Hash locks and pointer-free allocation

Fri Dec 7 18:12:00 GMT 2001

I don't think that hash synchronization is neccessarily a prerequisite 
for having pointer free objects specially allocated.
Firstly, no Java object is ever _really_ pointer-free, because of the 
class descriptor (vtable) pointer. I suppose the GC assumes that pointer 
free classes themselves are never GC-allocated? Thats no problem for 
things like primitive arrays (and perhaps all native classes), but not 
marking the vtable will prevent Class GC for classes loaded from 
bytecode with a custom classloader.
Even without hash synchronization we can still have pointer free 
allocation provided the "fat" synchronization info data is allocated as 
uncollectable. We can free them using finalizer chaining on the monitor. 
I don't think this would be much of a performance hit because "fat" 
locks would only occur for contended monitors and they are very rare.
regards
Bryce.