I'm trying to get better at hunting down memory leaks in Android.
I will give couple of examples but first, due to the number of questions you asked that is not related to your topic
I will first explain what you see in "Instance view";
Depth: The shortest number of hops from any GC root to the selected instance.
- 0 is for "private final class" or static members
- if it's blank it's going to be reclaimed - which is harmless for you
Shallow Size: Size of this instance in Java memory
Retained Size: Size of memory that this instance dominates (as per the dominator tree).
Is it the this$0?
this$0 is a synthetic variable generated by the compiler which means "one level out of my scope", it's a parent object of a non-static inner class.
How am I supposed to tell which ones are worth investigating?
It depends, if the depth is 0 and it's your code - investigate, maybe it's a long running task with bad end condition.
When analyzing a heap dump in the Memory Profiler, you can filter profiling data that Android Studio thinks might indicate memory leaks for Activity and Fragment instances in your app.
The types of data that the filter shows include the following:
In certain situations, such as the following, the filter might yield false positives:
Filtering a heap dump for memory leaks.
![]()
Techniques for profiling your memory
While using the Memory Profiler, you should stress your app code and try forcing memory leaks.
One way to provoke memory leaks in your app is to let it run for a while before inspecting the heap.
Leaks might trickle up to the top of the allocations in the heap.
However, the smaller the leak, the longer you need to run the app in order to see it.
You can also trigger a memory leak in one of the following ways:
- Rotate the device from portrait to landscape and back again multiple times while in different activity states. Rotating the device can often cause an app to leak an Activity, Context, or View object because the system recreates the Activity and if your app holds a reference to one of those objects somewhere else, the system can't garbage collect it.
- Switch between your app and another app while in different activity states (navigate to the Home screen, then return to your app).
A growing graph is a big indicator
If you observe a trend line that only keeps going up and seldomly goes down, it could be due to a memory leak, which means some pieces of memory cannot be freed. Or there’s simply not enough memory to cope with the application. When the application has reached its memory limit and the Android OS isn’t able to allocate any more memory for the application, an OutOfMemoryError will be thrown.
Turbulence within a short period of time
Turbulence is an indicator of instability, and this applies to Android memory usage as well. When we observe this kind of pattern, usually a lot of expensive objects are created and thrown away in their short lifecycles.
The CPU is wasting a lot of cycles in performing Garbage Collection, without performing the actual work for the application. Users might experience a sluggish UI, and we should definitely optimize our memory usage in this case.
If we are talking about Java memory leaks
![enter image description here]()
public class ThreadActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_async_task);
new DownloadTask().start();
}
private class DownloadTask extends Thread {
@Override
public void run() {
SystemClock.sleep(2000 * 10);
}
}
}
Inner classes hold an implicit reference to their enclosing class, it will generate a constructor automatically and passes the activity as a reference to it.
The above code is actually
public class ThreadActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_async_task);
new DownloadTask(this).start();
}
private class DownloadTask extends Thread {
Activity activity;
public DownloadTask(Activity activity) {
this.activity = activity;
}
@Override
public void run() {
SystemClock.sleep(2000 * 10);
}
}
}
In a normal case, the user opens the activity wait 20sec until the download task is done.
When the task is done the stack released all the objects.
Then the next time the garbage collector works he will release the object from the heap.
And when the user closes the activity the main method will be released from the stack and the ThreadActivity also reclaimed from the heap and everything works as needed without leaks.
In a case that the user closes/rotate the activity after 10sec.
The task is still working that means the reference for the activity still alive and we have a memory leak 💣
Note: when the download run() task is done the stack release the objects. so when the garbage collector works next time the objects will be reclaimed from the heap because there is no object referenced on it.
related Youtube playlist
And https://square.github.io/leakcanary/fundamentals/ is great.
