#include <stdio.h>
#include <stdlib.h>


#define N               5
#define BusyEating      1
#define BusyThinking    1
#define Left(p)         (p)
#define Right(p)        (((p)+1) %N)

typedef int * semaphore;
semaphore chopstick [N];

void signal (semaphore s);
void wait (semaphore s);


void pick_up (int me)
{
        if (me ==0) {
                wait (chopstick [Right(me)]);
                printf ("Philosopher %d picks up right chopstick\n", me);
                sleep (1);
                wait (chopstick [Left(me)]);
                printf ("Philosopher %d picks up left chopstick\n", me);
        }
        else {
                wait(chopstick [Left(me)]);
                printf ("Philosopher %d, picks up left chopstick\n", me);
                sleep (1);
                wait (chopstick[Right(me)]);
                printf ("Philosopher %d picks up right chopstick\n", me);

        }
}

void put_down (int me) {
        signal (chopstick[Left(me)]);
        signal (chopstick[Right(me)]);

}

void philosopher (int me) {
        char *s;
        int i=1;

        for (;;i++) {
                pick_up (me);
                s = i == 1 ? "st" : i == 2 ? "nd" : i == 3 ? "rd" : "th";
                printf ("Philosopher %d eating for the %d%s time\n", me, i, s);
                sleep (BusyEating);
                put_down (me);
                printf ("Philosopher %s thinking\n", me);
                sleep (BusyThinking);
         }
  
}
void wait (semaphore s) {
        int junk;
        if (read(s[0], &junk, 1) <=0) {
                printf ("Error: wait failed\n");
                exit (1);
        }
}
semaphore make_semaphore (void) {
        int *sema;
        sema = calloc (2, sizeof (int));

        pipe(sema);
        return;
}
void signal (semaphore s) {

        if (write (s[1], "x", 1) <=0) {
                printf ("Error: write () failed\n");
                exit (1);
        }
}

main () {

        int i;

        for (i = 0; i < N; i++) {
                chopstick [N] = make_semaphore ();
                signal (chopstick[i]);
        }
        for (i= 0; i < N-1; ++i) {
                if (fork () == 0) break;
        }
        philosopher (i);
}