AS3 String Memory Leak

Question

I've been programming for some time in AS3 and found a really weird problem with strings that for no apparent reason are hanging on the memory, the program below just changes the label.text property with a random string, it works fine but when i looked at the Flex profiler i noticed that the number of Strings is increasing steadly, i tried executing the garbage collector but didnt helped me.

Is this a memory leak? how can i solve it?

As I know this strings should be collected by the garbage collector because there are no objects referencing them, yet this is not happening for all the strings.

Heres the code and a screenshot of the Flex profiler showing the number of String instances.

<?xml version="1.0" encoding="utf-8"?>
<s:WindowedApplication xmlns:fx="http://ns.adobe.com/mxml/2009" 
                   xmlns:s="library://ns.adobe.com/flex/spark" 
                   xmlns:mx="library://ns.adobe.com/flex/mx" creationComplete="windowedapplication1_creationCompleteHandler(event)">
<s:layout>
    <s:BasicLayout/>
</s:layout>
<fx:Script>
    <![CDATA[
        import mx.events.FlexEvent;

        protected var t:Timer=new Timer(10);

        protected function windowedapplication1_creationCompleteHandler(event:FlexEvent):void
        {
            t.addEventListener(TimerEvent.TIMER,listener,false,0,true);
            t.start();
        }

        protected function listener(e:Event):void
        {
            var s:String=Math.random()+"-->";
            this.fx(s);
            s=null;
        }

        protected function fx(s:String):void
        {
            this.label.text=s;
        }
    ]]>
</fx:Script>
<fx:Declarations>
    <!-- Place non-visual elements (e.g., services, value objects) here -->
</fx:Declarations>
<s:Label id="label" y="39" left="10" right="10" text="Label"/>
</s:WindowedApplication>

Sorry, less than 10 points, heres the profilers screenshot http://imageshack.us/a/img11/9716/stackw.png

SOLVED

Baris and Loxxy you were right, i made some changes in order to isolate the problem and it grows up to ~30Mb then the garbage collector frees some memory, it never goes back to ~2mb (starting point) but the graph starts to go from ~20mb to ~30mb over and over.

Heres the code to test this

<?xml version="1.0" encoding="utf-8"?>
<s:WindowedApplication xmlns:fx="http://ns.adobe.com/mxml/2009" 
                   xmlns:s="library://ns.adobe.com/flex/spark" 
                   xmlns:mx="library://ns.adobe.com/flex/mx" creationComplete="windowedapplication1_creationCompleteHandler(event)">
<s:layout>
    <s:BasicLayout/>
</s:layout>
<fx:Script>
    <![CDATA[
        import mx.events.FlexEvent;
        protected var maxMemoryUsage:Number=0;
        protected var i:Number=0;

        protected function windowedapplication1_creationCompleteHandler(event:FlexEvent):void
        {
            setTimeout(Fx,20);
        }

        protected function Fx():void
        {
            if(i++%1024==0) 
            {
                var mem:Number=System.totalMemory;
                this.maxMemoryUsage = mem>this.maxMemoryUsage?mem:this.maxMemoryUsage;
                trace(this.maxMemoryUsage + ' / ' + mem);
            }

            var s:String="";
            s+=Math.random().toString()+"qwertyuiu...1024 random chars...iiwqe";
            this.aSimpleString=s;
            setTimeout(Fx,20);
        }
    ]]>
</fx:Script>
<fx:Declarations>
    <!-- Place non-visual elements (e.g., services, value objects) here -->
    <fx:String id="aSimpleString"/>
</fx:Declarations>
</s:WindowedApplication>

Also calling to System.gc() did nothing, maybe the gc expects some pause in order to run.

Answer 1

The garbage collector is going to run whenever it feels like. Usually it happens on allocation of new objects but it might not happen in your case if the memory usage is not high.

You can try to call System.gc() to see if it frees those strings. But you shouldn't use that in your production code.

See this answer for more info.