/* Program to shuffle a small deck of cards.   */
/* Usage:  cc -pthread -o shuffler shuffler.c  */
/*         ./shuffler                          */
/* Written by Carey Williamson, Oct 24/2008    */

/* This version uses two threads of control:  */
/*  - shuffler thread moves items around      */
/*  - printer thread prints out array         */

#include <stdio.h>
#include <pthread.h>

#define ARRAY_SIZE 8
#define LOOP_LIMIT 20

/* global variable shared by all threads */
int deck_of_cards[ARRAY_SIZE];

void *shuffler();  /* the thread for shuffling */
void *printer();   /* the thread for printing  */

/* Mutual exclusion (mutex) locks for thread coordination */
pthread_mutex_t array_mutex;

int main(int argc, char *argv[])
  {
    pthread_t tid1, tid2;   /* thread identifiers */
    pthread_attr_t attr;   /* set of thread attributes */
    int i;

    /* Initialize */
    for( i = 0; i < ARRAY_SIZE; i++ )
      deck_of_cards[i] = i+1;

    pthread_mutex_init(&array_mutex, NULL);

    /* get the default attributes */
    pthread_attr_init(&attr);

    /* create the first worker thread */
    pthread_create(&tid1, &attr, printer, NULL);

    /* create the second worker thread */
    pthread_create(&tid2, &attr, shuffler, NULL);

    /* wait for the first worker thread to exit */
    pthread_join(tid1, NULL);

    /* wait for the second worker thread to exit */
    pthread_join(tid2, NULL);

    /* output the final result */
    printf("All done, folks!\n");

  }

/* One thread to handle printing the array */
void *printer()
  {
    int i, counter;

    for( counter = 0; counter < LOOP_LIMIT; counter++ )
      {
	pthread_mutex_lock(&array_mutex);
	printf("Current contents of array: ");

	for( i = 0; i < ARRAY_SIZE; i++ )
	  printf(" %d", deck_of_cards[i]);
	printf("\n");

	pthread_mutex_unlock(&array_mutex);

	/* wait for a bit before next iteration */
	sleep( random() % 5 );
      }

    pthread_exit(0);
  }

/* One thread to handle shuffling */
void *shuffler()
  {
    int index1, index2, temp;
    int counter;

    for( counter = 0; counter < LOOP_LIMIT; counter++ )
      {
	pthread_mutex_lock(&array_mutex);

	index1 = random() % ARRAY_SIZE;
	index2 = random() % ARRAY_SIZE;
	printf("Shuffler: switching %d at pos %d with %d at pos %d\n",
	       deck_of_cards[index1], index1,
	       deck_of_cards[index2], index2);
	temp = deck_of_cards[index1];
	deck_of_cards[index1] = deck_of_cards[index2];
	deck_of_cards[index2] = temp;

	pthread_mutex_unlock(&array_mutex);

	/* wait for a bit before next iteration */
	sleep( random() % 5 );
      }

    pthread_exit(0);
  }