ant-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Matt Benson <gudnabr...@yahoo.com>
Subject Re: race conditions in Ant
Date Thu, 04 Oct 2007 19:20:58 GMT

--- Steve Loughran <stevel@apache.org> wrote:

> Steve Loughran wrote:
> > 
> > 
> > I've been running the new build and havent seen
> any more loops; I think 
> > race conditions are gone.
> > 
> > Incidentally, given we didnt see any way that the
> thing could loop, 
> > given we were using threadlocal to store a
> per-thread datastructure, and 
> > given that threadlocals are implicitly thread
> safe, I'm still not sure 
> > where the problem arose. but I have been pointed
> at some bugs in 
> > ThreadLocal
> > 
> > 
> >
>
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6550283
> > "ThreadLocal.initialValue() may be called multiple
> times in some cases"
> > 
> > There is a bit of a race condition on
> initialisation, *across all 
> > threadlocal classes in use in that thread*. if you
> are only using your 
> > own classes, you need to sync off something common
> (like the current 
> > thread). But you are still vulnerable to any other
> class using Thread 
> > local storage making an operation that increases
> the size of the hash 
> > table of threadlocal values, in which case you are
> stuffed.
> > 
> > This is a WONTFIX for Java<1.6.
> > 
> > Accordingly, you can't reliably use ThreadLocal on
> a multicpu system for 
> > Java <=1.5 as you cannot be sure that other
> classes wont stamp on you. 
> > This is pretty serious, as the reason you would
> use TLS is to avoid 
> > concurrency problems.
> 
> followup based on looking at the code.

Which code, Steve?

Thanks,
Matt

> 
> Its not a race condition, so much as a re-entrancy
> bug. the code here is 
> thread safe, but doesnt lock out the per-thread
> hashmap  while 
> initialising a ThreadLocal instance. If the thing
> being initialised is 
> subclassed to make a complex initial value, and that
> initial value 
> itself creates ThreadLocal content, then you are in
> trouble. If you dont 
> do that, you should be ok.
> 
> This is probably not the cause of the looping I saw.
> 
> -steve
> 
> 
>
---------------------------------------------------------------------
> To unsubscribe, e-mail:
> dev-unsubscribe@ant.apache.org
> For additional commands, e-mail:
> dev-help@ant.apache.org
> 
> 



       
____________________________________________________________________________________
Pinpoint customers who are looking for what you sell. 
http://searchmarketing.yahoo.com/

---------------------------------------------------------------------
To unsubscribe, e-mail: dev-unsubscribe@ant.apache.org
For additional commands, e-mail: dev-help@ant.apache.org


Mime
View raw message