Error while unloading appdomain. (Exception from HRESULT: 0x80131015), inside Windows Service

Question

I receive this error in a windows service. This is the same service that I've previously discussed in my question here

The code is revised to use Parallel.ForEach (my own version as this is a 3.5 windows service). The reason for the Parallel use is down to the fact that it simply took too long to Unload each domain and running them in parallel should prove to be faster (appears to be even though there is only one thread that's doing each Unload?!).

Based on other posts, I can only guess that this is somehow down to the fact I am using a ThreadPool Thread to Unload the AppDomains. I just can't see how to avoid it?

public partial class SomeService : ServiceBase
{
    private Manager _appDomainManager;

    protected override void OnStop()
    {
        _appDomainManager.Dispose();
    }
}

public class Manager : IDisposable
{
    public void Dispose()
    {
        Log.Debug("Disposing");
        Dispose(true);
        GC.SuppressFinalize(this);
    }

    protected virtual void Dispose(bool disposing)
    {
        if (_disposed) return;
        if (disposing)
        {
            // dispose managed resources
            Parallel.For(0, appdomains.Length, UnloadAppDomian);
        }

        _disposed = true;
    }
}

private UnloadAppDomain(int appDomainIndex);

public static class Parallel35
{
    public static void For(int start, int end, Action<int> action)
    {
        var waitHandles = new WaitHandle[end - start];
        for (int j = 0; j < waitHandles.Length; j++)
        {
            waitHandles[j] = new ManualResetEvent(false);
        }

        for (int i = start; i < end; i++)
        {
            int i1 = i - start;
            ThreadPool.QueueUserWorkItem(
                state =>
                {
                    try
                    {
                        action((int) state);
                    }
                    finally
                    {
                        ((ManualResetEvent) waitHandles[i1]).Set();
                    }
                }, i);
        }
        WaitHandle.WaitAll(waitHandles);
    }
}

Sigridsigsmond

Have you tried attaching a debugger to your service to see exactly when this is happening using the Threads window? By the way, have you tried to unload all AppDomains in a single background task instead of one background task for each AppDomain? – Disarray

@PanosRontogiannis the problem was when I ran it in a single background thread it simply took too long for OnStop to exeute. Still investigating with some suspicions as to the problem. – Sigridsigsmond

Answer 1

I tracked down this as a bug to one of the AppDomains on exit waiting for a WaitHandle that's never set.

If a thread does not abort, for example because it is executing unmanaged code, or because it is executing a finally block, then after a period of time a CannotUnloadAppDomainException is thrown in the thread that originally called Unload.

The AppDomain now unloads relatively quickly and my service stops quite quickly.

Sigridsigsmond

Thanks to this five year old message, I resolved my own exception by replacing two destructor blocks with invokable cleanup routines, so that the AppDomain unloaded after I wash finished with it, but before the objects were destroyed. – Irritability

@David A. Gray can you please share your solution? – Kumar

Answer 2

Try to unload all AppDomains in a single background task instead of one background task for each AppDomain and use ServiceBase.RequestAdditionalTime so that the SCM does not mark your service as not responsive.

Disarray