RFR 6642881: Improve performance of Class.getClassLoader()

Frederic Parain frederic.parain at oracle.com
Tue Jun 24 08:41:40 UTC 2014

Hi Coleen,

It seems that there's still a reference to JVM_GetClassLoader
in file jdk/src/share/native/common/check_code.c. The code looks
like dead code, but it would be nice to clean it up.



On 06/24/2014 01:45 AM, Coleen Phillimore wrote:
> Please review a change to the JDK code for adding classLoader field to
> the instances of java/lang/Class.  This change restricts reflection from
> changing access to the classLoader field.  In the spec,
> AccessibleObject.setAccessible() may throw SecurityException if the
> accessibility of an object may not be changed:
> http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/AccessibleObject.html#setAccessible(boolean)
> Only AccessibleObject.java has changes from the previous version of this
> change.
> open webrev at http://cr.openjdk.java.net/~coleenp/6642881_jdk_4/
> bug link https://bugs.openjdk.java.net/browse/JDK-6642881
> Thanks,
> Coleen
> On 6/19/14, 11:01 PM, David Holmes wrote:
>> On 20/06/2014 6:53 AM, Joel Borggrén-Franck wrote:
>>> Hi Mandy,
>>> On 19 jun 2014, at 22:34, Mandy Chung <mandy.chung at oracle.com> wrote:
>>>> On 6/19/14 12:34 PM, Joel Borggrén-Franck wrote:
>>>>> Hi,
>>>>> On 19 jun 2014, at 20:46, Coleen Phillimore
>>>>> <coleen.phillimore at oracle.com> wrote:
>>>>>> On 6/17/14, 12:38 AM, Joel Borggrén-Franck wrote:
>>>>>>> Have you considered hiding the Class.classLoader field from
>>>>>>> reflection? I’m not sure it is necessary but I’m not to keen on
>>>>>>> the idea of people poking at this field with Unsafe (which should
>>>>>>> go away in 9 but …).
>>>>>> I don't know how to hide the field from reflection.  It's a
>>>>>> private final field so you need to get priviledges to make it
>>>>>> setAccessible.  If you mean injecting it on the JVM side, the
>>>>>> reason for this change is so that the JIT compilers can inline
>>>>>> this call and not have to call into the JVM to get the class loader.
>>>>> There is sun.reflect.Reflection.registerFieldsToFilter() that hides
>>>>> a field from being found using reflection. It might very well be
>>>>> the case that private and final is enough, I haven’t thought this
>>>>> through 100%. On the other hand, is there a reason to give users
>>>>> access through the field instead of having to use
>>>>> Class.getClassLoader()?
>>>> There are many getter methods that returns a private final field.
>>>> I'm not sure if hiding the field is necessary nor a good precedence
>>>> to set. Accessing a private field requires "accessDeclaredMember"
>>>> permission although it's a different security check (vs
>>>> "getClassLoader"
>>>> permission).  Arguably before this new classLoader field, one could
>>>> call Class.getClassLoader0() via reflection to get a hold of class
>>>> loader.
>>>> Perhaps you are concerned that the "accessDeclaredMember" permission
>>>> is too coarse-grained?  I think the security team is looking into
>>>> the improvement in that regards.
>>> I think I’m a bit worried about two things, first as you wrote,
>>> “accessDeclaredMember” isn’t the same as “getClassLoader”, but since
>>> you could get the class loader through getClassLoader0() that
>>> shouldn’t be a new issue.
>>> The second thing is that IIRC there are ways to set a final field
>>> after initialization. I’m not sure we need to care about that either
>>> if you need Unsafe to do it.
>> Normal reflection can set a final field if you can successfully call
>> setAccessible(true) on the Field object.
>> David
>> -----
>>> cheers
>>> /Joel

Frederic Parain - Oracle
Grenoble Engineering Center - France
Phone: +33 4 76 18 81 17
Email: Frederic.Parain at oracle.com

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