Flex loitering objects with 0 paths

Question

My application is leaking a visual component called GraphViewer. Every time the user changes graphs a new viewer is created and the old one is removed from the stage and discarded. Yet memory seems to leak. When I use the Flex profiler to track loitering objects it shows that GraphViewer instances indeed leak, but when I examine the object references of the loitering viewers I see that all of them (except one) have 0 paths to GC root.

I take a memory snapshot after GC and then change the graph (create a new viewer) N times. Then I do GC, take another snapshot and look at loitering objects. I see N GraphViewer objects loitering, but N-1 of them actually have 0 paths and only one has anything actually referencing it.

Why is the Flex profiler showing objects as loitering when they cannot be reached from the GC root? Is the Flex profiler reliable?

Answer 1

First off, why do you need to create a new instance of your component when new data arrives? Seems a bit wasteful. It's better to reuse an instance than to create a new one.

Second, it's hard to answer your issue without code, but often times the reason why a view component is kept in memory is because someone either still have a reference to it or an event listener hasn't been cleaned properly.

And lastly, there has been a known bug in the GC for some time now (though I haven't tested it recently; been about a year since I could reproduce) where large memory 'islands' (think of a very large module) won't clean up properly because the round trip algorithm for the GC won't figure that it's disconnected from the rest. To alleviate that, you might want to implement an IDisposable interface where your 'parent' view calls a destroy function before removing from stage (which then propagates throughout the component and it's children to destroy as well).

Good luck.