/* philosophers.c	dining philosophers using semaphores */
#include <signal.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <signal.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <pthread.h>
#define Philosophers 5


int room[2]; /* pipe file descriptors for use as a semaphores */
int frk[Philosophers][2];

void P( int sem[] ){
  char buf[1];

  read( sem[0], &buf, 1 );
}

void V( int sem[] ){
  char buf[1] = { 'a' };

  write( sem[1], &buf, 1 );
}

void *phil( void * arg ) { /* function for each philosopher */
  int *me, j;

  me = (int *) arg;

  for( j=0; j<3; j++ ) {
    P( room );		/* enter the room */
    P( frk[*me] );		/* acquire the */
    P( frk[(*me+1) % Philosophers] );  /* forks */

    printf( "Philosopher %d Eating !!\n", *me );
    srand( (int)time( NULL ) ); /* eat for between */
    sleep((rand() % 15) + 2);   /* 2 and 16 seconds */
    printf( "Philosopher %d Thinking!!\n", *me );

    V( frk[*me] );		/* release the forks */
    V( frk[(*me+1) % Philosophers] );
    V( room );		/* leave the room */
    sleep(rand() % 20); /* think for between 0 and 19 seconds */
  }
  pthread_exit( NULL );
}

int main( void ) {
  int i;
  pthread_t tid[Philosophers];
  int id[Philosophers];

  pipe( room );
  for( i=0; i<Philosophers; i++ )
    pipe( frk[i] ); 
  for( i=0; i<Philosophers-1; i++)  /* initialize room to 4 */
    V( room );
  for( i=0; i<Philosophers; i++ ) /* initialize each fork to 1 */
    V( frk[i] );
        
  for( i=0; i<Philosophers; i++ ) /* set up philosopher ids */
    id[i] = i;
  for( i=0; i<Philosophers; i++ )
    pthread_create( &tid[i], NULL, phil, (void *) &id[i] );
  for( i=0; i<Philosophers; i++ )
    pthread_join( tid[i], NULL );
  return 0;
}