Tuesday, June 11, 2013

Finalize()/dtor ^ Dispose()

--some keywords
manual -- Dispose() is NOT automatically invoked like Finalize(). Upper-layer programmers should but often forget to call it (Murphy's law)
** defensive -- better include a call to Dispose() in the dtor. Note dtor calling Dispose, not the other way round.

deterministic -- Dispose(). You can control when it takes place. For serious resource management, use Dispose, since Finalize() may be pending for a long time on the finalizer thread.

Q: So what resource release should I put into Dispose()?
A: eg: window handlers (HWND), database connections... For these resources, Finalize() is another layer of defence. See P210 [[C# For Java Programmers]] for an HWND example.

--[[accellerated C# 2010]] has a concise coverage of the finalizer pitfall. Here are a few pointers.
Any class with a custom dtor must implement IDisposable, according to this book.

The finalizer thread calls Finalize() on each thread in the finalizer queue. Finalize() method is virtual but not overridable in c# (despite some confusing MSDN articles). Instead, you define a dtor like in c++, and Finalize() would invoke your dtor before all base dtors, just like c++.

See also http://stackoverflow.com/questions/1076965/in-c-sharp-what-is-the-difference-between-a-destructor-and-a-finalize-method-in

If you need to do anything in the dtor, it's often better done in Dispose(). There is more than 1 reason to avoid custom dtor, so much so that I don't see any good reason to ever do it.

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http://www.linkedin.com/in/tanbin