/* ===========================================
*   Lab 1 i C & UNIX
*  ==========================================
*      Semaforer
*  ==========================================
*   Christian Ohlsson, di7chro@cse.kau.se
*   Karlstads universitet
*   991110
* ===========================================
*/

#include <signal.h>
#include <stdio.h>

#define WAITTIME 3
#define PERMS 0000

int P(char *name){
   while(creat(name,PERMS) == -1) ;
}
void V(char *name){
   unlink(name);
}
void handleSig(){
   V("A");
   V("B");
   V("C");
   exit(0);
}
void A(){
   while(1) {
       P("A"); 
       write(1, "A", 1);
       V("B");
       sleep(WAITTIME);
       P("A");
       write(1, "A", 1);
       V("C");
       sleep(WAITTIME);
   }
}
void B(){ 
   while(1) {
       P("B");
       write(1, "B\n", 2);
       V("A");
   }
} 
void C() {
   while(1) {
       P("C");
       write(1, "C\n", 2);
       V("A");
   }
}
int main() {
   int pidA, pidB, stat;
   if((signal(SIGINT,  handleSig)) ==  SIG_ERR) {
       perror("\nCould not initialize signals\n"); 
       exit(0);
   }
   signal(SIGTERM, SIG_IGN); 
   P("B");
   P("C");
   if((pidA=fork()) > 0) {
      if((pidB=fork()) > 0) {
         A();
         waitpid(pidA, &stat, 0);
         waitpid(pidB, &stat, 0);
      }
      if(pidB == 0)
         C();
   }
   if(pidA == 0)
      B();
   perror("\nCould not fork.\n"); 
   return 0;
}