Structs and Garbage Collection

[RaudiusParticipant]

As I understand Structs (which is not very well btw), they are in essence a collection of primitives and pointers.

So in (my) theory creating (a lot of) structs should not constitute a problem in terms of garbage collection.

My concern is that I have entities that will require hit-testing with the ground each “Update()”. And the way I have currently implemented the hittesting it uses Rectf structs. Something like this:

Monkey

Class Entity Field x:Float Field y:Float Field w:Float Field h:Float Method ToRectf:Rectf() Return New Rectf(x, y, x+w, y+h) End ' This gets called every Update Method HitCheck(area:Rectf) SquareHitTest( ToRectf(), area ) End End

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Class Entity   Field x:Float   Field y:Float   Field w:Float   Field h:Float     Method ToRectf:Rectf()     Return New Rectf(x, y, x+w, y+h)   End     ' This gets called every Update   Method HitCheck(area:Rectf)      SquareHitTest( ToRectf(), area )   End End

My concern is that “ToRectf” is creating a new “Rect” struct each update never to be used again, so it somehow needs to be removed (if Rects were objects then it would be an issue).

If the struct values get interpreted as part of the call stack then that’s fine. But if it gets Garbage Collected (ie. during runtime the application has to check if there are instances of it elsewhere in the program) then that may cause unnecessary load and I’d be better off just passing the actual primitive float values to the HitTest function.

I’m not sure if I explained the problem well. tl;dr I am mostly wondering how the Monkey-Compiler interprets Structs and whether Structs need to be garbage collected or not.

[nerobotParticipant]

Using search in main forums page I found the same topic with lot info.

http://monkey2.monkey-x.com/forums/topic/structs-and-the-gc/

[codifiesParticipant]

a wiki would be great for little nuggets like this…

[RaudiusParticipant]

Thanks! I suppose it always pays to check the docs and forums.

So creating a struct and passing it around instead of primitives is basically the same as both the primitives and structs are “pass by value”.

[abakoboParticipant]

So creating a struct and passing it around instead of primitives is basically the same as both the primitives and structs are “pass by value”.

Yep. And using Structs is generaly a bit faster than classes as it is put on the stack and not on the heap.

[codifiesParticipant]

err careful there, passing a reference to a class could be a lot faster than copying (passing by value) a struct, especially if you’re structs got more than a few members…

Of course you can always pass a pointer to a struct….

[RaudiusParticipant]

I think for my specific case I’d rather be creating structs than objects since they are a one time use thing and creating objects would drastically increase the load on the GC, right?

I am just using “Rect” structs as a more convenient way to pass primitives (i.e. coordinates and dimensions for hit testing) and just wanted to make sure I am not making my game terribly inefficient in the process.

[abakoboParticipant]

In my experience the order of fastness is:
1-primitive
2-struct field
3-struct property

so avoid properties if it is not necessary

I played along with optimisation in this example: https://github.com/abakobo/learn_monkey2/tree/master/julia
The most optimised version I could get is not using structs because primitives where faster..
In the struct_non_optim example you can try 3 different manners to use structs with 3 very different speeds (by uncommenting/commenting). Field being the fastest one.

And here a little bit of code to illustrate the speed difference between struc and class with a simple object case:

Monkey

[crayon-5cba9c9f7c15e739282834 inline="true" ] #Import "<std>" Using std.. Struct structor Field x:Int Field y:Int Method New(a:Int,b:Int) x=a y=b End Method Add:Int() Return x+y End End Class classor Field x:Int Field y:Int Method New(a:Int,b:Int) x=a y=b End Method Add:int() Return x+y End End Function adds:int(a:Int,s:structor) Return a+s.Add() End Function addc:Int(a:Int,c:classor) Return a+c.Add() End Global ii:=2000 Global jj:=2000 Function Main() Local t:Int Local ta:Int Local add:Int Local c:classor Local s:structor ta=Millisecs() For Local j:=0 until jj For Local i:=0 until ii s=New structor (i+1,j+1) add=s.Add() Repeat add=add+s.Add() Until add>2000000 Next Next t=Millisecs()-ta Print "time struct: "+t ta=Millisecs() For Local j:=0 Until jj For Local i:=0 Until ii c=New classor (i+1,j+1) add=c.Add() Repeat add=add+c.Add() Until add>2000000 Next Next t=Millisecs()-ta Print "time class: "+t ta=Millisecs() For Local j:=0 until jj For Local i:=0 until ii s=New structor (i+1,j+1) add=s.Add() Repeat add=adds(add,s) Until add>2000000 Next Next t=Millisecs()-ta Print "time struct tru func (by value): "+t ta=Millisecs() For Local j:=0 Until jj For Local i:=0 Until ii c=New classor (i+1,j+1) add=c.Add() Repeat add=addc(add,c) Until add>2000000 Next Next t=Millisecs()-ta Print "time class tru func (by ref): "+t End

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107

[crayon-5cba9c9f7c15e739282834 inline="true" ] #Import "<std>" Using std..   Struct structor Field x:Int Field y:Int Method New(a:Int,b:Int) x=a y=b End Method Add:Int()    Return x+y End End   Class classor Field x:Int Field y:Int Method New(a:Int,b:Int) x=a y=b End Method Add:int()    Return x+y End End   Function adds:int(a:Int,s:structor) Return a+s.Add() End   Function addc:Int(a:Int,c:classor) Return a+c.Add() End   Global ii:=2000 Global jj:=2000   Function Main() Local t:Int Local ta:Int   Local add:Int   Local c:classor Local s:structor   ta=Millisecs() For Local j:=0 until jj For Local i:=0 until ii s=New structor (i+1,j+1) add=s.Add() Repeat add=add+s.Add() Until add>2000000 Next Next t=Millisecs()-ta Print "time struct: "+t ta=Millisecs() For Local j:=0 Until jj For Local i:=0 Until ii c=New classor (i+1,j+1) add=c.Add() Repeat add=add+c.Add() Until add>2000000 Next Next t=Millisecs()-ta Print "time class: "+t ta=Millisecs() For Local j:=0 until jj For Local i:=0 until ii s=New structor (i+1,j+1) add=s.Add() Repeat add=adds(add,s) Until add>2000000 Next Next t=Millisecs()-ta Print "time struct tru func (by value): "+t ta=Millisecs() For Local j:=0 Until jj For Local i:=0 Until ii c=New classor (i+1,j+1) add=c.Add() Repeat add=addc(add,c) Until add>2000000 Next Next t=Millisecs()-ta Print "time class tru func (by ref): "+t   End

[/crayon]

[RaudiusParticipant]

Damn you’re right parameters are much faster than structs! A lot faster!

I even made my own test to check the speed difference for a similar implementation  to the one in my game, and primitives values are significantly faster. As I understand it this has to do with the time it takes to copy structs from one method stack to the next.

I also found that using Getters to get the primitives also significantly affects the time it takes. I assume this is also to do with copying the (“pass-by-value”) value from the one method stack to the next as opposed to just reading it directly from the class’ memory in the heap.

I may have to consider changing my game to just passing the primitives separately (instead of combining them inside a struct) since the performance impact is so much more than I anticipated.

Thanks for the heads up!

<!–more–>

Monkey

#Import "<std>" Using std.. ' Calculate distance between two coordinates Function CalculateDistance:Float(pos1:Vec2f, pos2:Vec2f) Return CalculateDistance( pos1.X, pos1.Y, pos2.X, pos2.Y ) End Function CalculateDistance:Float(x1:Float, y1:Float, x2:Float, y2:Float) Local i := x1-x2 Local j := y1-y2 Return Sqrt(i*i + j*j) End ' Entity inside the "world" has x and y fields Class Entity Field x:Float Field y:Float ' entity is given a random coordinate in the world Method New() Self.x = Rand() Self.y = Rand() End ' Get Distance from Self to another entitiy in the "world" Method DistStruct(e:Entity) CalculateDistance(Self, e) ' passing Vec2f structs with coordinates End Method DistStructGet(e:Entity) CalculateDistance(GetVec2f(), e.GetVec2f()) ' passing Vec2f structs with coordinates End Method DistPrimsGet(e:Entity) CalculateDistance(GetX(), GetY(), e.GetX(), e.GetY()) ' passing primitive coordinate values End Method DistPrims(e:Entity) CalculateDistance(x, y, e.x, e.y) ' passing primitive coordinate values End Method GetX:Float() Return x End Method GetY:Float() Return y End Method To:Vec2f() Return New Vec2f(x, y) End Method GetVec2f:Vec2f() Return New Vec2f(GetX(), GetY()) End End ' The test involves calculating distances from each entity (in an array of entitties) to every entity '>in the same array. Const n := 5000 ' size of entitiy array Function Main() Local ents:Entity[] = New Entity[n] For Local i:=0 Until n ents[i] = New Entity() End Local t := Millisecs() '' CREATE AND PASS STRUCT TO DISTANCE CALC. FUNCTION '' For Local i:=0 Until n For Local j:=0 Until n ents[i].DistStruct(ents[j]) End End Print "Time DistStruct = " + (Millisecs()-t) t = Millisecs() '' CREATE AND PASS STRUCT (created using getters) TO DISTANCE CALC. FUNCTION '' For Local i:=0 Until n For Local j:=0 Until n ents[i].DistStructGet(ents[j]) End End Print "Time DistStruct (w/ getter) = " + (Millisecs()-t) t = Millisecs() '' PASS PRIMITIVES TO DISTANCE CALC. FUNCTION '' For Local i:=0 Until n For Local j:=0 Until n ents[i].DistPrims(ents[j]) End End Print "Time DistPrims = " + (Millisecs()-t) t = Millisecs() '' PASS PRIMITIVES (from getter) TO DISTANCE CALC. FUNCTION '' For Local i:=0 Until n For Local j:=0 Until n ents[i].DistPrimsGet(ents[j]) End End Print "Time DistPrims (w/ getter) = " + (Millisecs()-t) End Function Rand:Float() Return Rnd(100) End

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114

#Import "<std>" Using std..   ' Calculate distance between two coordinates Function CalculateDistance:Float(pos1:Vec2f, pos2:Vec2f) Return CalculateDistance( pos1.X, pos1.Y, pos2.X, pos2.Y ) End   Function CalculateDistance:Float(x1:Float, y1:Float, x2:Float, y2:Float) Local i := x1-x2 Local j := y1-y2 Return Sqrt(i*i + j*j) End       ' Entity inside the "world" has x and y fields Class Entity Field x:Float Field y:Float ' entity is given a random coordinate in the world Method New() Self.x = Rand() Self.y = Rand() End ' Get Distance from Self to another entitiy in the "world" Method DistStruct(e:Entity) CalculateDistance(Self, e) ' passing Vec2f structs with coordinates End Method DistStructGet(e:Entity) CalculateDistance(GetVec2f(), e.GetVec2f()) ' passing Vec2f structs with coordinates End Method DistPrimsGet(e:Entity) CalculateDistance(GetX(), GetY(), e.GetX(), e.GetY()) ' passing primitive coordinate values End Method DistPrims(e:Entity) CalculateDistance(x, y, e.x, e.y) ' passing primitive coordinate values End Method GetX:Float() Return x End Method GetY:Float() Return y End Method To:Vec2f() Return New Vec2f(x, y) End Method GetVec2f:Vec2f() Return New Vec2f(GetX(), GetY()) End End     ' The test involves calculating distances from each entity (in an array of entitties) to every entity '>in the same array.   Const n := 5000 ' size of entitiy array Function Main() Local ents:Entity[] = New Entity[n] For Local i:=0 Until n ents[i] = New Entity() End     Local t := Millisecs() '' CREATE AND PASS STRUCT TO DISTANCE CALC. FUNCTION '' For Local i:=0 Until n For Local j:=0 Until n ents[i].DistStruct(ents[j]) End End Print "Time DistStruct = " + (Millisecs()-t) t = Millisecs() '' CREATE AND PASS STRUCT (created using getters) TO DISTANCE CALC. FUNCTION '' For Local i:=0 Until n For Local j:=0 Until n ents[i].DistStructGet(ents[j]) End End Print "Time DistStruct (w/ getter) = " + (Millisecs()-t) t = Millisecs() '' PASS PRIMITIVES TO DISTANCE CALC. FUNCTION '' For Local i:=0 Until n For Local j:=0 Until n ents[i].DistPrims(ents[j]) End End Print "Time DistPrims = " + (Millisecs()-t) t = Millisecs() '' PASS PRIMITIVES (from getter) TO DISTANCE CALC. FUNCTION '' For Local i:=0 Until n For Local j:=0 Until n ents[i].DistPrimsGet(ents[j]) End End Print "Time DistPrims (w/ getter) = " + (Millisecs()-t) End   Function Rand:Float() Return Rnd(100) End

[nerobotParticipant]

One note about optimization: if your game works at desired fps you may don’t care about optimization if that brings difficult code styling.

[codifiesParticipant]

…and benchmarking, in the time it takes to test a few thousand calls, your PC could be doing something else, to stop doing it just in time for the next test, benchmarking is fraught potential pit falls…

[Author]

Posts