The following example shows how to generate and use a signal
      mask that blocks only the SIGINT signal from delivery:

               #include <signal.h>
               int return_value;
               sigset_t newset;
                 . . .
               sigemptyset(&newset);
               sigaddset(&newset, SIGINT);
               return_value = sigprocmask (SIG_SETMASK, &newset, NULL);