--- Steve Loughran <[EMAIL PROTECTED]> 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
>
>
>
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