RFR 8080225 FileInput/OutputStream/FileChannel cleanup should be improved

[Roger Riggs]

Hi Peter,

Thanks for reviewing.

This is a transition step to removing the finalize method completely 
while giving subclasses
notice to upgrade their cleanup activities and yet gain the performance 
benefits sooner.
Later, finalize() and related compatibility mechanisms will be removed.
Simpler code, even if sometimes less than optimal is preferred to 
maintain compatibility in the interim.

...

On 12/4/2017 9:25 AM, Peter Levart wrote:
> Hi Roger,
>
> On 12/04/2017 03:09 PM, Peter Levart wrote:
>>
>>
>> On 12/04/2017 02:25 PM, Peter Levart wrote:
>>> Hi Rogger,
>>>
>>> On 12/04/2017 02:17 PM, Peter Levart wrote:
>>>> Hi Rogger,
>>>>
>>>> Interesting approach. Conditional finalization. You use 
>>>> finalization to support cases where user overrides finalize() 
>>>> and/or close() and Cleaner when he doesn't.
>>>>
>>>> I wonder if it is the right thing to use AltFinalizer when user 
>>>> overrides finalize() method. In that case the method is probably 
>>>> not empty and calls super.finalize() (if it is empty or doesn't 
>>>> call super, user probably doesn't want the finalization to close 
>>>> the stream) and so normal finalization applies. If you register 
>>>> AltFinalizer for such case, close() will be called twice.
>>>
>>> Ah, scrap that. I forgot that XXXStream.finalize() is now empty, so 
>>> user overriding it and calling super does not in fact close the 
>>> stream. You have to register AltFinalizer in that case. But now I 
>>> wonder if the logic should still be 3-state and do the following:
>>>
>>> - if user overrides finalize() - use AltFinalizer to call both: 
>>> first finalize() and then close(); else
>>> - if user overrides close() - use AltFinalizer to call close(); else
>>> - use Cleaner
>>>
>>> What do you think?
>>>
>>> Regards, Peter
>>>
>>
>> I just realized that in the above case when finalize is overridden, 
>> it would be called twice. once by finalization and once by 
>> AltFinalizer. So your logic is as correct as it can be for that case 
>> (to just call close() with AltFinalizer). The only problem is order 
>> which is arbitrary, so it may happen that AltFinalizer calls close() 
>> 1st and then finalization calls overridden finalize() method which 
>> might expect the stream to still be open until it calls 
>> super.finalize().
>>
>> Regards, Peter
>>
>
> Final refinement... (hopefully!)
>
> If user overrides just finalize() and does not override close(), then 
> it might be best to employ Cleaner to close the stream. Cleaner is 
> Phantom based and will get fired after finalization invokes overridden 
> finalize(), enabling the finalize() method to still access the stream 
> in that case. So this is the final logic (I think):
>
> - if user overrides close(), use AltFinalizer to call close(); else
> - use Cleaner to close the stream
>
> The above logic in action:
>
> finalize()              close()                        action
>
> not overridden    not overridden           Cleaner closes stream
> not overridden    overridden                 AltFinalizer calls close()
> overridden          not overridden           finalization calls 
> finalize() then Cleaner closes stream
> overridden          overridden                 finalization calls 
> finalize() and AltFinalizer calls close() (in arbitrary order)

Right, if close() is not overridden the behavior of close() is known and 
the Cleaner can be used.

The contents of an overridden finalize() method are unknowable, it may 
or may not call close() itself
and may or may not call super.finalize().  If  close() is called, then 
the Cleaner will be removed; otherwise it will release the resources.
The close method should be idempotent, calling it twice should not be a 
problem.

This does simplify the logic.

Thanks, Roger


>
>
> Regards, Peter
>