/* 
 * deadlock.c: demonstration of deadlock
 *
 * CS50, Spring 2022
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <pthread.h>

/********** global variables *******/
pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t mutex2 = PTHREAD_MUTEX_INITIALIZER;

/********** function prototype *******/
void* print_i(void *ptr);
void* print_j(void *ptr);

/********** main *******/
int main() {
  pthread_t t1, t2;
  int iret1 = pthread_create(&t1, NULL, print_i, NULL);
  int iret2 = pthread_create(&t2, NULL, print_j, NULL);
 if (iret1 || iret2) {
    fprintf(stderr,"pthread_create failed: iret1=%d, iret2=%d\n", iret1, iret2);
    exit(1);
  }
  else {
    sleep(4);
  }
  exit(0); //never reached.
}

// These two functions will run concurrently.
void* print_i(void *ptr) {
  pthread_mutex_lock(&mutex1);
  //sleep(1);         // comment and it works!
  pthread_mutex_lock(&mutex2);
  printf("I am in i\n");
  pthread_mutex_unlock(&mutex2);
  pthread_mutex_unlock(&mutex1);
  return NULL;
}

void* print_j(void *ptr) {
  pthread_mutex_lock(&mutex2);
  //sleep(1);         // comment and it works!
  pthread_mutex_lock(&mutex1);
  printf("I am in j\n");
  pthread_mutex_unlock(&mutex1);
  pthread_mutex_unlock(&mutex2);
  return NULL;
}