Android: AlertDialog causes a memory leak

Question

My application shows an AlertDialog with a ListView inside. Everything worked fine bun then I decided to test this for memory leaks. After running the app for some time I opened MAT and generated Leak Suspects report. MAT found several similar leaks:

One instance of "com.android.internal.app.AlertController$RecycleListView" loaded by "<system class loader>" occupies ...

I spent a lot of time searching for the reason of this leak. Code review didn't help me and I started googling. That's what I found:

Issue 5054: AlertDialog seems to cause a memory leak through a Message in the MessageQueue

I decided to check whether this bug reproduces or not. For this purpose I created a little program which consists of two activities. MainActivity is an enrty point. It contains only a buttons which runs LeakedActivity. The latter just shows an AlertDialog in its onCreate() method. Here's the code:

public class MainActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        findViewById(R.id.button).setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(
                    new Intent(MainActivity.this, LeakedActivity.class));
            }
        });
    }
}

public class LeakedActivity extends Activity {
    private static final int DIALOG_LEAK = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        if (savedInstanceState == null) {
            showDialog(DIALOG_LEAK);
        }
    }

    @Override
    protected Dialog onCreateDialog(int id) {
        if (id == DIALOG_LEAK) {
            return new AlertDialog.Builder(this)
                .setTitle("Title")
                .setItems(new CharSequence[] { "1", "2" },
                    new OnClickListener() {
                        private final byte[] junk = new byte[10*1024*1024];

                        @Override
                        public void onClick(DialogInterface dialog, int which) {
                            // nothing
                        }
                    })
                .create();
        }
        return super.onCreateDialog(id);
    }
}

MAT reports this application leaks com.android.internal.app.AlertController$RecycleListView every time the AlertDialog is dismissed and the LeakedActivity is finished.

I can't find any error in this small program. It looks like a very simple case of using AlertDialog and it must work well but seems it doesn't. So I'd like to know how to avoid memory leaks when using AlertDialogs with items. And why hasn't this problem been fixed yet? Thanks in advance.

Answer 1

Cannot reproduce for Android 2.3.4 2.3.3. I Tested your exact code on a actual device and from what I see in LogCat, the heap size stays constant over time. Sadly I was not able to hprof-conf my dumps (ERROR: expecting 1.0.3)

08-19 08:41:58.026: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 13K, 50% free 2698K/5379K, external 83K/519K, paused 16ms
08-19 08:41:58.056: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1K, 43% free 3720K/6471K, external 83K/519K, paused 18ms
08-19 08:45:30.113: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1076K, 58% free 2723K/6471K, external 595K/1042K, paused 18ms
08-19 08:45:30.143: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 6K, 43% free 3740K/6471K, external 507K/1019K, paused 19ms
08-19 08:45:35.869: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1087K, 58% free 2726K/6471K, external 595K/1019K, paused 18ms
08-19 08:45:35.899: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 6K, 43% free 3744K/6471K, external 552K/1019K, paused 18ms
08-19 08:45:39.112: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1077K, 58% free 2734K/6471K, external 595K/1019K, paused 17ms
08-19 08:45:39.152: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 6K, 43% free 3752K/6471K, external 530K/1019K, paused 20ms
08-19 08:46:14.186: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1089K, 58% free 2736K/6471K, external 595K/1019K, paused 23ms
08-19 08:46:14.216: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 4K, 42% free 3755K/6471K, external 552K/1019K, paused 21ms
08-19 08:46:16.519: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1092K, 58% free 2736K/6471K, external 595K/1019K, paused 23ms
08-19 08:46:16.549: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 6K, 42% free 3753K/6471K, external 530K/1019K, paused 22ms
08-19 08:47:15.686: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1089K, 58% free 2736K/6471K, external 595K/1019K, paused 18ms
08-19 08:47:15.716: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 3K, 42% free 3756K/6471K, external 561K/1019K, paused 18ms
08-19 08:48:01.391: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1077K, 58% free 2736K/6471K, external 595K/1019K, paused 19ms
08-19 08:48:01.421: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 6K, 43% free 3753K/6471K, external 530K/1019K, paused 19ms
08-19 08:48:09.409: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1089K, 58% free 2737K/6471K, external 758K/1019K, paused 18ms
08-19 08:48:09.449: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 4K, 42% free 3756K/6471K, external 561K/1019K, paused 21ms
08-19 08:48:11.771: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1076K, 58% free 2736K/6471K, external 595K/1019K, paused 18ms
08-19 08:48:11.811: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 6K, 42% free 3754K/6471K, external 530K/1019K, paused 20ms
08-19 08:48:13.653: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1089K, 58% free 2737K/6471K, external 595K/1019K, paused 18ms
08-19 08:48:13.683: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 3K, 42% free 3758K/6471K, external 561K/1019K, paused 19ms
08-19 08:48:15.785: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1077K, 58% free 2736K/6471K, external 595K/1019K, paused 18ms
08-19 08:48:15.825: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 6K, 42% free 3754K/6471K, external 530K/1019K, paused 19ms
08-19 08:48:18.227: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1088K, 58% free 2737K/6471K, external 595K/1019K, paused 19ms
08-19 08:48:18.257: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 4K, 42% free 3756K/6471K, external 552K/1019K, paused 20ms
08-19 08:49:06.575: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1075K, 58% free 2736K/6471K, external 595K/1019K, paused 18ms
08-19 08:49:06.605: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 6K, 42% free 3754K/6471K, external 530K/1019K, paused 17ms
08-19 08:49:09.668: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1097K, 58% free 2729K/6471K, external 595K/1019K, paused 18ms
08-19 08:49:09.708: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 4K, 43% free 3748K/6471K, external 552K/1019K, paused 20ms
08-19 08:49:12.440: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1077K, 58% free 2736K/6471K, external 595K/1019K, paused 18ms
08-19 08:49:12.470: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 6K, 43% free 3753K/6471K, external 530K/1019K, paused 17ms
08-19 08:49:15.473: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1088K, 58% free 2736K/6471K, external 595K/1019K, paused 18ms
08-19 08:49:15.503: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 4K, 42% free 3756K/6471K, external 561K/1019K, paused 17ms
08-19 08:49:18.476: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1091K, 58% free 2737K/6471K, external 595K/1019K, paused 18ms
08-19 08:49:18.506: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 6K, 42% free 3754K/6471K, external 507K/1019K, paused 20ms
08-19 08:49:21.289: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1090K, 58% free 2737K/6471K, external 595K/1019K, paused 18ms
08-19 08:49:21.319: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 6K, 42% free 3754K/6471K, external 484K/996K, paused 20ms
08-19 08:51:43.307: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1071K, 58% free 2723K/6471K, external 595K/996K, paused 17ms
08-19 08:51:43.338: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed <1K, 43% free 3747K/6471K, external 595K/996K, paused 20ms
08-19 08:51:45.620: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1086K, 58% free 2729K/6471K, external 595K/974K, paused 18ms
08-19 08:51:45.660: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 7K, 43% free 3745K/6471K, external 462K/974K, paused 20ms
08-19 08:51:47.421: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1080K, 58% free 2738K/6471K, external 595K/974K, paused 17ms
08-19 08:51:47.452: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 6K, 42% free 3755K/6471K, external 484K/974K, paused 19ms
08-19 08:52:56.949: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 27K, 58% free 2733K/6471K, external 83K/595K, paused 18ms
08-19 08:52:56.979: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed <1K, 42% free 3757K/6471K, external 83K/595K, paused 17ms
08-19 08:53:01.233: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1072K, 58% free 2727K/6471K, external 595K/1107K, paused 18ms
08-19 08:53:01.274: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 2K, 43% free 3749K/6471K, external 578K/1090K, paused 20ms
08-19 08:53:04.046: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1081K, 58% free 2740K/6471K, external 595K/1064K, paused 18ms
08-19 08:53:04.086: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 6K, 42% free 3758K/6471K, external 530K/1042K, paused 20ms
08-19 08:53:25.948: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1090K, 58% free 2740K/6471K, external 595K/1042K, paused 19ms
08-19 08:53:25.978: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 6K, 42% free 3758K/6471K, external 552K/1042K, paused 19ms
08-19 08:57:51.246: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1099K, 58% free 2753K/6471K, external 595K/1042K, paused 18ms
08-19 08:57:51.286: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 13K, 42% free 3764K/6471K, external 561K/1042K, paused 20ms
08-19 09:00:47.699: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1106K, 58% free 2731K/6471K, external 595K/1019K, paused 18ms
08-19 09:00:47.729: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 7K, 43% free 3748K/6471K, external 484K/996K, paused 17ms
08-19 09:00:56.817: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1080K, 58% free 2741K/6471K, external 595K/996K, paused 18ms
08-19 09:00:56.848: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 6K, 42% free 3758K/6471K, external 530K/996K, paused 23ms
08-19 09:01:00.701: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1077K, 58% free 2739K/6471K, external 595K/996K, paused 19ms
08-19 09:01:00.731: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 6K, 42% free 3756K/6471K, external 530K/996K, paused 22ms
08-19 09:01:25.916: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 1077K, 58% free 2739K/6471K, external 595K/996K, paused 18ms
08-19 09:01:25.946: DEBUG/dalvikvm(3510): GC_FOR_MALLOC freed 6K, 42% free 3756K/6471K, external 530K/996K, paused 20ms

Answer 2

(2/12/2012): see UPDATE below.

This problem is not actually caused by the AlertDialog but more related to the ListView. You can reproduce the same problem by using the following activity:

public class LeakedListActivity extends ListActivity {
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // Use an existing ListAdapter that will map an array
    // of strings to TextViews
    setListAdapter(new ArrayAdapter<String>(this,
            android.R.layout.simple_list_item_1, mStrings));
    getListView().setOnItemClickListener(new OnItemClickListener() {
        private final byte[] junk = new byte[10*1024*1024];
        @Override
        public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,
                long arg3) {
        }
    });     
}
    private String[] mStrings = new String[] {"1", "2"};
}

Rotate the device several times, and you'll get OOM.

I haven't got the time to investigate more on what is the real cause (I know what's happening but not clear why it's happening; can be bug, or designed). But here's one workaround that you can do, at least to avoid the OOM in your case.

First, you'll need to keep a reference to your leaked AlertDialog. You can do this in the onCreateDialog(). When you're using setItems(), the AlertDialog will internally create a ListView. And when you set the onClickListener() in your setItems() call, internally it will be assigned to the ListView onItemClickListener().

Then, in the leaked activity's onDestroy(), set the AlertDialog's ListView's onItemClickListener() to null, which will release the reference to the listener an make whatever memory allocated within that listener to be eligible for GC. This way you won't get OOM. It's just a workaround and the real solution should actually be incorporated in the ListView.

Here's a sample code for your onDestroy():

@Override
protected void onDestroy() {
    super.onDestroy();
    if(leakedDialog != null) {
            ListView lv = leakedDialog.getListView();
            if(lv != null)  lv.setOnItemClickListener(null);
    }
}

UPDATE (2/12/2012): After further investigation, this problem is actually not particularly related to ListView nor to OnItemClickListener, but to the fact that GC doesn't happen immediately and need time to decide which objects are eligible and ready for GC. Try this:

public class MainActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        // this will create reference from button to 
        // the listener which in turn will create the "junk"
        findViewById(R.id.button).setOnClickListener(new View.OnClickListener() {
            private byte[] junk = new byte[10*1024*1024];
            @Override
            public void onClick(View v) {
                // do nothing
            }
        });
    }
}

Rotate a couple of times, and you'll get the OOM. The problem is after you rotate, the junk is still retained because GC hasn't and can't happen yet (if you use MAT, you'll see that this junk is still retained by the button's listener deep down from the GCroot, and it will take time for the GC to decide whether this junk is eligible and can be GCed.) But at the same time, a new junk needs to be created after the rotation, and because of the mem alloc size (10M per junk), this will cause OOM.

The solution is to break any references to the listener (the junkowner), in this case from the button, which practically makes the listener as a GCroot with only short path to the junk and make the GC decide faster to reclaim the junk memory. This can be done in the onDestroy():

@Override
protected void onDestroy() {
    // this will break the reference from the button
    // to the listener (the "junk" owner)
    findViewById(R.id.button).setOnClickListener(null);
    super.onDestroy();
}