Robin, Thanks for helping clarify the issues. The MMTk code base we are using is what Steve Blackburn supplied us in mid July. I don't know when it will be suggested we move to a more recent version of MMTk. I suspect a major part of the confusion has been because of working with a code base where the Plan interface is in transition.
In any case, please confirm that each java thread needs to put an instance of Plan in its thread-local storage and that writeBarrier() and alloc() virtual method entry points need to be materialized from thread-local Plan object. Also, please confirm (or deny) that we should never call VM.barriers.performWriteInBarrier(). It only should be called by internal MMTk methods (I think). On 10/11/06, Robin Garner <[EMAIL PROTECTED]> wrote:
I think you must be looking at a fairly old version of MMTk. writeBarrier is an instance method of a MutatorContext (in org.mmtk.plan). MutatorContext exists to hold unsynchronized thread-local data structures. Particularly relevant to the write barrier, each mutator context has its own thread-local remset. All of the mutator context methods of MMTk need fast access to the MMTk thread local data structures, which is why they are instance methods. The other critical instance method of a MutatorContext is 'alloc', which also has it's thread-local chunk of the space(s) it allocates into. As far as the VM is concerned, it will be calling instance methods of a final class. The various classes in org.mmtk.plan.* aren't final, but the VM interface code is expected to wrap the currently selected plan in some final class. JikesRVM wraps the currently selected plan classes in a 'SelectedPlan', 'SelectedMutatorContext' etc. As far as the VM.barriers.performWriteInBarrier() call is concerned, the optimization required to devirtualize a call to a final method of a static final field shouldn't be too hard to implement. MMTk recently moved away from using static methods for this part of the interface, to the current abstract factory, and improved the structure of the software significantly. We don't want to go back! > I erroneously thought we could call > VM.barriers.performWriteInBarrier() directly. This sort of, kind of breaks > MMTk architecture. well, it less 'breaks the architecture' than performs a no-op :) -- robin Weldon Washburn wrote: > Ooops. I really tangled things up. You are right about how we are > supposed > to find the Java write barrier method. It is located in > Plan.writeBarrier(). > Each GC algorithm has a Plan class that overrides the writeBarrier() > method. I erroneously thought we could call > VM.barriers.performWriteInBarrier() directly. This sort of, kind of breaks > MMTk architecture. By design, each GC algorithm in MMTk is supposed to > call > Plan.writeBarrier() which, in turn, will call > VM.barriers.performWriteInBarrier. > > Sorry for the confusion. > > > > > On 10/10/06, Mikhail Fursov <[EMAIL PROTECTED]> wrote: >> >> Yes, we can run the usual inliner after helpers are inlined. >> The only problem I want to notice is that once we have different helpers >> for >> different GCs it's a bad idea to use virtual method calls in performance >> sensitive helpers. You are allowed to do it, but the better solution >> is to >> teach the helper to use a final implementation of the Barrier and replace >> the helper once the implementation of the Barrier class is changed. >> >> On 10/11/06, Rana Dasgupta <[EMAIL PROTECTED]> wrote: >> > >> > Makes sense, using a standard barrier invocation fastpath. But I assume >> > that >> > the MMTk WB helper that it will call needs to be inlined too. >> > >> > Thanks >> > >> > >> > On 10/10/06, Mikhail Fursov <[EMAIL PROTECTED]> wrote: >> > > >> > > Weldon, >> > > > I thought about slightly different approach. >> > > > Why not to write fast-path VM helper like was proposed in the >> thread >> > > > "[drlvm]Extending..." >> > > > This helper (a static method) can be inlined by JIT without any >> > > > devirtualization and call any method needed from MMTk or native >> > > > implementation. So JIT won't know if it works with MMTk or with a >> > native >> > > > GC: >> > > > all you need is just to replace the Java version of the helper. >> > > > ? >> > > > >> > > >> > > >> > >> > >> >> >> -- >> Mikhail Fursov >> >> > > --------------------------------------------------------------------- Terms of use : http://incubator.apache.org/harmony/mailing.html To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
-- Weldon Washburn Intel Middleware Products Division
