Avoiding Memory leaks by Viktor Kifer

Avoiding Memory leaks by Viktor Kifer

Transcript

1. Avoiding memory leaks
2. Memory Leak? Objects stay in memory even when they are no longer used by application
3. Detecting memory leaks
4. Symptoms • Frequent calls to GC • Lesser amount of memory reclaimed on each GC • Memory usage increases over time • as a result -> OOM and Response time decreases
5. Example 1 public class MainActivity extends AppCompatActivity implements SomeListener { protected void onCreate(Bundle savedInstanceState) { // … Singleton.getInstance().register(this); } public void onSomeEvent() { // some code here } }
6. Permanently increasing memory usage
7. Example 1 public class MainActivity extends AppCompatActivity implements SomeListener { protected void onCreate(Bundle savedInstanceState) { // ... Singleton.getInstance().register(this); } // SomeListener interface implementation protected void onDestroy() { // ... Singleton.getInstance().unregister(this); } }
8. LeakCanary https://github.com/square/leakcanary
9. Memory Dump • DDMS - “Dump HPROF file” • android.os.Debug. dumpHprofData (“filename”) %sdk%/platform-tools/ hprof-conv
10. Memory Analysis Tool
11. Preventing memory leak
12. General rules • unregister event listeners • avoid string concatenation in loops (use StringBuilder) • avoid unnecessary object creation
13. General rules (Continue) • close resources in finally blocks (Stream, Reader, Connection etc) • set static objects to null
14. General Rules (Android) • call Bitmap.recycle() • avoid object creation on onDraw() • use getApplicationContext() instead of activity context, but only when appropriate
15. References
16. Java Reference? java.lang.ref.Reference<T> • WeakReference • SoftReference • PhantomReference
17. Strong Reference Activity activity = getActivity();
18. WeakReference Reference<Activity> activityRef = new WeakReference<Activity>(getActivity()); Activity activity = activityRef.get(); if (activity != null) { // ... }
19. Non-static inner and anonymous classes contain strong reference to their outer class public class MyActivity extends Activity { // Anonymous class SomeListener contains strong reference to MyActivity instance Singleton.getInstance().addListener(new SomeListener() { // ... }); }
20. Example 2 public class HandlerLeakExampleActivity extends AppCompatActivity { private final Handler mLeakyHandler = new Handler() { @Override public void handleMessage(Message msg) { // ... } }; }
21. Example 2 public class HandlerLeakExampleActivity extends AppCompatActivity { private static class MyHandler extends Handler { private final WeakReference<HandlerLeakExampleActivity> mActivity; public MyHandler(HandlerLeakExampleActivity activity) { mActivity = new WeakReference<HandlerLeakExampleActivity>(activity); } public void handleMessage(Message msg) { HandlerLeakExampleActivity activity = mActivity.get(); if (activity != null) { // ... } } } private final MyHandler mHandler = new MyHandler(this); }
22. Q&A