Android - recover from low memory condition

Question

I'm developing an application with very intense image processing where I have multiple ListFragments in the horizontal FragmentStatePagerAdapter. I aggressively employ practically every trick and suggestion I was able to find here and elsewhere. I download bitmaps and save these to SD and as soft reference memory cache.

Nevertheless as I use the app at certain point I start seeing messages in LogCat just like one below

11-05 15:57:43.951: I/dalvikvm-heap(5449): Clamp target GC heap from 32.655MB to 32.000MB
11-05 15:57:43.951: D/dalvikvm(5449): GC_FOR_MALLOC freed 0K, 24% free 11512K/14983K, external 17446K/17896K, paused 64ms
11-05 15:57:44.041: D/dalvikvm(5449): GC_EXTERNAL_ALLOC freed <1K, 24% free 11511K/14983K, external 17258K/17896K, paused 77ms

If I continue, messages above will become more urgent

11-05 16:02:09.590: D/dalvikvm(5449): GC_FOR_MALLOC freed 0K, 23% free 11872K/15239K, external 17497K/17896K, paused 71ms
11-05 16:02:09.700: D/dalvikvm(5449): GC_EXTERNAL_ALLOC freed <1K, 23% free 11872K/15239K, external 17497K/17896K, paused 84ms
11-05 16:02:09.720: E/dalvikvm-heap(5449): 192816-byte external allocation too large for this process.
11-05 16:02:09.800: I/dalvikvm-heap(5449): Clamp target GC heap from 33.057MB to 32.000MB
11-05 16:02:09.800: D/dalvikvm(5449): GC_FOR_MALLOC freed 0K, 23% free 11872K/15239K, external 17497K/17896K, paused 68ms
11-05 16:02:09.800: E/GraphicsJNI(5449): VM won't let us allocate 192816 bytes

And inevitably the app will crash with OutOfMemoryException The symptoms are classical memory leak. Yet in my Fragment#onDestroy method I cancel all the pending tasks, unbind and nullify the views and call Bitmap#recycle. Interestingly enough, I do see GC calls in the LogCat but even if I pause for extended period the memory is never reclaimed.

My gut feeling is that it is continuous re-reading of images from SD that causes degradation and inevitable demise

Here's utility cleaning method I'm using trying to shake off drawables (there's more as I said to cancel pending/running tasks and empty ListView adapters)

public static void unbindDrawables(View view, final boolean agressive) {
        if (view instanceof ViewGroup) {
            for (int i = 0; i < ((ViewGroup) view).getChildCount(); i++) {
                unbindDrawables(((ViewGroup) view).getChildAt(i), agressive);
            }
            if (!AdapterView.class.isInstance(view)) {
                ((ViewGroup) view).removeAllViews();
            }
        } else {
            Drawable bmp = view.getBackground();
            if (bmp == null && ImageView.class.isInstance(view)) bmp = ((ImageView) view).getDrawable();
            if (bmp != null) {
                bmp.setCallback(null);
                if (agressive && (TaggedDrawable.class.isInstance(bmp))) {
                    Bitmap bm = ((BitmapDrawable) bmp).getBitmap();
                    if (bm != null) {
                        if (DEBUG) Log.i(TAG, "Forcing bitmap recycle for " + bmp);
                        bm.recycle();
                        bm = null;
                        view.destroyDrawingCache();
                        view = null;
                    }
                }
            }
        }
    }

Needless to say I'm seriously disturbed at this point and will greatly appreciate any suggestions

Answer 1

First,GC will not recycle the memory at once you called. Here are some advice from android developer website:

1. Do not keep long-lived references to a context-activity (a reference to an activity should have the same life cycle as the activity itself)

2. Try using the context-application instead of a context-activity

3. Avoid non-static inner classes in an activity if you don't control their life cycle, use a static inner class and make a weak reference to the activity inside. The solution to this issue is to use a static inner class with a WeakReference to the outer class, as done in ViewRoot and its W inner class for instance

4. A garbage collector is not an insurance against memory leaks

Second, try to use BitmapFactory.options when you do not very care the quality of the bitmap.

Third, use try catch to process the OutOfMemory exception in catch block.

Finally, Use Memory Analyzer . Open DDMS in Eclipse, in the toolbar there is a update heap button. you can use this to generate a hprof file, then use hprof-conv tool in your andorid-sdk-tools directory to convert the file to the specified format file that Memory Analyzer can read. Now you can use the Memory Analyzer to analysis the possible memory leak. It's really a good tool that will give you many suggestions to avoid outofmemory.

Hope this will help you, If you find some better methods please tell me, i also face the outofmemory in my app.