如何确保提交给ThreadPoolExecutor然后取消的FutureTask的垃圾回收？(How to ensure garbage collection of a FutureTask that is submitted to a ThreadPoolExecutor and then cancelled?)

 我将Callable对象提交给一个ThreadPoolExecutor ，它们似乎在内存中存在。 
 
 查看带有用于Eclipse的MAT工具的堆转储，看到可调对象被FutureTask$Sync的可调用变量引用。 FutureTask$Sync由FutureTask的同步变量引用。 该FutureTask由FutureTask$Sync的$ 0变量引用。 
 
 我已经阅读了关于这个（ 这里 ， 在这里 ，以及所以），并且它看起来像FutureTask ，可调用包装在ThreadPoolExecutor的submit（）持有永久可调用的引用。 
 
 我感到困惑的是如何确保FutureTask得到垃圾收集，因此它不会继续在内存中保存可调用对象，并且保存可调用对象可能在内存中保留的任何内容？ 
 
 只是为了提供有关我的特定情况的更多细节，我试图以允许所有提交的任务在需要时被取消的方式实现ThreadPoolExecutor 。 我尝试了几种不同的方法，我在SO和其他地方找到了一些方法，例如完全关闭执行程序（使用shutdown() ， shutdownNow()等），并通过submit()和调用cancel来保存期货的列表然后清除期货清单。 理想情况下，我不想关闭它，只需cancel()并在需要时清除。 
 
 所有这些方法似乎都没有区别。 如果我向池中提交一个可调用的函数，那么它很可能会结束。 
 
 我究竟做错了什么？ 
 
 谢谢。 
 
 编辑： 
 
 按照要求，这是ThreadPoolExecutor的构造函数。 
 
public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
    super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
}
 
 进一步测试后，我可以看到，如果我让已提交给ThreadPoolExecutor的任务完成，那么就没有泄漏。 如果我尝试取消它们，例如： 
 
shutdownNow()
 
 或者保存对未来的引用并稍后调用cancel： 
 
Future referenceToCancelLater = submit(task);
...
referenceToCancelLater.cancel(false);
 
 或者使用如下方法将它们从队列中删除： 
 
getQueue.drainTo(someList)
 
 要么 
 
getQueue.clear()
 
 或循环保存期货和电话的参考： 
 
getQueue.remove(task)
 
 如上所述，任何这些情况都会导致FutureTask停滞不前。 
 
 所以真正的问题是如何正确地取消或移除ThreadPoolExecutor中的项目，以便FutureTask被垃圾回收并且不会永远泄漏？ 

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 up sticking around.
 
What am I doing wrong?
 
Thanks.
 
Edit:
 
As requested, here is the constructor for the ThreadPoolExecutor.
 
public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) {
    super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
}
 
After further testing I can see that if I let the tasks that have been submitted to the ThreadPoolExecutor finish, then there is no leak. If I try to cancel them in anyway such as:
 
shutdownNow()
 
Or saving a reference to the future and calling cancel on it later:
 
Future referenceToCancelLater = submit(task);
...
referenceToCancelLater.cancel(false);
 
Or by removing them from the queue with methods like:
 
getQueue.drainTo(someList)
 
or
 
getQueue.clear()
 
or Looping through saved references to the futures and calling:
 
getQueue.remove(task)
 
Any of those cases causes the FutureTask to stick around as described above.
 
So the real question in all of this is how to I properly cancel or remove items from a ThreadPoolExecutor so that the FutureTask is garbage collected and not leaked forever?

原文：https://stackoverflow.com/questions/4917039