Question

I am trying to write a unit test using .NET 4 to ensure that an object can be garbage collected after some code is run. In Java, I would use assertGC to ensure that a weak reference is collected. How can I write this type of test for .NET?

I have tried keeping a WeakReference to the object and calling GC.Collect(), but as you’d expect, sometimes my object is collected and sometimes it is not. Note that this is for a unit test, not production code. I would not want GC.Collect() in my real code base.

I’m using C# but the same answer will be good for VB.NET too.

Answer 1

It looks like this isn’t possible at the moment with .NET 4. Though it is possible to know whether an object cannot be garbage collected (e.g. have a reference to it), there is no way to deterministically know whether an object can be garbage collected.

Using a WeakReference or a finaliser (and calling GC.Collect()) may collect the object, but unless it is in generation 0, there is a fair chance that it will not.

References:

• http://blogs.msdn.com/b/oldnewthing/archive/2010/08/11/10048629.aspx (found by https://stackoverflow.com/users/73070/joey)
• http://www.abhisheksur.com/2010/07/garbage-collection-algorithm-with-use.html