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From Peter Firmstone <j...@zeus.net.au>
Subject Re: com.sun.jini.thread lock contention
Date Sun, 04 Jul 2010 22:16:07 GMT
About the same time I patched the source, TaskThread should now 
implement Runnable and encapsulates Thread rather than extending it, to 
avoid the race, the Thread is created inside the TaskTread constructor - 
from memory.

I'm pretty sure the patch made it into SVN?

Peter.

Patricia Shanahan wrote:
> Christopher Dolan wrote:
>> Attached is a minimalist initial patch.  I'm not happy that I had to
>> store a reference to the thread in the Runnable...  But otherwise I
>> wasn't sure how to interrupt it from removeTask() without a separate map
>> of TaskThread to Thread.  There's all a null pointer race in this patch
>> if you try to remove a task before it's run() method executes.
>
> I am concerned about the null pointer race, and think it may last a 
> little bit longer on some multiprocessor systems than is immediately 
> obvious.
>
> The first thing in the life of the new thread that I can see 
> establishing a "happens-before" relationship 
> [http://java.sun.com/docs/books/jls/third_edition/html/memory.html#17.4.5] 
> from the write to reads of myThread is the end of the first execution 
> of the synchronized block in the run method. In a multiprocessor with 
> release consistency, the write might not be visible to another thread 
> that wins the race for the TaskManager synchronization, even if it has 
> already happened on a processor running the new thread.
>
> The race could be removed by having a method:
>
> private void setThread(Thread t){
>   myThread = t;
> }
>
> in the Runnable, and having the thread creation code call it 
> immediately before starting the thread. At that point, the thread 
> creation code has references to both the Thread and the Runnable, and 
> is synchronized on the TaskManager object.
>
> Apologies for not writing, testing, and presenting a modified version 
> of the patch - I am having problems running qa on my WindowsXP system.
>
> Patricia
>
>
>


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