George Clingerman started a discussion on the App Hub where he asks developers what they would like George and other MVPs to discuss with the XNA dev team.
I took the chance to request that improvements be made to the garbage collector (GC for short) on Xbox. What's wrong with the current one, you may ask? Unlike GC on the PC platform, the Xbox GC is non-generational. A generational (also called ephemeral) GC distinguishes between newly allocated objects and older objects. Reclaiming memory early from "young" objects makes it possible to diminish the frequency of reclaiming memory from older objects, because many young objects are short-lived. This is important as reclaiming memory from older objects is an expensive operation.
To work around this limitation, Shawn Hargreaves has written articles on how to minimize or avoid altogether garbage collection during gameplay phases which must run at a constant 60 fps. To summarize, there are two ways: Make sure each collection is fast (the so-called low latency path) or avoid allocating memory to avoid triggering garbage collections.
The good thing with the first approach is that you don't need to worry much about allocations that happen "behind your back", i.e. allocations that are introduced by the compiler or the core library. The bad thing is that you must avoid complex object graphs. Note that this includes even objects allocated outside of the performance-critical parts of your code, such as menu code, art assets...
The second approach is by far the most popular. It works well with object-oriented designs which rely on mutability. This approach also has problems. Developers must avoid all kinds of allocation at all time during gameplay, which implies refraining from using many language constructs. This includes events, delegates and lexical closures in C#, tuples and closures in F#.
Having two options to avoid performance drops due to GC sounds nice until you realize you can't combine the two. You have to choose one or the other, but you can't mix the two. That's sad, because in practice an attractive design for games is to use OOP and mutability for menus and low-level array-based computations for gameplay.
And this is why we need better garbage-collection on the Xbox.
