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.