Example

     The following example shows how to set the signal mask to block
     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);