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

void *do_work(void *thr);
int counter = 0;
pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;

main(){
  pthread_t thread1;
  pthread_t thread2;
  char *thread1_identity = "Thread A: ";
  char *thread2_identity = "Thread B: ";
  int ret1 = pthread_create( &thread1, NULL, do_work, (void*)thread1_identity);
  int ret2 = pthread_create( &thread2, NULL, do_work, (void*)thread2_identity);
  pthread_join( thread1, NULL);
  pthread_join( thread2, NULL);

  exit(0); 	     
}
void *do_work(void *thr)
{
  char *thread_identity = (char*)thr;
  
  int HALT = 10;

  while( counter < HALT )
  {
    printf( "%s %d\n", thread_identity, counter );
    pthread_mutex_lock( &mtx);
    counter++;
    pthread_mutex_unlock( &mtx);
       sleep( 1 );
  }

}