Question

This is simple test on AS3 for BitmapData memory allocation.

private function memoryTest(): void
{
  trace("BitmapData memory test. Create bmps..."); // First breakpoint
  var bmps:Array = new Array (1000);

  for (var i:int=0; i<1000; i++)
  {
    bmps[i] = new BitmapData(451, 451, true, 0);
    trace(i+". bmp created");
  }

  trace("All bmps created."); // Second breakpoint

  for (i=0; i<1000; i++)
  {
    bmps[i].dispose();
    bmps[i] = null;
  }
  bmps.splice(0, bmps.length);
  bmps = null;

  freeMemoryGC();

  trace("All bmps deleted.");
  trace("Test complete."); // Last breakpoint
}

private function freeMemoryGC(): void
{
  // the GC will perform a full mark/sweep on the second call.
  try
  {
    new LocalConnection().connect('foo');
    new LocalConnection().connect('foo');
  }
  catch (e:*)
  {
  }

  System.gc();
  System.gc();
}

There are 3 breakpoints in this test, that are commented in code. Breakpoints pause program during some time. Breakpoints correspond to the horizontal lines on this memory state chart.

My question is: why not all memory was free after dispose() calls? What wrong in this code and how to clear BitmapData objects properly?

UPDATE 1:
I don’t think that problem is in garbage collector. dispose() works out of GC and it should release the pixels data. Also this example should allocate 451*451*4*1000 bytes theoretically. But this test application allocates 25% more bytes in System.privateMemory and these 25% is never released by GC and dispose().

UPDATE 2:
If I create 13 images 4059×4059 px instead of 100 images 451×451 px, then memory allocates exactly equals to theoretical size and memory is released properly after call GC! I don’t know why it happens.

UPDATE3:
Here is my results of interval test, created by Daniel MesSer in him answer:

Answer 1

Try and remove the thing about local connection in free memorygc-function. Does that solve it?

EDIT:

package nyx_gaming_group.as3_tests {
import flash.display.BitmapData;
import flash.display.Sprite;
import flash.system.System;
import messer_entertainment.MesSerUtils;

/**
 * ...
 * @author Daniel Dahlkvist
 */
public class BitmapDataMemoryLeak extends Sprite {
    private var _bitmaps:Array;

    public function BitmapDataMemoryLeak() {
        run();
    }

    private function run():void {
        MesSerUtils.delayCall(createBitmaps, 150);
        MesSerUtils.delayCall(destroyBitmaps, 4500);
        MesSerUtils.delayCall(freeMemoryGC, 4700);
        MesSerUtils.delayCall(run, 8000);
    }

    private function createBitmaps():void {
        trace("BitmapData memory test. Create bmps..."); // First breakpoint
        _bitmaps = new Array(1000);

        for (var i:int = 0; i < 1000; i++) {
            _bitmaps[i] = new BitmapData(451, 451, true, 0);
        }

        trace("All bmps created."); // Second breakpoint            
    }

    private function destroyBitmaps():void {
        for (var i:int = 0; i < _bitmaps.length; i++) {
            _bitmaps[i].dispose();
            _bitmaps[i] = null;
        }
        _bitmaps = null;

        trace("All bmps deleted.");
        trace("Test complete."); // Last breakpoint
    }

    private function freeMemoryGC():void {
        System.gc();
    }
}
}