Condition Variables

#include<stdio.h>
#include<unistd.h>
#include<pthread.h>
  
pthread_mutex_t mx;
pthread_cond_t cv;
volatile int flag = 0;
  
void *threadfn1(void *p)
{
    puts("thread1 start");
    pthread_mutex_lock(&mx);
    puts("thread1 after lock");
    while(flag==0)
    {
        pthread_cond_wait(&cv,&mx);
    }
    flag = 0;
    puts("thread 1 after wait");
    pthread_mutex_unlock(&mx);
  
    return NULL;
}
  
void *threadfn3(void *p)
{
    puts("thread3 start");
    pthread_mutex_lock(&mx);
    puts("thread3 after lock");
    while(flag==0)
    {
        pthread_cond_wait(&cv,&mx);
    }
    flag = 0;
    puts("thread 3 after wait");
    pthread_mutex_unlock(&mx);
  
    return NULL;
}
  
void *threadfn2(void *p)
{
    puts("thread2 before lock");
    pthread_mutex_lock(&mx);
    puts("thread2 after lock");
    flag=1;
    pthread_cond_signal(&cv);
    //pthread_cond_broadcast(&cv);
    puts("thread2 after signal");
  
    pthread_mutex_unlock(&mx);
    return NULL;
}
  
int main()
{
    pthread_t t1,t2,t3;
    pthread_mutex_init(&mx,NULL);
    // uncomment for test
    //pthread_cond_signal(&cv);
    //flag = 1;
    pthread_create(&t1,NULL,threadfn1,NULL);
    pthread_create(&t3,NULL,threadfn3,NULL);
    sleep(1);
    pthread_create(&t2,NULL,threadfn2,NULL);
    sleep(10);
    puts("end test");
    return 0;
}