Restrictions for lock coarsening?

[Christian Thalinger]

On Tue, 2009-01-06 at 10:30 -0800, Tom Rodriguez wrote:
> >> This means that objects created during that time period
> >> aren't allowed to use biased locking.
> >
> > Throughout the whole lifetime?
> 
> Throughout the whole lifetime of that object.  Biased locking  
> maintains state in the header of an object which says whether it can  
> be biased or not.  The initial state is read from its the class  
> object's Klass::_prototype_header field at allocation time and is  
> written into the header word.  The biased locking startup delay works  
> by having every classes initial state be not biasable and then after  
> the delay expires they are all marked as biasable.  Every object  
> allocated after that point will be biasable.  It's definitely an  
> unsatisfying solution.

It's already some time ago I looked at the biased-locking code... is it
possible at all to revoke contented locks (or CAS-based locks) to be
biasable?  If yes, is the "not-biasable" state different to CAS-based
locks?

- Christian