XNA's use of Collections

Eg:
LinkedList<Type> myLL = new LinkedList<Type>();
// add a bunch of things of Type to the collection...
for(int nLoop = 0; nLoop < myLL.Count; x++)
{
LinkedListNode<Type> cur = myLL[nLoop];
Type curType = cur.Value;
// Manipulate curType here
}

That same code could be turned into a foreach() call ( eg: foreach(Type curType in myLL) ), but as you said this generates some overhead which needs to be managed by the GC. You could also use a while() loop to do the same thing using the ability of the LinkedListNode<> class to traverse the list.

While I am using a LinkedList here, the same general principle works on any of your mentioned collection sets. Anything with the array sub-script overloaded can be done with a for() or while() loop. Try using one of those methods instead.

Neverwhere at 2007-9-4 >

Michael Hansen wrote:

the fastest collections build in net is a hashtable remove the using system.collections.generic use onlye system.collections; and a hasttable useng int as key and your class as value and do not use any struct use a class instead and keep the amount of classes small the class that you have as value .......................do not use any interfaces in thies classes a hashtable is slow to insert a item into but verry fast to pul out from

I'm sorry for the bluntness but this is just rubbish. Instead of paying any attention to that read something a little more authoritative like this explanation of the collection classes in .Net 2.0. Learn a little about how the collection classes work and you will be much better placed to know when to use which collection.

Cheers,
Leaf.

Leaf. at 2007-9-4 >

i have done some testing on the xbox360 both with generic and non generic

and a array and stack is not a collection

if you use a hashtable on the xbox360 with 4000 bounding boxed it is verry slow to inset a item into , but if you pull out from that table it is the fastest the overhead on a hashtable is 20 bytes in my test and if i use generic no mater what table i use it is 44 bytes even with linkedliist

so if you whant to get tings going fast use unsafe pointer to your hashtable

this can we do on the xbox360

so the memory overhead is a 4 bytes for a pointer

it allso prevent the garbge collector to interfear

and the speed of hashtable you are on the way

and a little tip of games developerment for scenegraph managerment us a kd-tree

MichaelHansen at 2007-9-4 >

Not that I'm agreeing with the idea of using a pointer to a hashtable but you can use unsafe code on the Xbox 360. Pointers, fixed pointers to managed objects and fixed buffers work but there appears to be a problem with stackalloc - code with stackalloc in causes an exception - not sure if that is a bug or by design. Not that I need to use stackalloc I was just experimenting.

Cheers,
Leaf.

Leaf. at 2007-9-4 >

<=?UTF-8?B?QWFyb24gTGVpYnk=?=@discussions.microsoft.com> spake the secret code

<ca093697-3be7-4347-a9f6-b5df4a42aa67@discussions.microsoft.com> thusly:

>[...] I'm still pretty new to C#, so what I'm

>wondering is if there are there ways to avoid this constant pressure on

>the GC -beyond hand unrolling the loops (in turn binding code to data),

>or rolling my own model classes, etc..

Computers are fast and cheap.

Programmers are slow and expensive.

Why are you optimizing for the fast and cheap part?

Just use the standard collections and the simplest code possible until

you've profiled your application and determined that this is actually

worth worrying about.

This isn't a C=64; don't program it like one.

--

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MVPUser at 2007-9-4 >

NNTP User wrote:

Its my understanding that you CANNOT use unsafe code blocks with XNA Game Studio Express. This is not the same thing as saying you can't do it on the Xbox 360, its just saying you can't do it with XNA GSE.

Is that you Richard? I'm guessing from the signature it is. Accessing these forums from NNTP doesn't seem to work too well, the formatting is gone and they are not that easy to read.

Anyway, regarding unsafe code on the Xbox 360 with XNA GSE, just try it, it works. I'm not talking about hacking something onto it, just create an Xbox game project, set it to build with the unsafe option and write some unsafe code. See Shawn's post in this thread for futher confirmation. Note, unsafe code refers to the use of pointers and fixed buffers not P/Invoke or other interop methods.

I found out a little more about stackalloc, it looks like the compact framework doesn't support it but the compiler doesn't spot it - so you end up with a runtime exception instead.

Cheers,
Leaf.

Leaf. at 2007-9-4 >