Description

   The sigpending function stores the set of signals that are
   blocked from delivery and pending to the calling process in the
   location pointed to by the set argument.

   Call either the sigemptyset or the sigfillset function at least
   once for each object of type sigset_t prior to any other use of
   that object. If you do not initialize an object in this way and
   supply an argument to the sigpending function, the result is
   undefined.

   See also sigemptyset and sigfillset in this section.