Question

boost::condition_variable cond;
boost::mutex mut;
bool ready = false;

void consumer() {
    boost::mutex::scoped_lock lock(mut);
    while (!ready) {
         cond.wait(lock);
    }
}

void producer() {
    boost::mutex::scoped_lock lock(mut);
    ready = true;
    cond.notify_all();
    boost::this_thread::sleep(boost::posix_time::seconds(4));
}

Refer to the above code, I actually sleep the producer thread for 4 seconds after I call notify_all(). However, the consumer threads are actually woken up after 4 seconds. So how can I get around this and wake up the consumer threads immediately after I call notify_all() despite the 4 seconds sleep. Thanks in advance.

Answer 1

It has to do with the boost::mutex::scoped_lock lock(mut); in producer.
As the scope ends AFTER the sleep, the mutex is only released after it.

Try with that, if you want to keep your scoped_lock.

void producer() {
  {
    boost::mutex::scoped_lock lock(mut);
    ready = true;
    cond.notify_all();
  }
  boost::this_thread::sleep(boost::posix_time::seconds(4));
}