I'm thinking of adding a final method to Object: final void useSameLockAs(Object another);
What it does is to make "this" give up on its own lock object and use the same lock as "another". Probably this may restrict implementations to some degree (e.g. I'm not sure how that would work with thin locks).
The advantage is that you can easily create lists, trees etc. that ostensibly use one lock per object, when they really all use only one lock, as the doctor prescribed.
The catch is that this only works well if the cost of recursive acquire (acquiring an already-acquired lock) is low enough. I haven't kept up with the relative costs; last time I looked recursive locks were still quite expensive, but I think the tradeoffs have changed a fair amount. Does anyone have some hard data?
Andrei
