What is leaking int arrays in my program?

I have Java program that, over about 16 hours, is slowly filling the heap with integer arrays that the GC is not getting rid of.

I only have VisualVM available to diagnose the problem, which is how I found that it’s int[] that is filling the heap.

Any ideas how I can find the source of the int[] creation?

I’m new to using the profiler so maybe I missed that function but I’ve used it’s heap dump, snapshot, and profiler to look at this and all it’s telling me is that int[] is in high use.

Answer

In VisualVM you can find the references to objects. This should give you a clue about what part of your program that is leaking those int arrays.

Instructions:

1. Let your program run for a long time, so that there are many leaked int array instances on the heap for you to find.

2. Make a heap dump in VisualVM: Main menu > Applications > Heap Dump. A heap dump tab should open.

3. In the heap dump tab, click the Summary field and change it to Objects. A list of the types of heap objects should open.

4. Expand the int[] entry to see a list of instances.

5. Expand one of the instances.

6. Expand the references entry.

A list of fields with references to that int array instance will open. The information here might give you a clue.

Repeat step 5-6 for different instances until you find one of the leaked arrays.

The following image shows the references to an int array in a heap dump of my Eclipse.

In this example the int array instance was stored in the valueTable field of some internal Eclipse OffsetTable class, which in turn was used by a RegistryObjectManager.