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

[David Holmes]

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> 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
>>>>
>>>
>>>
>>