Question

The question I have might be more to do with semantics than with the actual use of IDisposable. I am working on implementing a singleton class that is in charge of managing a database instance that is created during the execution of the application. When the application closes this database should be deleted.

Right now I have this delete being handled by a Cleanup() method of the singleton that the application calls when it is closing. As I was writing the documentation for Cleanup() it struck me that I was describing what a Dispose() method should be used for i.e. cleaning up resources. I had originally not implemented IDisposable because it seemed out of place in my singleton, because I didn’t want anything to dispose the singleton itself. There isn’t currently, but in the future might be a reason that this Cleanup() might be called but the singleton should will need to still exist. I think I can include GC.SuppressFinalize(this); in the Dispose method to make this feasible.

My question therefore is multi-parted:

1) Is implementing IDisposable on a singleton fundamentally a bad idea?

2) Am I just mixing semantics here by having a Cleanup() instead of a Dispose() and since I’m disposing resources I really should use a dispose?

3) Will implementing ‘Dispose()’ with GC.SuppressFinalize(this); make it so my singleton is not actually destroyed in the case I want it to live after a call to clean-up the database.

Answer 1

In short, if you have a singleton and you call dispose. Any time that any object tries to use it after that, will be using an object in a disposed state.

Now putting it in, and disposing of the object after the application is done with it, isn’t necessarily bad. You do have to be careful though when you call it. If you are really concerned with the cleanup and you have only one reference to it, you can put the clean up code in the objects finalizer ~YourClass that way it will only be called with .Net is sure it is no longer needed (when the application closes, if it is a true singleton).

Am I just mixing semantics here by
having a Cleanup() instead of a
Dispose() and since I’m disposing
resources I really should use a
dispose?

Yes, this is just semantics. Dispose is the standard for showing there are things that need to be cleared up after the program is done with the object.

Will implementing ‘Dispose()’ with
GC.SuppressFinalize(this); make it so
my singleton is not actually destroyed
in the case I want it to live after a
call to clean-up the database.

No what this means is that when you call the dispose method, the Garbage Collector won’t call the object’s custom finalizer.