Boost thread_group thread limiter

Question

Am trying to limit the number of threads at anytime to be equal to utmost the number of cores available. Is the following a reasonable method? Is there a better alternative? Thanks!

    boost::thread_group threads;
    iThreads = 0;

    for (int i = 0; i <  Utility::nIterations; i++)
    {

        threads.create_thread(
            boost::bind(&ScenarioInventory::BuildInventoryWorker, this,i));

        thread_limiter.lock();
        iThreads++;
        thread_limiter.unlock();

        while (iThreads > nCores)
            std::this_thread::sleep_for(std::chrono::milliseconds(1)); 

    }

threads.join_all();


void ScenarioInventory::BuildInventoryWorker(int i)
{
    //code code code....

    thread_limiter.lock();
    iThreads--;
    thread_limiter.unlock();
}

score 0 · Accepted Answer · edited May 23 '17 at 11:50

What you are likely looking for is thread_pool with a task queue.

Have a fixed number of threads blocking an queue. Whenever a task is pushed onto the queue a worker thread gets signalled (condition variable) and processes the task.

That way you

don't have the (inefficient) waiting lock
don't have any more threads than the "maximum"
don't have to block in the code that pushes a task
don't have redundant creation of threads each time around

See this answer for two different demos of such a thread pool w/ task queue: Calculating the sum of a large vector in parallel

Boost thread_group thread limiter

1 Answers1