RFR 6642881: Improve performance of Class.getClassLoader() (original) (raw)

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.

Thanks,

Fred

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/6642881jdk4/ > 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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