Restrictions for lock coarsening?

[David Holmes - Sun Microsystems]

Christian Thalinger said the following on 01/09/09 09:33:
> On Fri, 2009-01-09 at 08:27 +1000, David Holmes - Sun Microsystems
> wrote:
>> Also note, as I understand from work I did late in the Java 6 cycle, 
>> once an object has its biased revoked it remains revoked ie it will not 
>> participate in biased-locking again. This was done to prevent 
>> "thrashing" and it also makes things easier to reason about.
> 
> Looking at bulk_revoke_or_rebias_at_safepoint(), it seems you're right.
> Even worse.  All future instances of a class cannot use biased locking,
> as this comment states:
> 
>     // Disable biased locking for this data type. Not only will this
>     // cause future instances to not be biased, but existing biased
>     // instances will notice that this implicitly caused their biases
>     // to be revoked.
> 
> Or am I wrong?

I read that comment the same way, but I never did get a full grip on the 
biased locking lifecycle. Perhaps a re-read of the technical 
descriptions will shed more light - see the linke to the Detlefs & 
Russell paper in Dave Dice's blog:

http://blogs.sun.com/dave/entry/biased_locking_in_hotspot

David Holmes