Locking finalizer keeping app alive

[adamsitnik]

While working on dotnet/performance#1049 I've found that following app never quits:

using System;
using System.Collections.Concurrent;
using System.Threading;

namespace Neverending
{
    class Program
    {
        static void Main()
        {
            new Thread(() =>
            {
                while(true)
                {
                    GC.KeepAlive(new ConcurrentBag<string>());
                }
            }).Start();

            Console.WriteLine("Going to sleep");

            Thread.Sleep(TimeSpan.FromSeconds(3));

            Console.WriteLine("Woke up!");
        }
    }
}

@stephentoub is this expected behavior?

edit: simpler repo

[stephentoub]

This isn't specific to ConcurrentBag. The same pattern it employs with a finalizer that locks has the same behavior:

using System;
using System.Threading;

class Program
{
    static void Main()
    {
        new Thread(() => { while (true) GC.KeepAlive(new Finalizable()); }) { IsBackground = true }.Start();
        Console.WriteLine("Going to sleep");
        Thread.Sleep(TimeSpan.FromSeconds(3));
        Console.WriteLine("Woke up!");
    }
}

class Finalizable
{
    private static readonly object s_lock = new object();

    ~Finalizable()
    {
        lock (s_lock) { }
    }
}

[joperezr]

I assume this is not a regression so I have set milestone to future. Feel free to pull it back to 5.0 otherwise.