Thread Wait For Parent

Question

I am implementing a simple thread pool mechanism for my ubuntu server (for my multi-client anonymous chat program), and I need to make my worker threads sleep until a job (i

Answer 1

The usual way this is implemented is to have a queue queue of outstanding work, a mutex mutex protecting the queue, and a wait condition queue_not_empty. Then, each worker thread does the following (using pseudo-api):

while (true) {
    Work * work = 0;
    mutex.lock();
    while ( queue.empty() )
       if ( !queue_not_empty.wait( &mutex, timeout ) )
           return; // timeout - exit the worker thread
    work = queue.front();
    queue.pop_front();
    mutex.unlock();
    work->perform();
}

The wait( &mutex, timeout ) call blocks until either the wait condition is signaled, or the call times out. The mutex passed is atomically unlocked inside wait(), and locked again before returning from the call, to provide a consistent view of the queue to all participants. timeout would be chosen rather large (seconds), and would lead to the thread exiting (the thread pool would start new ones if more work came in).

Meanwhile, the thread pool's work insertion function does this:

Work * work = ...;
mutex.lock();
queue.push_back( work );
if ( worker.empty() )
    start_a_new_worker();
queue_not_empty.wake_one();
mutex.unlock();