/* cc thisfile.c -lthread -lpthread */
/*
 * <p>This program demonstrate a potential deadlock scenario
 * where two processes request the resources in a
 * circular chain.</p>
 *
 * <p>Here a deadlock is not guaranteed to happen, but it has
 * the potential.</p>
 */
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>

#define NO_SHARE 0

void *work1(void *);   /* thread routine */
void *work2(void *);   /* thread routine */
int v = 0;             /* global variable */

pthread_mutex_t first_mutex;
pthread_mutex_t second_mutex;

int  main(int argc, char *argv[]) {

  int i;
  pthread_t tid[2];

  printf("creating threads...\n");
  pthread_mutex_init(&first_mutex, NULL);
  pthread_mutex_init(&second_mutex, NULL);

  pthread_create(&tid[0], NULL, work1, NULL);
  pthread_create(&tid[1], NULL, work2, NULL);

  printf("joining threads...\n");

  pthread_join(tid[0], NULL);
  pthread_join(tid[1], NULL);


  return (0);
}  /* main */

void * work1(void *arg)   {

  char c;
  printf("in PID : %lu\n", pthread_self());
  fflush(stdout);

  pthread_mutex_lock(&first_mutex);
  pthread_mutex_lock(&second_mutex);

  v ++;
  printf("PID : %lu my v is %d\n", pthread_self(), v);
  fflush(stdout);

  /*
  printf("PID %lu Press <enter> to continue ...", pthread_self());
  scanf("%c", &c);
  */

  pthread_mutex_unlock(&second_mutex);
  pthread_mutex_unlock(&first_mutex);

  //  pthread_exit(0);
}

void * work2(void *arg)   {

  char c;

  printf("in PID : %lu\n", pthread_self());
  fflush(stdout);

  pthread_mutex_lock(&second_mutex);
  pthread_mutex_lock(&first_mutex);

  v ++;
  printf("PID : %lu my v is %d\n", pthread_self(), v);
  fflush(stdout);

  /*
  printf("PID %lu Press <enter> to continue ...", pthread_self());
  scanf("%c", &c);
  */

  pthread_mutex_unlock(&first_mutex);
  pthread_mutex_unlock(&second_mutex);

  //  pthread_exit(0);
}