Simple Mutex

#include<stdio.h>
#include<unistd.h>
#include<pthread.h>
  
pthread_mutex_t mx;
  
void *threadfn1(void *p)
{
    puts("thread1 start");
    pthread_mutex_lock(&mx);
    puts("thread1 after lock");
    sleep(2);
    pthread_mutex_unlock(&mx);
    puts("thread1 after unlock");
  
    return NULL;
}
  
void *threadfn2(void *p)
{
    puts("thread2 before lock");
    pthread_mutex_lock(&mx);
    puts("thread2 after lock");
    sleep(5);
    pthread_mutex_unlock(&mx);
    return NULL;
}
  
int main()
{
    pthread_t t1,t2;
    pthread_mutex_init(&mx,NULL);
    pthread_create(&t1,NULL,threadfn2,NULL);
    pthread_create(&t1,NULL,threadfn2,NULL);
    sleep(15);
    puts("end test");
    return 0;
}