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From Patricia Shanahan <p...@acm.org>
Subject Re: ThreadPool calling Thread.setName
Date Sat, 27 Apr 2013 12:55:38 GMT
I'll read the paper. However, C and C++ tend to have nastier semantics 
for data races than Java, which lacks anything quite as drastic as the C 
definition of "undefined behavior".

My reasoning for the relative safety of this particular race is based on 
one of the more basic rules, atomicity of reference read or write, 
combined with reading the relevant code. Regardless of data races, the 
result of accessing "name" will always be a pointer to a char[]. We have 
a significant chance of the char[] containing useful, helpful data in 
the old version of the code. The probability of it containing anything 
useful is zero in the new version.


On 4/27/2013 3:51 AM, Peter Firmstone wrote:
> Ok found the link, the paper's called:
> Position paper: Nondeterminism is unavoidable, but data races are
> pure evil
> http://www.hpl.hp.com/techreports/2012/HPL-2012-218.pdf
> Wheather Thread's name field is an issue or not depends on the code that
> uses it (Object.toString() and Thread.getName() methods do) and what
> that code does with the information.
> Outrigger uses it in lifecycle logs, although it doesn't appear to be
> called on any threads from ThreadPool.  Instead Outrigger calls
> getName() on threads it references from fields in OutriggerServerImpl.
> These fields have since been changed to final, so if the name is set
> during construction and not changed after publication, it's thread safe,
> in addition these threads aren't started until after
> OutriggerServerImpl's constructor returns.
> The concurrency issues I most recently experienced were related to
> Outrigger, I couldn't determine the cause of these failures, perhaps I
> lack sufficient ability to reason deeply about these issues, my fix for
> the problem was akin to carpet bombing; fix every concurrency problem
> and that appears to have paid off.
> It's very difficult to determine if toString() may be called on
> ThreadPool threads.  I reasoned it could be and that was sufficient
> justification to not use setName().
> Cheers,
> Peter.
> On 27/04/2013 1:20 AM, Patricia Shanahan wrote:
>> I've looked at the source code. The field "name" that is shared
>> between threads doing getName or setName on a given Thread is a
>> reference. Writes and reads of references are always atomic.
>> The worst that could happen is that the change to the name does not
>> propagate to all threads that might display information about the
>> thread. The proposed fix ensures that worst case outcome happens all
>> the time.
>> Patricia
>> On 4/26/2013 5:44 AM, Greg Trasuk wrote:
>>> I'm curious, as I don't see any indication in the Javadocs that
>>> setName() isn't thread safe.  Is there another reference that calls that
>>> out?  And what would be the failure mode, apart from a mangled string in
>>> a log output?
>>> Personally, if the potential failure mode wasn't onerous, I'd opt for
>>> more descriptive logging.  Comprehensibility is everything when you're
>>> troubleshooting.
>>> Cheers,
>>> Greg.
>>> On Fri, 2013-04-26 at 05:48, Peter Firmstone wrote:
>>>> Hope you don't mind, I've removed the call to Thread.setName in
>>>> com.sun.jini.ThreadPool
>>>> As a result threads will be less descriptive, unfortunately setName
>>>> isn't thread safe, it's final and cannot be overridden.  Thread.getName
>>>> is only thread safe if a Thread's name isn't changed after publication.
>>>> ThreadPool was the only instance of Thread.setName in River.
>>>> Regards,
>>>> Peter.

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