I originally posted this up as a question but I think it’s better suited here to be honest…
Apart from the whole of yesterday, I’ve never looked into memory leaks before. I knew roughly of it but had read about c# and garbage collection etc so thought it would never be a problem. However, I’m working on a custom editor window and part of it involves dynamically drawing a texture, this texture changes size (i have a zoom feature) and this is where the “problem” started. At the moment, I haven’t restricted the amount you can zoom, and I’m creating a new array the size of the texture every time the texture needs to redraw (only when zooming, so not every frame). I am also creating a new texture each time. Now I know both of these are bad practices and I know how to change them to make them efficient. However, I have kept them both in for my own testing purposes to help me try and understand how memory works.
So i noticed a problem when looking at task manager and the memory usage. When I zoomed (in or out) the memory gradually increased and never decreased. However, the further you zoom in, the memory increases by more. It doesnt take much to get the memory usage to 2 gig and then out of memory exceptions start getting thrown. Eventually Unity will freeze. So at first I thought it was the creating of a new texture each time rather than the array that was causing the problem. But after looking in the profiler, it turns out that 99% of the problem is the arrays. The textures memory allocation is actually handled extremely well from what I can gather. (it would never go above ~150Mb of used space for textures).
So I spent all of yesterday researching about Unity’s (monos) garbage collection etc. I read the 3 blog posts on gamasutra which were really good, but seemed like they might be a bit outdated now since 4.5 has come out. They also didn’t explain all the little details that I’m personally really interested in. The blog posts mention that mono for unity uses the Boehm garbage collector and not the Generational one. But this was on Unity 4.3 so is this still the case on 4.5? Because I ran some foreach tests (which are apparently bad in Unity) and yet I didn’t see any memory problems. I did many tests using different types (color, vector3, int, string, myownclass) and used a ridiculous (10,000,000) sized array. Infact, I noticed that I was only getting memory problems from my editor scripts. For example, my editor script starts creating arrays around the 9,000,000 mark if you zoom far enough and this is when the memory usage starts to get around 1.6 gig. But if I create a 9,000,000 sized array in a monobehavior script every frame, when I click play and monitor the profiler and task manager, theres no increase in memory at all, it stays roughly around the same amount. I really can’t get my head around it all.
Theres more… In the profiler under memory, you have your “used” memory and your “reserved” memory. I’ve read the info in the manual about it and all I learnt was that reserved memory for mono only goes up, never down. On top of that, the numbers in the profiler never match up to the number in task manager. I’ve read this is because the profiler doesnt account for some stuff that task manager does. I understand that, but what I don’t understand is how the numbers can be so far off from each other. For example I’ve had readings similar to these:
Used total: 200mb
Reserved total: 1.6gb
Task manager: 600mb
Used Total: 150mb
Reserved total: 400mb
Task Manager: 2GB
I’d understand if the reserved total was either always more or always less than the task manager amount. But it’s not, it varies so dramatically. Entering and exiting play mode and recompiling sometimes cause the memory usage to change in either task manager or the profiler, but again this is not stable either.
If anyone would be kind enough to explain to me about memory allocation in Unity (I honestly understand if no one can/wants to!!) or point me in the direction of some good reads (but I swear I’ve read nearly every forum post and article on google) I would really appreciate it!!
