Trying to track down a Silverlight memory leak that only happens in browsers.

Question

This is an odd one. I am making a app that is kind of a game, and I wanted to have a shooting starburst effect. I made it one evening and it all worked well, until I noticed that my browser was eating over 300 megs of ram, eating 1 meg every 5 seconds, mainly when the starburst would happen.

Here is an example stripped down to just the starburst: http://www.sizzln.com/example.htm

First thought, I am not removing the objects or still have references somewhere. I am placing each generated star into a Canvas, but I am removing old starts every 3 seconds. I do have a lot of DoubleAnimations as well, but I even have a callback to set everything to null.

Here is the weird part, if I convert it to WPF it doesnt happen, if I run it inside of Silverlight Spy 3, it doenst happen. If I take a Heap Dump using WinDbg and SOS.dll, it reports that it should only be using between 1.8 and 3 MBs of ram.

I have the GC running every 3 seconds to cleanup, but it never has any effect. I can see in the heapdump that many objects are now deleted, and I always get back to 1.8 meg or so after a GC, but the memory shown in Task Manager just keeps going up.

I dont know what to do, I think I am carefully removing the objects unless my Heap is not being honest.

Answer 1

Are you running Vista or Win7? It sounds like the OS is not reclaiming memory, as it shouldn't unless it needs to.
It may also be that the Silverlight GC doesn't free its buffers, on the assumption that the memory may need to be reallocated soon.

In either case, it doesn't sound like anything to worry about, as long as the profiler says your program only uses 1.8MB after the GC runs.

Answer 2

I just briefly looked over your code. You have a lot of places where you hook into events (+=), but never unhook (-=). These are hard references and therefore won't ever be collected if they are ultimately connected to a root object.

Answer 3

OK I am going to sorta answer my own question. Silveright doesn't have the handy "BeginAnimation" method, so I found online a quick way to add an extension to do basically the same thing, it did this by creating a storyboard and starting it.

However, it just stayed there, I dont exactly know what it was being connected to either. Calling Stop() on it after it finishes fixed my memory issue.

One odd side effect is I have to be careful when I call the stop method, when creating so many storyboards it seemed to get a bit confused and it would cause some of the objects to reappear, even after they were removed from the control.