Bug 4550 - Finalizer is never executed
Summary: Finalizer is never executed
Alias: None
Product: Runtime
Classification: Mono
Component: GC ()
Version: unspecified
Hardware: PC Linux
: --- normal
Target Milestone: ---
Assignee: Rodrigo Kumpera
Depends on:
Reported: 2012-04-20 05:45 UTC by Marek Safar
Modified: 2012-04-20 19:25 UTC (History)
2 users (show)

Is this bug a regression?: ---
Last known good build:

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Description Marek Safar 2012-04-20 05:45:03 UTC
using System;
using System.Threading.Tasks;
using System.Threading;

class C
	public static void Main ()
		var mre = new ManualResetEvent (false);
		TaskScheduler.UnobservedTaskException += (o, args) => {
			Console.WriteLine ("From finalizer");
			args.SetObserved ();
			mre.Set ();
		while (true) {
			mre.Reset ();
			var inner = new ApplicationException ();
			CreateFaultedTaskCompletionSource (inner);
			GC.Collect ();
			Console.WriteLine ("WaitForPendingFinalizers");
			GC.WaitForPendingFinalizers ();
			Console.WriteLine ("Wait is over");
			if (!mre.WaitOne (5000))
				throw new ApplicationException ();

	static void CreateFaultedTaskCompletionSource (Exception inner)
		var tcs = new TaskCompletionSource<int> ();
		tcs.SetException (inner);
		tcs = null;

Just run it, it works reliably on .NET. I have tried both GCs, various settings but it does not work for me.
Comment 1 Marek Safar 2012-04-20 05:45:59 UTC
My output

From finalizer
Wait is over
Wait is over

Unhandled Exception: System.ApplicationException: An application exception has occurred.

I am not certain it's GC bug but for now it looks like one.
Comment 2 Rodrigo Kumpera 2012-04-20 12:05:35 UTC
Why a GC bug and not a PTL bug?
Comment 3 Rodrigo Kumpera 2012-04-20 12:06:28 UTC
The exception is been raised because TaskScheduler.UnobservedTaskException is not been fired, the GC doesn't fire events.
Comment 4 Rodrigo Kumpera 2012-04-20 19:25:26 UTC
This is caused by mono's conservative scanning, no bug here.