[Boost-users] Boost.Asio thread pool - add/remove threads at runtime

[Vance Grkov]

I am creating a simple task and timer thread pool using Boost.Asio.

 

I am searching for the recommended way to dynamically add and remove threads to the thread pool. I don’t want to have to queue up tasks most of the time, only when the thread count gets very high (100s) queuing is ok, also I want for the thread count to go down to example 5 threads when there is no more work presented to the thread pool.  This is because some of the tasks can take some time to complete and I don't want to hold off other tasks when computer resource are still available.

 

Basically this is the solution I have in mind now. Given the following configuration values:

 

    gInitialThreadPoolSize = 4;

    gMaximumThreadPoolSize = 1024;

    gNumberOfThreadsDoingWork = 0;

 

And 2 events:

 

    HANDLE moreWorkAvailable;

    HANDLE exit;

 

Create a thread pool using this worker function:

 

    void ThreadWorkerFunction(boost::asio::io_service *io, boost::thread &thread)

    {

        for (;;) {

            HANDLE objects[] = { moreWorkAvailable, exit };

            errorCode = WaitForMultipleObjects(objects)

            if (errorCode == WAIT_OBJECT_0) { // More work is available, lets start processing...

                gNumberOfThreadsDoingWork++;

                io->run();

                gNumberOfThreadsDoingWork--;

                // When all work has been processed, go back to the original thread pool size

                if (threads.size() < gInitialThreadPoolSize ) {

                    threads.remove(thread);

                    break;

                }

            } else if (errorCode == WAIT_OBJECT_1) {

                threads.remove(thread);

                break;

            }

        }

    }

 

This is now the thread pool is created:

 

      std::vector<boost::shared_ptr<boost::thread> > threads;

      for (std::size_t i = 0; i < gInitialThreadPoolSize; ++i)

      {    

            boost::shared_ptr<boost::thread> thread(new boost::thread(

                  boost::bind(&ThreadWorkerFunction, &io, thread)

                  ));

            threads.push_back(thread);

      }

 

Next every time a task is inserted into the queue we check if all worker threads are busy, and in case they are busy, create a new thread

 

    if (threadsDoingWork  == threads.size()) {

        boost::shared_ptr<boost::thread> thread(new boost::thread(

              boost::bind(&worker, &io)

              ));

        threads.push_back(thread);

    }

    SetEvent(moreWorkAvailable);

 

Also in the ThreadWorkerFunction(...) function, after io->run() returns, we can check if more than N threads are idle and keep exiting until we get at minimum.

 

I would appreciate if you can let me know if there is some better and more simpler way to achieve this than implementing this myself. I am new to Asio so I might have overlooked something.

---

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[Ivan Dundek]

Hi.
Did you try the threadpool library based on BOOST ?
http://threadpool.sourceforge.net/
I tried it and the number of threads could be easily changed by calling
the resize() method of threadpool controller at any time.
Best regards
Dundee.

On Wed, 2010-04-14 at 21:34 +0000, Vance Grkov wrote:
> I am creating a simple task and timer thread pool using Boost.Asio.
>
>
>
> I am searching for the recommended way to dynamically add and remove
> threads to the thread pool. I don’t want to have to queue up tasks
> most of the time, only when the thread count gets very high (100s)
> queuing is ok, also I want for the thread count to go down to example
> 5 threads when there is no more work presented to the thread pool.
> This is because some of the tasks can take some time to complete and I
> don't want to hold off other tasks when computer resource are still
> available.
>
>
>
>
> Basically this is the solution I have in mind now. Given the following
> configuration values:
>
>
>
> gInitialThreadPoolSize = 4;
>

> gMaximumThreadPoolSize= 1024;

> ______________________________________________________________________

> Hotmail: Trusted email with powerful SPAM protection. Sign up now.

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> Boost-users mailing list
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[Vance Grkov]

Thanks for that, after looking at the threadpool library based on boost, I couldn't see the ability to handle timers (and my projects requires the ability to handle large number of timers). I will have to implement this myself. Boost.asio provides this using the deadline_timer class.
Regards!

 
> From: i.du...@cpce.net
> To: boost...@lists.boost.org
> Date: Thu, 15 Apr 2010 09:37:02 +0200
> Subject: Re: [Boost-users] Boost.Asio thread pool - add/remove threads at runtime
>
> Hi.
> Did you try the threadpool library based on BOOST ?
> http://threadpool.sourceforge.net/
> I tried it and the number of threads could be easily changed by calling
> the resize() method of threadpool controller at any time.
> Best regards
> Dundee.
>