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Re: Proposed new Java feature

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On Sun, 27 May 2012, Eric Sosman wrote:

> On 5/27/2012 3:59 PM, Mike Schilling wrote:
>> "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.
>>>>>>> 
>>>>>>> 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 understood it fine the first time around, thanks.

It seems to me that you did not.

> If you think of anything new to add, pray do so.

Mike added this pithy statement of the goal:

  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.

At the moment, it is *not* possible to achieve that, because ThreadLocals 
will survive recycling.

One way of looking at a thread pool is that it provides a supply of fresh 
short-lived virtual threads, implemented on top of long-lived real 
threads. Every time we take a thread out of the pool, we want it to appear 
brand-new. Deleting all ThreadLocals when a real thread is recycled is not 
"extremely dangerous", because at that moment, the *virtual* thread is 
dying, and a new one is being created; that makes it an entirely 
appropriate thing to do.

It is certainly true that it is "only a crutch for not doing the right 
thing to begin with", but the sad fact is that programmers persist in not 
doing the right thing to begin with, and it is useful for framework 
writers to be able to limit the damage they can cause.

tom

-- 
Mathematics is the door and the key to the sciences. -- Roger Bacon

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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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