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From Sylvain Wallez <sylv...@apache.org>
Subject Re: Weird multithreading bug in Cron block
Date Thu, 09 Jun 2005 21:41:18 GMT
Vadim Gritsenko wrote:

> Sylvain Wallez wrote:
>
>> Vadim Gritsenko wrote:
>>
>>> Anyways, RunnableManager's pools MUST NOT inherit any variables, 
>>> IMHO. I think you meant the same.
>>
>>
>>
>> Exactly. And my modifications ensure this CAN NOT happen, by simply 
>> suppressing the automatic inheritance of environment stack between 
>> child threads and their parent.
>
>
> Ok, Good. But now there is an incompatibility - hope you mention it at 
> least in status file.


Yep, I will. In the meantime, I've seen that DefaultIncludeCacheManager 
in 2.2 uses RunnableManager instead of "new Thread()", which is buggy as 
the thread used to load the URI won't inherit the environment of the 
request processing thread.

So I decided to refactor the CocoonThread I just added in a 
CocoonRunnable, which wraps a Runnable and sets up the environment stack 
before calling the wrapped object's run() method. That allows to use 
both "new Thread()" and thread pools.

>> For places where we *need* inheritance to happen such as in parallel 
>> include transformer, we now MUST use CocoonThread that does the 
>> environment stack copy, thus preserving the information needed to 
>> correctly resolve URIs in background threads. And in that case, we 
>> cannot use RunnableManager since its threads don't (and shouldn't) 
>> inherit the environement stack.
>
>
> IncludeTransformer does not rely on inheritable thread locals, as it 
> is now. It used to, though.


Note that with the InheritableThreadLocal, thread had no choice but 
inherit the environment stack of the parent thread. And using runnable 
manager means using a inherited context which isn't the right one. The 
CocoonRunnable should fix this.

>>> What's missing? :-?
>>
>>
>> The asynchronous nature of threads combined with the create-on-demand 
>> behaviour of pools.
>
>
> Gotcha.


Yeah, not easy :-)

Sylvain

-- 
Sylvain Wallez                        Anyware Technologies
http://apache.org/~sylvain            http://anyware-tech.com
Apache Software Foundation Member     Research & Technology Director


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