/* http://vip.cs.utsa.edu/usp/  dr.robbins utsa computer science  "unix systems programming" */
#include <errno.h>
#include <signal.h>
#include <stdio.h>

static volatile sig_atomic_t notifyflag = 1;
static int signal1 = 0;
static int signal2 = 0;

/* ARGSUSED */
static void turnon(int s) {
   notifyflag = 1;
}
 
/* ARGSUSED */
static void turnoff(int s) {
   notifyflag = 0;
}

/* ---------------------------Public functions --------------------------*/
int initnotify(int signo1, int signo2) {        /* set up for the notify */ 
   struct sigaction newact;

   signal1 = signo1;
   signal2 = signo2;
   newact.sa_handler = turnon;                 /* set up signal handlers */
   newact.sa_flags = 0;
   if ((sigemptyset(&newact.sa_mask) == -1) ||
       (sigaddset(&newact.sa_mask, signo1) == -1) ||
       (sigaddset(&newact.sa_mask, signo2) == -1) ||
       (sigaction(signo1, &newact, NULL) == -1))
       return -1;
    newact.sa_handler = turnoff;
    if (sigaction(signo2, &newact, NULL) == -1)
       return -1;
    return 0;
}
 
int waitnotifyon(void) {          /* Suspend until notifyflag is nonzero */
   sigset_t maskblocked, maskold, maskunblocked;
   
   if ((sigprocmask(SIG_SETMASK, NULL, &maskblocked) == -1) ||
       (sigprocmask(SIG_SETMASK, NULL, &maskunblocked) == -1) ||
       (sigaddset(&maskblocked, signal1) == -1) ||
       (sigaddset(&maskblocked, signal2) == -1) ||
       (sigdelset(&maskunblocked, signal1) == -1) ||
       (sigdelset(&maskunblocked, signal2) == -1) ||
       (sigprocmask(SIG_BLOCK, &maskblocked, &maskold) == -1))
      return -1;
   while (notifyflag == 0)
      sigsuspend(&maskunblocked);
   if (sigprocmask(SIG_SETMASK, &maskold, NULL) == -1)
      return -1;
   return 0;
}