Description

   The sigwait function suspends the calling thread until at least
   one of the signals in the set argument is in the caller's set
   of pending signals. When this happens, one of those signals
   is automatically selected and removed from the set of pending
   signals. The signal number identifying that signal is then
   returned in the location referenced by sig.

   The effect is unspecified if any signals in the set argument are
   not blocked when the sigwait function is called.

   The set argument is created using the set manipulation functions
   sigemptyset, sigfillset, sigaddset, and sigdelset.

   If, while the sigwait function is waiting, a signal occurs that
   is eligible for delivery (that is, not blocked by the signal
   mask), that signal is handled asynchronously and the wait is
   interrupted.

   See also sigtimedwait and sigwaitinfo.

   See the "Error and Signal Handling" chapter of the VSI C RTL
   Reference Manual for more information on signal handling.