in reply to Timing of garbage collection
As long as you keep references around to your objects, you'll be able to access them through those references, wherever they may live. Could be deep down some data structure, or maybe even in a closure — as long as parts of your code still have access to those references, those parts of the code will have access to the objects.
Ergo, as soon as an object is ready for garbage collection (i.e., you no longer have references pointing to them), no part of your code will be able to access those objects (I'm cutting corners here, because there's still the thing of weak references, but that's irrelevant to the discussion).
So if Outside Force throws an object index at you that has been used before and it is meant to represent the same object as before, then I hope you still have a reference to that object. However, if the non-new object index is a new object, and you don't have a reference to the old object around any more, then there's no problem at all. Whether or not perl has already garbage collected the old object, you won't be able to access it any more anyway.
So in the end, it's all your responsibility.
- Keep references to those objects that you will need again later, and you'll be able to get to those objects;
- Remove references to the objects that you're done with. Then, even when the Outside Force reuses an old index, you'll still be forced to create a fresh new object because as far as your code is concerned, the old object isn't anywhere to be found any longer