Request for review: 8004698: Implement Core Reflection for Type Annotations (original) (raw)

Joel Borggrén-Franck joel.franck at oracle.com
Tue Jan 22 12:47:45 UTC 2013

Hi Peter,

Thanks for your comments, see inline,

On 01/19/2013 06:11 PM, Peter Levart wrote:

I see, there is a dilema how to cache type annotations. To satisfy single-annotation-returning methods and repeating annotation logic, a HashMap would be a logical choice, but it has much bigger footprint than simple arrays of annotations...

I don't prioritize footprint for classes that have runtime visible type annotations. Those classes should be very few, and as a user you are making an explicit choice of adding metadata when you use runtime visible (type) annotations.

So here is my list of priorities (and by un-annotated I mean without runtime visible annotations):

I experimented with an idea of using a special purpose immutable Map implementation:

https://github.com/plevart/jdk8-tl/blob/anno-map/jdk/src/share/classes/sun/reflect/annotation/UniqueIndex.java and: https://github.com/plevart/jdk8-tl/blob/anno-map/jdk/src/share/classes/sun/reflect/annotation/AnnotationMap.java This is just a preview. I still have to create some tests to see how it compares to HashMap. Being an immutable wrapper for a single array of annotations it has a nice feature that a reference to it can be passed to other threads via a data race with no danger of data inconsistency, which simplifies caching mechanisms and helps scalability. Might even be a space-saving replacement for existing HashMaps of annotations. Depending on performance, of course. What do you think? Is it worth pursuing this further?

I'd be very hesitant to introduce a new hashmap like type. Especially since IMHO footprint when we actually have annotations isn't as critical as when we are annotation free.

My initial approach is probably to dust of your patches for an annotations cache on Class and adopt it for type annotations, and use on Field/Method/Constructor/(TypeVar).

Thank you again for your work on this!

cheers /Joel

Regards, Peter

On Jan 17, 2013 5:24 PM, "Joel Borggrén-Franck" <joel.franck at oracle.com_ _<mailto:joel.franck at oracle.com>> wrote: Hi, Here is a webrev for core reflection support for type annotations: http://cr.openjdk.java.net/~jfranck/8004698/webrev.00/ This code is based on the tl/jdk repository, but in order to run the tests you need a javac with type annotations support and also a recent copy of the VM that includes this change set: http://hg.openjdk.java.net/hsx/hotspot-main/hotspot/rev/35431a769282 (This also means this code can't be pushed until all supporting pieces are in place.) Type annotations are still a bit of a moving target so there will be follow up work on this. There is no caching of annotations in this version and I am not sure how we want to do the space/time trade of for type annotations. cheers /Joel

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