How to ensure garbage collection of a FutureTask that is submitted to a ThreadPoolExecutor?
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][1], [here][2], 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 up sticking around.

What am I doing wrong?

Thanks.


  [1]: http://stochastyk.blogspot.com/2006/12/memory-issues-using-java.html
  [2]: http://markmail.org/message/3r3z6oxjkkiimjn6#query:+page:1+mid:45ouqntsrs72hyn6+state:results
How to ensure garbage collection of a FutureTask that is submitted to a ThreadPoolExecutor?
===

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][1], [here][2], 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 up sticking around.

What am I doing wrong?

Thanks.


  [1]: http://stochastyk.blogspot.com/2006/12/memory-issues-using-java.html
  [2]: http://markmail.org/message/3r3z6oxjkkiimjn6#query:+page:1+mid:45ouqntsrs72hyn6+state:results