8230116: Test workaround to Klass::_class_loader_data sometimes NULL problem

This is a low frequency problem that we are seeing internally, this patch is mostly to rule out one theory.

Reviewed-by: dcubed

src/hotspot/share/oops/klass.cpp

@@ -568,6 +568,12 @@ void Klass::restore_unshareable_info(ClassLoaderData* loader_data, Handle protec
     // Restore class_loader_data to the null class loader data
     set_class_loader_data(loader_data);
 
+    // Workaround for suspected bug.  Make sure other threads see this assignment.
+    // This shouldn't be necessary but the compiler thread seems to be behind
+    // the times, even though this thread takes MethodCompileQueue_lock and the thread
+    // that doesn't see this value also takes that lock.
+    OrderAccess::fence();
+
     // Add to null class loader list first before creating the mirror
     // (same order as class file parsing)
     loader_data->add_class(this);