The sigsuspend() function replaces the caller's signal mask with the set of signals pointed to by the set argument and suspends the caller until delivery of a signal whose action is either to
execute a signal catching function or to terminate the process.
If the action is to terminate the process, sigsuspend() does not return. If the action is to execute a signal catching function, sigsuspend() returns after the signal catching function returns. On return, the signal mask is restored to the set that existed
before the call to sigsuspend().
It is not possible to block those signals that cannot be ignored (see signal(3HEAD)); this restriction is silently imposed by the system.