Debugging memory leaks in the IBEX GUI

Debugging memory leaks in the IBEX GUI

Symptoms

• Java memory leaks cause high CPU usage rather than the more intuitive high memory usage. The IBEX GUI is limited to a heap size of 500MB by default. When the heap gets close to it's maximum size, the garbage collector goes crazy trying to recover memory wherever it can, and therefore uses a lot of CPU.

• Because of the high CPU usage, the GUI will feel slow and sluggish.

• When there is no more memory available, java will crash with an OutOfMemoryException. Note that this exception might not occur on the GUI thread, and therefore various components running in separate threads might fail before the GUI crashes.

Tools

• Java visual VM (C:\Program Files\Java\jdk1.8.0_73\bin\jvisualvm.exe for example)

• Eclipse debugger

• A way to reproduce the issue

Setup

• In the java visual VM, on the left, you should see an Eclipse (pid xxxx) process. This is either your Eclipse IDE or IBEX. If you're unsure which is which, look under "Threads" for anything to do with ActiveMQ: This will be IBEX.

• Reproduce your issue, looking at the heap usage in the java visual vm.

• A healthy GUI will show heap usage fluctuating quite a lot on a short-term basis, but with no long-term trend.

• A GUI with a memory leak will also fluctuate in the short term, but will also have a long term trend upwards while the issue is being reproduced.

Diagnosis

• Go under Sampler -> Memory and look at which objects are using up a lot of heap space. Note that this is only the object, not any of the objects that it owns!

public class MemoryLeak{
     RealMemoryLeak thisThingIsReallyBig = reallyBig; // Something enormous
}

will not make MemoryLeak show up as a large object!

• Under "monitor" you can create a Heap Dump. This is a file with information about all the objects that were loaded at the time. You might find this useful or not depending on your problem.

• Don't bother trying to "compute retained sizes": The IBEX program is too large and will cause the profiler itself to crash with an OutOfMemoryException.