void lock_stream() { 
     pthread_mutex_lock(&thread_lock); 
     if (0 < lock_handle) { 
         flock(lock_handle, LOCK_EX); 
     } 
 } 
  
 void unlock_stream() { 
     if (0 < lock_handle) { 
         flock(lock_handle, LOCK_UN); 
     } 
     pthread_mutex_unlock(&thread_lock); 
 }