號為止。
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，等待著開放的信號的喚醒。系統在接收到信號後，馬上就把現在的信號集還原為原來的，然後調用處理函式。
返回值：
sigsuspend返回後將恢復調用之前的的信號掩碼。信號處理函式完成後，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.
