RFR(S) 8240244 Avoid calling resolve_super_or_fail in SystemDictionary::load_shared_class

[Ioi Lam]

On 3/3/20 3:15 AM, Claes Redestad wrote:
> Hi Ioi,
>
> overall looks good, thanks!
>
> systemDictionary.cpp
>
> I'm not sure what you meant to write here:
>
> +  // + Don't take the lock if loader data is NULL without taking lock.

Sorry I was sloppy when editing :-(. I meant:

// + Don't take the lock if loader data is NULL.

>
>
> Left-over "!= 0":
>
> +  if (!super_type->is_shared_unregistered_class() != 0 && 
> super_type->class_loader_data() != NULL) {
>

Fixed.

Thanks
- Ioi
> -- 
>
> It seems to me that it might be possible to take the
> SystemDictionary_lock just once in check_shared_class_super_types
> method, spanning super and all interfaces. That might need some
> restructuring since we can't hold that lock when going into
> the class-loading slow path, but I think the slow path could profitably
> be moved to the outer method outside such a locked section.
>
> Thanks!
>
> /Claes
>
> On 2020-03-03 07:34, Ioi Lam wrote:
>> https://bugs.openjdk.java.net/browse/JDK-8240244
>> http://cr.openjdk.java.net/~iklam/jdk15/8240244-reduce-resolve-super.v01/ 
>>
>>
>> When loading shared classes from the CDS archive, we need to test if the
>> actually loaded super types are the same as those used during CDS 
>> dumping.
>> That was done with a pretty expensive call to resolve_super_or_fail.
>>
>> In most cases, the super type has already been loaded (about 350 out 
>> of 400
>> cases when running HelloWorld), so we can quickly determine that by
>> doing a look up in the super type's dictionary.
>>
>> This saves about 250,000 out of about 112M instructions (about 0.22%) 
>> when
>> running HelloWorld with the default archive on Linux/x64.
>>
>> I also renamed a few functions in instanceKlass.hpp to 
>> _xxx_shared_xxx since
>> they are used only for CDS.
>>
>> Thanks
>> - Ioi
>>
>>