Andrew Haley writes:
> Andrew John Hughes writes:
> > Hi everyone,
> >
> > I've recently been trying to build JikesRVM on a Free platform (using CACAO
> > and some hacked up tools from OpenJDK in the form of IcePick). I've got it
> > just about there now, but I've been let down by a missing native method.
> >
> > Within the java.util.concurrent framework, the class AtomicLong has a native
> > method, VMSupportsCS8 which CACAO at least doesn't provide. It's basically
> > just a check method to find out whether the VM supports lockless compare-set
> > operations on longs.
> >
> > >From java.util.concurrent.atomic.AtomicLong:
> >
> > /**
> > * Records whether the underlying JVM supports lockless
> > * CompareAndSet for longs. While the unsafe.CompareAndSetLong
> > * method works in either case, some constructions should be
> > * handled at Java level to avoid locking user-visible locks.
> > */
> > static final boolean VM_SUPPORTS_LONG_CAS = VMSupportsCS8();
> >
> > /**
> > * Returns whether underlying JVM supports lockless CompareAndSet
> > * for longs. Called only once and cached in VM_SUPPORTS_LONG_CAS.
> > */
> > private static native boolean VMSupportsCS8();
> >
> > Has anyone implemented this so far? So near, but yet so far!
>
> Yes, it's in libgcj, of course.
>
> jboolean
> java::util::concurrent::atomic::AtomicLong::VMSupportsCS8 ()
> {
> // FIXME
> return false;
> }
Actually, I didn't quite tell you the *whole* truth: VMSupportsCS8 is
also a gcj builtin. The code in libgcj is a fallback that gets called
only if libgcj is built with no optimization.
Andrew.
