Excessive connection latency... Does Adobe Air support connection pooling on mobile?

Question

Hello,
I am developing a mobile app which loads thumbnail images from a remote server. During testing on the Android platform, however, I have discovered that images are very slow to load. By monitoring server logs I have determined that the poor performance is caused by the lack of connection pooling, meaning that each request builds a new connection. Running the sample code below on a mobile device produces 20 requests and 20 connection attempts. By comparison, the same web or desktop app creates 2 connections and reuses those connections for subsequent requests. The substantial overhead and latency associated with generating new connections has a substantial affect on performance, with 20 thumbnails taking approximately 4-5 seconds to load on mobile versus 0.5 - 1 second on a desktop.
I have included a sample app below to emphasis the performance issue. The image itself is very small (290 bytes) to focus the issue on connection latency. I have confirmed this behavior on numerous Android devices, running 4.1, 4.0, and 2.3. I have also attempted using Loader v. URLLoader v. URLStream and sequential v. simultaneous loading with no change in connection behavior. Attempting to set the connection to 'keep-alive' in the URLRequest also has no affect.
package
          import flash.display.Loader;
          import flash.display.Sprite;
          import flash.display.StageAlign;
          import flash.display.StageScaleMode;
          import flash.events.Event;
          import flash.net.URLRequest;
          import flash.utils.getTimer;
          public class Main extends Sprite
                    private var _count:int = 0;
                    public function Main()
                              super();
                              stage.align = StageAlign.TOP_LEFT;
                              stage.scaleMode = StageScaleMode.NO_SCALE;
                              trace("Start time " + getTimer() + " ms");
                              var loader:Loader;
                              var url:String = "http://fbcdn-profile-a.akamaihd.net/static-ak/rsrc.php/v2/yo/r/UlIqmHJn-SK.gif";  // 290 bytes
                              for (var i:int = 0; i < 20; i++) {
                                        loader = this.addChild(new Loader()) as Loader;
                                        loader.contentLoaderInfo.addEventListener(Event.COMPLETE, complete);
                                        loader.load(new URLRequest(url));
                    private function complete(event:Event):void
                              _count++
                              trace("Finished " + _count + " at " + getTimer() + " ms");
So, I have a couple questions:
1) Is there something that I can do to enable connection reuse?
2) Is this an inherent limitation with Adobe Air for mobile?
3) Can someone confirm whether this limitation exists on other mobile platforms (iOS or Blackberry)?
Any help that you can provide would be greatly appreciated. I am really hoping that this isn't a fundamental limitation of Adobe Air as it causes my app to feel very sluggish.
Thanks,
Adam

Answer 1

Hmm. You were absolutely correct, that's a bit disappointing!
This is Android recompiled for 3.4 rather than 3.1.
null
COMPLETED 50 with 8 loaders in 11327 milliseconds or 226.54 per load.   50           8              11327    226.54
COMPLETED 50 with 50 loaders in 8899 milliseconds or 177.98 per load.   50           50           8899       177.98
COMPLETED 50 with 50 loaders in 9280 milliseconds or 185.6 per load.     50           50           9280       185.6
COMPLETED 50 with 50 loaders in 9513 milliseconds or 190.26 per load.   50           50           9513       190.26
COMPLETED 50 with 8 loaders in 9744 milliseconds or 194.88 per load.     50           8              9744       194.88
COMPLETED 50 with 1 loaders in 16383 milliseconds or 327.66 per load.   50           1              16383    327.66
Versus Apple iPad recompiled for 3.4 rather than 3.1.
null
COMPLETED 50 with 8 loaders in 502 milliseconds or 10.04 per load. 50      8        502    10.04
COMPLETED 50 with 50 loaders in 100 milliseconds or 2 per load.     50      50      100    2
COMPLETED 50 with 50 loaders in 117 milliseconds or 2.34 per load. 50      50      117    2.34
COMPLETED 50 with 50 loaders in 93 milliseconds or 1.86 per load.  50      50      93      1.86
COMPLETED 50 with 8 loaders in 270 milliseconds or 5.4 per load.    50      8        270    5.4
COMPLETED 50 with 8 loaders in 307 milliseconds or 6.14 per load.  50      8        307    6.14
COMPLETED 50 with 8 loaders in 316 milliseconds or 6.32 per load.  50      8        316    6.32
COMPLETED 50 with 4 loaders in 555 milliseconds or 11.1 per load.  50      4        555    11.1
COMPLETED 50 with 4 loaders in 547 milliseconds or 10.94 per load. 50      4        547    10.94
COMPLETED 50 with 4 loaders in 535 milliseconds or 10.7 per load.  50      4        535    10.7
COMPLETED 50 with 2 loaders in 1038 milliseconds or 20.76 per load.        50      2        1038          20.76
COMPLETED 50 with 2 loaders in 1042 milliseconds or 20.84 per load.        50      2        1042          20.84
COMPLETED 50 with 1 loaders in 2107 milliseconds or 42.14 per load.        50      1        2107          42.14
COMPLETED 50 with 1 loaders in 2099 milliseconds or 41.98 per load.        50      1        2099          41.98
Both are on release compile, which should take out all of the variability. So, yes, it looks as if the 3.4 AIR runtime has lost the connection pooling but ONLY for Android.
PS: Code I used in my test (which was a conventional View based Mobile app) is below in case you want to include it when you submit a bug report.
<?xml version="1.0" encoding="utf-8"?>
<s:View xmlns:fx="http://ns.adobe.com/mxml/2009"
  xmlns:s="library://ns.adobe.com/flex/spark" title="TestLLatency" xmlns:mx="library://ns.adobe.com/flex/mx">
<fx:Script>
  <![CDATA[
   import mx.events.FlexEvent;
   protected function uicomponent1_creationCompleteHandler(event:FlexEvent):void
    startTest();
   public function startTest():void {
    if(queue) throw new Error("Please wait for previous test to end.");
    queue = new Array();
    _count = 0;
    var loader:Loader;
    var i:int;
    for (i = 0; i < numToQueue; i++) {
     loader = bob.addChild(new Loader()) as Loader;
     loader.x = (i%10)*50;
     loader.y = Math.floor(i/5)*50;
     loader.contentLoaderInfo.addEventListener(Event.COMPLETE, complete);
     queue.push(loader);
    startTime = getTimer();
    for(i=0;i<numLoaders;i++) {
     nextQueue();
   protected var startTime:int;
   protected var endTime:int;
   protected var numToQueue:int = 50;
   protected var numLoaders:int = 8;
   protected var queue:Array;
   private var _count:int;
   private function complete(event:Event):void
    _count++
    nextQueue();
   [Bindable] protected var results:String;
   protected function nextQueue():void {
    var url:String = "http://fbcdn-profile-a.akamaihd.net/static-ak/rsrc.php/v2/yo/r/UlIqmHJn-SK.gif";  // 290 bytes
    if(queue && queue.length) {
     var loader:Loader = queue.pop() as Loader;
     loader.load(new URLRequest(url));
    } else if(_count==numToQueue) {
     endTime = getTimer();
     var elapsed:int = endTime-startTime;
     results += "\n"+("COMPLETED "+numToQueue+" with "+numLoaders+" loaders in "+(elapsed)+" milliseconds or "+(elapsed/numToQueue)+" per load.\t"+[numToQueue,numLoaders,elapsed,elapsed/numToQueue].join("\t"));
     queue = null;
     while(bob.numChildren>5) {
      bob.removeChildAt(bob.numChildren-1);
     bob.getChildAt(0).addEventListener(MouseEvent.CLICK,repeatTest);
     bob.getChildAt(1).addEventListener(MouseEvent.CLICK,repeatTest);
     bob.getChildAt(2).addEventListener(MouseEvent.CLICK,repeatTest);
     bob.getChildAt(3).addEventListener(MouseEvent.CLICK,repeatTest);
     bob.getChildAt(4).addEventListener(MouseEvent.CLICK,repeatTest);
   protected function repeatTest(event:MouseEvent):void {
    var dob:DisplayObject = event.target as DisplayObject;
    var testBehaviour:int = dob.parent.getChildIndex(dob);
    try {
     switch(testBehaviour) {
      case 4 :
       this.numLoaders = this.numToQueue;
       break;
      case 3 :
       this.numLoaders = 8;
       break;
      case 2 :
       this.numLoaders = 4;
       break;
      case 1 :
       this.numLoaders = 2;
       break;
      case 0 :
       this.numLoaders = 1;
       break;
     startTest();
     dob.removeEventListener(MouseEvent.CLICK,repeatTest);
     for(var i:int=0;i<5;i++) bob.removeChildAt(0);
    } catch(e:Error) {
     trace(e.message); 
  ]]>
</fx:Script>
<fx:Declarations>
  <!-- Place non-visual elements (e.g., services, value objects) here -->
</fx:Declarations>
<s:HGroup width="100%" height="100%">
  <mx:UIComponent id="bob" width="100%" height="100%" creationComplete="uicomponent1_creationCompleteHandler(event)" />
  <s:TextArea text="{results}" width="100%" height="100%" />
</s:HGroup>
</s:View>