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);