omask = sigblock(mask);
long omask, mask;
mask = sigmask(signum)
Sigblock causes the signals specified in mask to be added to the set of signals currently being blocked from delivery. Signals are blocked
if the corresponding bit in mask is a 1; the macro sigmask is provided to construct the mask for a given signum.
It is not possible to block SIGKILL, SIGSTOP, or SIGCONT; this restriction is silently imposed by the system.