sigsuspend

#include <signal.h>

int sigsuspend(const sigset_t *mask);

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.

也就是説，進程執行到sigsuspend時，sigsuspend並不會立刻返回，進程處於TASK_INTERRUPTIBLE狀態並立刻放棄CPU，等待UNBLOCK（mask之外的）信號的喚醒。進程在接收到UNBLOCK（mask之外）信號後，調用處理函數，然後還原信號集，sigsuspend返回，進程恢復執行。

sigsuspend返回後將恢復調用之前的的信號掩碼。信號處理函數完成後，進程將繼續執行。該系統調用始終返回-1，並將errno設置為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.