I am submitting Callable objects to a ThreadPoolExecutor and they seem to be sticking around in memory.
Looking at the heap dump with the MAT tool for Eclipse see that the Callable objects are being referenced by a FutureTask$Sync's callable variable. That FutureTask$Sync is referenced by a FutureTask's sync variable. That FutureTask is referenced by the FutureTask$Sync's this$0 variable.
I have read around about this (here, here, and on SO) and it seems like the FutureTask that the callable is wrapped in upon the ThreadPoolExecutor's submit() holds a reference to the callable forever.
What I am confused about is how to ensure that the FutureTask gets garbage collected so it doesn't continue to hold the callable in memory, and hold anything the callable might be holding in memory?
Just to give more details about my particular situation, I am trying to implement the ThreadPoolExecutor in a way that allows all of the submitted tasks to be canceled if needed. I have tried several different methods I found on SO and elsewhere, such as completely shutting the executor down (with shutdown(), shutdownNow() etc) and also keeping a list of the futures return by submit() and calling cancel on all them and then clearing the list of futures. Ideally I would like not to have to shut it down, and just cancel() and clear out when needed.
All of these methods don't seem to make a difference. If I submit a callable to the pool, there is a good chance it will end