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Groups > comp.lang.java.programmer > #14839

Re: Proposed new Java feature

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"Eric Sosman" <esosman@ieee-dot-org.invalid> wrote in message 
news:jptvdf$1s5$1@dont-email.me...
> On 5/27/2012 3:04 PM, Mike Schilling wrote:
>> "Daniel Pitts"<newsgroup.nospam@virtualinfinity.net>  wrote in message
>> news:8Euwr.47425$On2.20024@newsfe16.iad...
>>> On 5/27/12 11:00 AM, Mike Schilling wrote:
>>>> "markspace"<-@.>   wrote in message news:jptkmp$vbg$1@dont-email.me...
>>>>> On 5/26/2012 4:11 PM, Mike Schilling wrote:
>>>>>
>>>>>> Proposed feature: a static method on Thread that clears all
>>>>>> ThreadLocals
>>>>>> for
>>>>>> the current thread.
>>>>>>
>>>>>
>>>>>
>>>>> I can see your points.  However, I don't have any real experience with
>>>>> ThreadLocal, and when a neophyte agrees with your argument, that's a 
>>>>> red
>>>>> flag.
>>>>>
>>>>> Here's a blog where someone seems to have the same issue as you.
>>>>>
>>>>> <http://weblogs.java.net/blog/jjviana/archive/2010/06/10/threadlocal-thread-pool-bad-idea-or-dealing-apparent-glassfish-memor>
>>>>>
>>>>> At the end of the comments, there's a suggestion to use
>>>>> ThreadLocal::remove(), with the implication that it allows the thread
>>>>> local variable to be garbage collection.  Is there a reason that 
>>>>> doesn't
>>>>> work for you?
>>>>
>>>> That acts on an individual ThreadLocal (and works quite well), but it
>>>> doens't allow removing all ThreadLocals that might have been 
>>>> accumlated.
>>> You're basically saying "This type of resource can leak if not cleared
>>> appropriately, so there should be a 'Release all resources' method."
>>>
>>> When paraphrased that way, does that make it clearer why it isn't a good
>>> idea? It would be about the same as a "File.closeAll()" or a
>>> "Socket.closeAll()" call.  Extremely dangerous and only a crutch for not
>>> doing the right thing to begin with.
>>
>> Or a "collect all unused memory" call . Clearly, that's a crutch for not
>> keeping track of memory allocation properly in the first place.  And the
>> fact that files and sockets are closed when a process exits is yet 
>> another
>> crutch.
>
>     I'm with Daniel.  Your code uses classes that you wrote, and
> classes you got from somewhere else -- Sioux Unusuals, perhaps.
> And if those classes use ThreadLocals for their own purposes, and
> you blithely destroy them all, what happens then?  Or what about
> the class that invoked your code, passing an InheritableThreadLocal?
> Is it a good idea to change parts of your invoker's state that you
> don't understand, that you aren't even aware of?

Consider the use case again.  I've written a container.  It procures a 
thread and lets third-party code run in it.  Currently I have two choices:

1. Create a fresh thread each time.  This kills all the ThreadLocals that 
might be lying around, but doesn't perform very well.
2. Use a ThreadPool.  This improves performance at the cost of letting 
ThreadLocals packrat (which, in the worst case, holds entire ClassLoaders in 
memory).

I'm greedy; I want the performance without the memory issues.  Or, to say it 
another way, when getting a Thread from a ThreadPool, it should be 
completely indistinguishable whether it's a recycled or brand-new thread. 

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Thread

Proposed new Java feature "Mike Schilling" <mscottschilling@hotmail.com> - 2012-05-26 16:11 -0700
  Re: Proposed new Java feature Robert Klemme <shortcutter@googlemail.com> - 2012-05-27 13:32 +0200
    Re: Proposed new Java feature "Mike Schilling" <mscottschilling@hotmail.com> - 2012-05-27 11:14 -0700
      Re: Proposed new Java feature Robert Klemme <shortcutter@googlemail.com> - 2012-05-28 12:13 +0200
      Re: Proposed new Java feature v_borchert@despammed.com (Volker Borchert) - 2012-06-04 20:16 +0000
  Re: Proposed new Java feature markspace <-@.> - 2012-05-27 09:28 -0700
    Re: Proposed new Java feature "Mike Schilling" <mscottschilling@hotmail.com> - 2012-05-27 11:00 -0700
      Re: Proposed new Java feature Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-05-27 11:46 -0700
        Re: Proposed new Java feature "Mike Schilling" <mscottschilling@hotmail.com> - 2012-05-27 12:04 -0700
          Re: Proposed new Java feature Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-05-27 15:30 -0400
            Re: Proposed new Java feature "Mike Schilling" <mscottschilling@hotmail.com> - 2012-05-27 12:59 -0700
              Re: Proposed new Java feature Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-05-27 17:51 -0400
                Re: Proposed new Java feature markspace <-@.> - 2012-05-27 15:20 -0700
                Re: Proposed new Java feature Robert Klemme <shortcutter@googlemail.com> - 2012-05-28 12:13 +0200
                Re: Proposed new Java feature markspace <-@.> - 2012-05-28 08:28 -0700
                Re: Proposed new Java feature Robert Klemme <shortcutter@googlemail.com> - 2012-05-28 19:29 +0200
                Re: Proposed new Java feature markspace <-@.> - 2012-05-28 12:16 -0700
                Re: Proposed new Java feature Robert Klemme <shortcutter@googlemail.com> - 2012-05-28 22:58 +0200
                Re: Proposed new Java feature "Mike Schilling" <mscottschilling@hotmail.com> - 2012-05-28 21:40 -0700
                Re: Proposed new Java feature Robert Klemme <shortcutter@googlemail.com> - 2012-05-29 22:52 +0200
                Re: Proposed new Java feature "Mike Schilling" <mscottschilling@hotmail.com> - 2012-05-29 18:53 -0700
                Re: Proposed new Java feature Tom Anderson <twic@urchin.earth.li> - 2012-05-27 23:27 +0100
                Re: Proposed new Java feature Robert Klemme <shortcutter@googlemail.com> - 2012-05-28 12:22 +0200
                Re: Proposed new Java feature "Mike Schilling" <mscottschilling@hotmail.com> - 2012-05-27 21:43 -0700
                Re: Proposed new Java feature Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-05-29 14:32 +0000
  Re: Proposed new Java feature Tom Anderson <twic@urchin.earth.li> - 2012-05-27 18:43 +0100
  Re: Proposed new Java feature Kevin McMurtrie <mcmurtrie@pixelmemory.us> - 2012-06-02 12:41 -0700
    Re: Proposed new Java feature markspace <-@.> - 2012-06-02 15:55 -0700

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