[8u40] RFR 6642881: Improve performance of Class.getClassLoader()

[David Holmes]

On 29/07/2016 5:55 PM, Leela Mohan wrote:
> Hi David,
>
> I understand, Klass types are no longer oops
>  but JNIHandles::resolve_non_null() would expose naked oops. In other
> words, KlassOops are no longer oops but java.lang.Class objects are.

Yes my mistake - focusing on the wrong aspect. Good catch.

Thanks,
David

> Thanks,
> Leela
>
> On Thu, Jul 28, 2016 at 10:51 PM, David Holmes <david.holmes at oracle.com
> <mailto:david.holmes at oracle.com>> wrote:
>
>     Hi Leela,
>
>     On 29/07/2016 12:59 PM, Leela Mohan wrote:
>
>         I think, change in the file unsafe.cpp is incorrect. (
>         http://cr.openjdk.java.net/~coleenp/6642881_8u40_hotspot/ )
>
>         Below function is accessing naked oops when thread has
>         transitioned to
>         "native":
>
>         *+ static jobject get_class_loader(JNIEnv* env, jclass cls)
>         {**+   if
>         (java_lang_Class::is_primitive(JNIHandles::resolve_non_null(cls)))
>         {**+     return NULL;**+   }**+   Klass* k =
>         java_lang_Class::as_Klass(JNIHandles::resolve_non_null(cls));**+   oop
>         loader = k->class_loader();**+   return JNIHandles::make_local(env,
>         loader);**+ }*
>
>
>     klass types are no longer oops in the Java heap, but metaspace
>     objects that reside in a per-classloader allocation region. They
>     never get compacted or relocated so raw pointers to them are safe.
>
>     Cheers,
>     David
>
>
>
>         - Leela
>
>         On Mon, Sep 8, 2014 at 7:05 PM, Coleen Phillimore <
>         coleen.phillimore at oracle.com
>         <mailto:coleen.phillimore at oracle.com>> wrote:
>
>
>             Thanks, Mandy!
>
>             Coleen
>
>
>             On 9/8/14, 6:59 PM, Mandy Chung wrote:
>
>                 Thumbs up.
>
>                 Mandy
>
>                 On 9/5/2014 12:55 PM, Coleen Phillimore wrote:
>
>                     Summary: Add classLoader to java/lang/Class instance
>                     for fast access
>
>                     This is a backport request for 8u40.   This change
>                     has been in the jdk9
>                     code for 3 months without any problems.
>
>                     The JDK changes hg imported cleanly.  The Hotspot
>                     change needed a hand
>                     merge for create_mirror call in klass.cpp.
>
>                     http://cr.openjdk.java.net/~coleenp/6642881_8u40_jdk/
>                     http://cr.openjdk.java.net/~coleenp/6642881_8u40_hotspot/
>
>                     bug link
>                     https://bugs.openjdk.java.net/browse/JDK-6642881
>
>                     Ran jdk_core jtreg tests in jdk with both
>                     jdk/hotspot changes. Also ran
>                     jck java_lang tests with only the hotspot change.
>                     The hotspot change can
>                     be tested separately from the jdk change (but not
>                     the other way around).
>
>                     Thanks,
>                     Coleen
>
>
>
>
>