Arrays, Flash Vectors and a sawtooth memory pattern

[Rezmason]

Hey friends,

Last night I hunted down a really weird phenomenon in my NME project's Flash target. I was seeing a sawtooth graph for its memory usage in Adobe Scout, and after some digging I isolated the problem to a Haxe function that doesn't explicitly create objects.

What it does do is manipulate Arrays– although I didn't explicitly type the array variable. And by sampling object allocations with flash.sampler.Api, I discovered that Arrays indeed were the primary type of object being allocated as the project ran.

By replacing those Arrays with Flash Vectors (nme.Vector) and explicitly typing the variables in that function– now necessary, because otherwise Haxe's type inferencing seems to type the objects to Arrays– I managed to get rid of the sawtooth graph entirely. 

But would making this change have this effect? And how does a function that uses simple Array indexing end up creating Array objects when run? Was AS3's Array(obj) casting going on under the hood? That's my only hypothesis...

[Drakim]

That's interesting. Is it possible that the lack of a proper runtime type for the Array (as opposed to the vector) causes some sort of array cloning?

[Rezmason]

That's my latest theory– Arrays, as sparse data structures, might do weird things with memory on Flash compared to Vectors.

[David Peek]

Speaking of vectors, is there currently a way to create a vector directly (ie not via an array)? Does flash.Vector.ofArray([1,2,3]) compile into byte code for a vector literal?

The same goes for haxe.ds.Vector actually... it seems like it is backed by flash.Vector, java.NativeArray etc. but always requires you start with a haxe array. Is my understanding correct here?

David

[Cauê Waneck]

That's a good question, David. I've filed an issue about it

https://code.google.com/p/haxe/issues/detail?id=1801

Sorry for the minor topic derail! About the sawtooth memory pattern, I have no idea ;)

2013/5/9 David Peek <ninja...@gmail.com>

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[Nicolas Cannasse]

Le 10/05/2013 01:27, David Peek a �crit :

> Speaking of vectors, is there currently a way to create a vector
> directly (ie not via an array)? Does flash.Vector.ofArray([1,2,3])
> compile into byte code for a vector literal?

Sadly there's no bytecode for vector literal, so it would be necessary
to translate it to new Vector + several pushes. Not sure how much faster
it is than using the current way, especially for small vectors.

Best,
Nicolas

[Cauê Waneck]

Vector's push method can receive varargs. I don't know how this is implemented in the VM, or if it would be faster, but theoretically, we could just call a single push with all the array's arguments

2013/5/10 Nicolas Cannasse <ncan...@gmail.com>

[David Peek]

I wonder what the beautiful AS3 syntax "new <Int>[1,2,3]" compiles to then?

[Nicolas Cannasse]

Le 10/05/2013 14:34, David Peek a �crit :

> I wonder what the beautiful AS3 syntax "new <Int>[1,2,3]" compiles to then?

I think it will be same that flash.Vector.ofArray([1,2,3]), but I might
be wrong. Don't hesitate to check with a bytecode decompiler and report
it to me otherwise.

Best,
Nicolas

[Simon Krajewski]

http://simn.de/haxe/flash_signal.jpg

Let's see if Jan_Flanders notices the signal.

Simon

[Simon Richardson]

Each way is different depending on how you create a vector.

Note: this is built with http://wonderfl.net and Version 4.9.0 build 1425567 with playerglobal.swc for Flash Player 11.5. So could be different depending on which version of the compiler you're using.

1. var a : Vector.<int> = new <int>[1,2,3]; 
2. var a : Vector.<int> = Vector.<int>([1,2,3]);
3. var a : Vector.<int> = new Vector.<int>(); a[0] = 1; a[1] = 2; a[2] = 3;

Number 1.

12   findpropstrict Vector //nameIndex = 91

       14   getproperty   Vector //nameIndex = 92

       16   getlex         int //nameIndex = 5

       18   applytype     (1)

       20   pushbyte       3

       22   construct     (1)

       24   dup          

       25   pushbyte       0

       27   pushbyte       1

       29   setproperty   null //nameIndex = 93

       31   dup          

       32   pushbyte       1

       34   pushbyte       2

       36   setproperty   null //nameIndex = 93

       38   dup          

       39   pushbyte       2

       41   pushbyte       3

       43   setproperty   null //nameIndex = 93

       45   coerce         __AS3__.vec::Vector.<int> //nameIndex = 95

       47   setlocal1    

Number 2.

       12   getlex         Vector //nameIndex = 91

       14   getlex         int //nameIndex = 5

       16   applytype     (1)

       18   getglobalscope

       19   pushbyte       1

       21   pushbyte       2

       23   pushbyte       3

       25   newarray       [3]

       27   call           (1)

       29   coerce         __AS3__.vec::Vector.<int> //nameIndex = 93

       31   setlocal1   

Number 3.

       12   getlex         Vector //nameIndex = 91

       14   getlex         int //nameIndex = 5

       16   applytype     (1)

       18   construct     (0)

       20   coerce         __AS3__.vec::Vector.<int> //nameIndex = 93

       22   setlocal1    

       23   getlocal1    

       24   pushbyte       0

       26   pushbyte       1

       28   setproperty   null //nameIndex = 94

       30   getlocal1    

       31   pushbyte       1

       33   pushbyte       2

       35   setproperty   null //nameIndex = 94

       37   getlocal1    

       38   pushbyte       2

       40   pushbyte       3

       42   setproperty   null //nameIndex = 94

On 10 May 2013, at 14:57, Simon Krajewski <si...@haxe.org> wrote:

Am 10.05.2013 14:45, schrieb Nicolas Cannasse:

Le 10/05/2013 14:34, David Peek a écrit :

I wonder what the beautiful AS3 syntax "new <Int>[1,2,3]" compiles to then?

I think it will be same that  flash.Vector.ofArray([1,2,3]), but I might be wrong. Don't hesitate to check with a bytecode decompiler and report it to me otherwise.

http://simn.de/haxe/flash_signal.jpg

Let's see if Jan_Flanders notices the signal.

Simon