Check if the ThreadPool has any active threads

Question

I'm writing a windows service that responds to IMAP push notifications. When a notification is received I queue a user work item using ThreadPool. (The method it invokes puts some things in a database and etc).

At some point I want to stop my service which will stop the ThreadPool from queuing additional threads and wait until there are no open threads that are doing work.

//Pseudo code
public void StopService()
{
    while (true)
    {
        if (ThreadPool.ActiveThreads == 0)
        {
            //disconnect imap
            //stop service
        }
    }
}

Even better would be a way to tell the ThreadPool that I want to be notified that it has no active threads so that I don't have to poll it in a while loop.

This question uses a thread safe counter which is one way to figure out if the ThreadPool has any open threads, but surely there must be a flag or some method/property off the ThreadPool class to determine this?

Wouldn't the code that you're running be an active thread in the ThreadPool? — krillgar, Apr 08 '14 at 17:56
Sure why not? I wrote Pseudo code for a reason, it's to help visualize what I wrote. — The Muffin Man, Apr 08 '14 at 17:59
Well I was just thinking that it would be a reason why you'd never get inside of your `if` statement and stop your service. — krillgar, Apr 08 '14 at 18:00

Cam Bruce · Accepted Answer · 2014-04-08T18:54:06.307

2

I would suggest you hook up all your individual work items to a ManualResetEvent then queue up all your work items in the ThreadPool and then call WaitHandle.WaitAll(myResetEvents); to wait until all of your work items are complete, then close your service down, etc.

Program Flow

Start Service
Start Listening
Queue Work Items
Stop Listening for new items
Wait for all items to finish -WaitHandle.WaitAll(allMyQueuedWorkitems)
Stop Service

edited Apr 08 '14 at 18:54

answered Apr 08 '14 at 17:59

Cam Bruce

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So within the stop service method I should do `while(WaitHandle.WaitAll(...)){ //stop service //return;}`? – The Muffin Man Apr 08 '14 at 18:21
No, You would stop listening for new requests at some point, then wait for all existing queued items to complete, then call your close service method. See answer for updated program flow – Cam Bruce Apr 08 '14 at 18:55
Oh I see, I call stop service method and at that point I stop listening then put `WaitHandle.WaitAll` and after that goes my code to actually stop the service. It appears that by calling`WaitAll` won't execute the code after it until it's done. – The Muffin Man Apr 08 '14 at 19:04
Yes, by calling `WaitAll()`, it will block your main thread until all items you have queued have finished. – Cam Bruce Apr 08 '14 at 19:50

Check if the ThreadPool has any active threads

1 Answers1