static {
// The Holder class will contain pre-generated DirectMethodHandles resolved
// speculatively using MemberName.getFactory().resolveOrNull. However, that
// doesn't initialize the class, which subtly breaks inlining etc. By forcing
// initialization of the Holder class we avoid these issues.
UNSAFE.ensureClassInitialized(Holder.class);
}
/*non-public*/ static boolean shouldBeInitialized(MemberName member) {
switch (member.getReferenceKind()) {
case REF_invokeStatic:
case REF_getStatic:
case REF_putStatic:
case REF_newInvokeSpecial:
break;
default:
// No need to initialize the class on this kind of member.
return false;
}
Class<?> cls = member.getDeclaringClass();
if (cls == ValueConversions.class || cls == MethodHandleImpl.class || cls == Invokers.class) {
// These guys have lots of <clinit> DMH creation but we know
// the MHs will not be used until the system is booted.
return false;
}
if (VerifyAccess.isSamePackage(MethodHandle.class, cls)
|| VerifyAccess.isSamePackage(ValueConversions.class, cls)) {
// It is a system class. It is probably in the process of
// being initialized, but we will help it along just to be safe.
if (UNSAFE.shouldBeInitialized(cls)) {
UNSAFE.ensureClassInitialized(cls);
}
return false;
}
return UNSAFE.shouldBeInitialized(cls);
}
@Override
protected WeakReference<Thread> computeValue(Class<?> type) {
UNSAFE.ensureClassInitialized(type);
if (UNSAFE.shouldBeInitialized(type))
// If the previous call didn't block, this can happen.
// We are executing inside <clinit>.
return new WeakReference<>(Thread.currentThread());
return null;
}
private static boolean checkInitialized(MemberName member) {
Class<?> defc = member.getDeclaringClass();
WeakReference<Thread> ref = EnsureInitialized.INSTANCE.get(defc);
if (ref == null) {
return true; // the final state
}
Thread clinitThread = ref.get();
// Somebody may still be running defc.<clinit>.
if (clinitThread == Thread.currentThread()) {
// If anybody is running defc.<clinit>, it is this thread.
if (UNSAFE.shouldBeInitialized(defc))
// Yes, we are running it; keep the barrier for now.
return false;
} else {
// We are in a random thread. Block.
UNSAFE.ensureClassInitialized(defc);
}
assert (!UNSAFE.shouldBeInitialized(defc));
// put it into the final state
EnsureInitialized.INSTANCE.remove(defc);
return true;
}