Is there an event for when garbage collection occurs in .NET?

Question

I've got a weird slowdown in my ASP.NET website that I cannot seem to track down. I'm suspecting that GC might be kicking in and halting my threads. To know for sure it would be nice to log every time when GC does occur.

I could make a dummy object and do the logging in its finalizer, but that would then be a one-shot solution, while in my case there are several such inexplainable pauses.

Any ideas?

Added: The environment is VS2008/.NET 3.5 SP1. And no, the Garbage Collection Notifications won't do because they are a method of polling, and don't work for a concurrent GC.

Answer 1

Here's a simple trick. It might not be 100% accurate, but it will probably be good enough.

If you can live with being notified of finalization, then there is a simple method you can use.

Create an object, and don't keep a reference to it. When the object is finalized, you raise your event, and then construct another object. You don't keep a reference to this object either, but it will live until the next time a complete enough collection is performed.

Here's such an object:

public class GCNotifier
{
    public static event EventHandler GarbageCollected;

    ~GCNotifier()
    {
        if (Environment.HasShutdownStarted)
            return;
        if (AppDomain.CurrentDomain.IsFinalizingForUnload())
            return;
        new GCNotifier();
        if (GarbageCollected != null)
            GarbageCollected(null, EventArgs.Empty);
    }

    public void Start()
    {
        new GCNotifier();
    }
}

If you want, you can add support for stopping it by having a static boolean field which prevents it from restarting itself upon next finalization.

Hope this is of some help.

Answer 2

The simple answer is "No there are not GC 'events' only the GCNotification function". However you create a wrapper class that will listen to GCNotification and that wrapper can fire events, but there is no simple event solution like you are looking for.

The reason for this is an event may or may not be processed before the GC completes. So what they have you do instead is spawn a child thread, sleep on WaitForFullGCApproach or pole if you are not looking for a Full GC, and do your whatever you need to do before the GC happens.

Answer 3

Perhaps Garbage Collection Notifications will help.

you can be notified that a full garbage collection is approaching