specifies the operation of pthread_sigmask():
All signals in the set of this instance this set will be blocked, and all other signals will be unblocked.
All signals in the set of this instance this set will be blocked, and the blocking status of all other signals will remain unchanged.
All signals in the set of this instance this set will be unblocked, and the blocking status of all other signals will remain unchanged.
previous masked signals set (call its sigmask() method to restore the previous state)
In: how must be SIG_SETMASK, SIG_BLOCK or SIG_UNBLOCK. Note that ensuring this guarantees that pthread_sigmask() will always succeed.
Calls pthread_sigmask() with the set of signals of this instance.