#include <pthread.h>
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <semaphore.h>

#define NUMLOOPS 100000

int x = 0;
sem_t sem;

void *loop(void *);
pthread_t create_thread(int);

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

  pthread_t t1, t2;
  void *arg;
  int collisions = 0;
  int percentage = 0;
  int status = 0;

  // Initialize the semaphore
  status = sem_init(&sem, 0, 1);
  
  if(status < 0) {
    perror("seminit failed: ");
    exit(-1);
  }

  // Create thread 1
  t1 = create_thread(1);

  // Create thread 2
  t2 = create_thread(2);

  // Wait for both threads to finish
  pthread_join(t1, NULL);
  pthread_join(t2, NULL);

  // Calculate the results
  collisions = (NUMLOOPS*2 - x)/2;
  percentage = 100*((double)collisions/NUMLOOPS);

  // Print out the results
  if(collisions != 0) {
    printf("Race Condition!  x = %d, should be %d\n", x, NUMLOOPS*2);
    printf("There were %d collisions!  That's %d%% of all loops\n", collisions, percentage);
  }  else {
    printf("No Race Condition.  x = %d\n", x);
  }
}

/*
 * Create a thread
 */ 
pthread_t create_thread(int arg) {

  int status;
  pthread_t thread;

  // Create the thread
  status = pthread_create(&thread, NULL, loop, (void *)arg);

  // Make sure it worked
  if(status < 0) {
    printf("status = %d, errno = %d\n", status, errno);
    perror("pthread_create 1 failed: ");
    exit(-1);
  }

  // Return the thread pointer
  return thread;
}


/*
 * This is the code run by the two threads
 */
void *loop(void *foo) {
  int i;

  // This sleep allows the other thread to start
  // running before this one gets into the loop
  sleep(1);

  printf("Thread %d running\n", (int)foo);

  // Increment x many times
  for(i = 0; i < NUMLOOPS; i++) {
    //sem_wait(&sem);
    x = x+1;
    //sem_post(&sem);
  }

  printf("Thread %d done\n", (int)foo);

  return(NULL);
}