Do I need to call GC.KeepAlive(this) in my Dispose method?

Question

In this question @Jon skeet referenced this old blog post by the authority Chris Brumme.

I was wondering, do I need to follow all calls to GC.SuppressFinalize(this) with a GC.KeepAlive(this) to avoid weird race conditions where a finalizer can be invoked during the time a disposer is running in heavily multithreaded applications?

If so, can you come up with a sample program that exposes this bug?

Answer 1

No. GC.KeepAlive doesn't actually do anything; its purpose is to 'fool' the runtime into preventing a specific object from being garbage collected between the start of the method and the call to GC.KeepAlive.

Any method call will keep an object alive in this way: you could pass it to Console.WriteLine, call ToString, or even... GC.SuppressFinalize.

(Or as MSDN puts it:

The KeepAlive method performs no operation and produces no side effects other than extending the lifetime of the object passed in as a parameter.)

Answer 2

Just curious, in what scenario would this give a problem? Say the Dispose() method is past the point where it references any members of the object. What could go wrong with the finalizer freeing the object?

Answer 3

I was asked this recently by a colleague, and posted the answer on my blog, along with example code:

http://nitoprograms.blogspot.com/2009/08/q-if-dispose-calls-suppressfinalize-is.html

You may also be interested in other Disposable blog posts of mine, one of which explores when SuppressFinalize or KeepAlive is required.