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

int counter = 0;
pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;

void *increment_counter(void *arg)
{ 
	pthread_mutex_lock(&lock);
	++counter;
	printf("Thread %lu Counter value: %d\n", (unsigned long)pthread_self(), counter);
	pthread_mutex_unlock(&lock);
	return NULL;
}

int main()
{
	pthread_t thread1, thread2;

	if (pthread_create(&thread1, NULL, increment_counter, NULL) != 0) {
		fprintf(stderr,"Creating first thread failed!");
		return -1;
	}

	if (pthread_create(&thread2, NULL, increment_counter, NULL) != 0) {
		fprintf(stderr,"Creating second thread failed!");
		return -1;
	}

	pthread_join(thread1, NULL);
	pthread_join(thread2, NULL); 

	return 0;
}