// Demo of Semaphores in C
 
#include <stdio.h> 
#include <pthread.h> 
#include <semaphore.h> 
#include <unistd.h> 

sem_t mutex; 

void* thread(void* arg) 
{ 
	//wait 
	sem_wait(&mutex); 
	printf("\n Thread Entering..\n"); 

	//critical section 
	printf("In critical section");
	sleep(4); 
	
	//signal 
	printf("\n Thread Exiting...\n"); 
	sem_post(&mutex); 
	return 0;
} 


int main() 
{ 
	sem_init(&mutex, 0, 1); 
	pthread_t t1,t2; 
	pthread_create(&t1,NULL,thread,NULL); // runs thread method on creation
	printf("\n Thread 1 ID: %i", t1);
	sleep(2); 
	pthread_create(&t2,NULL,thread,NULL); // runs thread method on creation
	printf("\n Thread 2 ID: %i", t2);
	pthread_join(t1,NULL); 
	pthread_join(t2,NULL); 
	sem_destroy(&mutex); 
	return 0; 
}