Where does the GC tracks the vmholder? I did a grep of 'vmholder' in all
the source code and I can't find anything.
There's a notion of injected fields in HotSpot which aren't present in
class declaration, but present in the class at runtime (for details see
JavaClasses::get_injected() called from ClassFileParser::parse_fields()).
vmholder is an object field injected into ResolvedMethodName class. It's
an ordinary object field, so there's no additional GC support needed to
support it.
Best regards,
Vladimir Ivanov
Thanks
- Ioi
On 5/7/18 5:45 PM, Vladimir Ivanov wrote:
Ioi,
Though the field is never accessed directly,
ResolvedMethodName::vmholder is still tracked by GC and keeps the
metadata it accompanies (RMN::vmtarget) alive until RMN is reachable.
Best regards,
Vladimir Ivanov
On 5/7/18 17:29, Ioi Lam wrote:
I don't see anywhere in HotSpot that uses
java_lang_invoke_ResolvedMethodName::_vmholder_offset, which is
declared here:
http://hg.openjdk.java.net/jdk/jdk/file/7444101401b2/src/hotspot/share/classfile/javaClasses.hpp#l1057
http://hg.openjdk.java.net/jdk/jdk/file/9608f7f41c4e/src/java.base/share/classes/java/lang/invoke/MemberName.java#l75
I tried commenting out the initialization of this field and was able
to run a simple Lambda test.
diff -r 9255cb73f048 src/hotspot/share/classfile/javaClasses.cpp
--- a/src/hotspot/share/classfile/javaClasses.cpp Mon May 07
15:29:31 2018 -0700
+++ b/src/hotspot/share/classfile/javaClasses.cpp Mon May 07
17:27:27 2018 -0700
@@ -3808,7 +3808,7 @@
// Add a reference to the loader (actually mirror because
anonymous classes will not have
// distinct loaders) to ensure the metadata is kept alive.
// This mirror may be different than the one in clazz field.
- new_resolved_method->obj_field_put(_vmholder_offset,
m->method_holder()->java_mirror());
+ //new_resolved_method->obj_field_put(_vmholder_offset,
m->method_holder()->java_mirror());
resolved_method =
ResolvedMethodTable::add_method(Handle(THREAD, new_resolved_method));
}
Any plans to use vmholder in the future? Or, is this used by any
non-HotSpot VM?
If no one uses it, I'll file an RFE to remove it, so we can save a
pointer per MemberName.
Thanks
- Ioi
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