barrier.c

/* Here the first n-1 threads arrive they block until the nth thread arrives,at which point all the threads may proceed */

#include<stdio.h>
#include<pthread.h>
#include<semaphore.h>
sem_t mutex,barrier;
int count=0,n;
void* fun1(void *arg)
{
	sem_wait(&mutex);
		
		printf("a1\n");
		count++;
	sem_post(&mutex);
	if(count==n){
		sem_post(&barrier);
	}
	sem_wait(&barrier);
		printf("b1\n");
	sem_post(&barrier);
}

void* fun2(void *arg)
{
	sem_wait(&mutex);
	
		printf("a2\n");
		count++;
	sem_post(&mutex);
	if(count==n){
		sem_post(&barrier);
	}
	sem_wait(&barrier);
		printf("b2\n");
	sem_post(&barrier);
}

void* fun3(void *arg)
{
	sem_wait(&mutex);
		
		printf("a3\n");
		count++;
	sem_post(&mutex);
	if(count==n){
		sem_post(&barrier);
	}
	sem_wait(&barrier);
		printf("b3\n");
	sem_post(&barrier);
}

main()
{
	n=3;
	pthread_t t[n];
	sem_init(&mutex,0,1);
	sem_init(&barrier,0,0);
	pthread_create(&t[0],0,fun1,0);
	pthread_create(&t[1],0,fun2,0);
	pthread_create(&t[2],0,fun3,0);
	pthread_join(t[0],0);
	pthread_join(t[1],0);
	pthread_join(t[2],0);
}