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;
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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