Arguments

 

how

   An integer value that indicates how to change the set of masked
   signals. Use one of the following values:

   SIG_BLOCK     The resulting set is the union of the current set
                 and the signal set pointed to by the set argument.
   SIG_UNBLOCK   The resulting set is the intersection of the
                 current set and the complement of the signal set
                 pointed to by the set argument.
   SIG_SETMASK   The resulting set is the signal set pointed to by
                 the set argument.
 

set

   The signal set. If the value of the set argument is:

   o  Not NULL - It points to a set of signals used to change the
      currently blocked set.

   o  NULL - The value of the how argument is not significant, and
      the process signal mask is unchanged, so you can use the call
      to inquire about currently blocked signals.
 

o_set

   A non-NULL pointer to the location where the signal mask in
   effect at the time of the call is stored.