Hi all,
Ok, no problem. So here's a patch that summarizes what I did in the
previous patch, but only for reflective fields (Field[], Method[],
Constructor[]) not including annotations:
http://dl.dropbox.com/u/101777488/jdk8-tl/JEP-149.c/webrev/index.html
The annotations part is unchanged semantically, but I had to:
- modify private method clearCachesOnClassRedefinition to only include
invalidation of annotations and declaredAnnotations fields. I also
renamed it to clearAnnotationCachesOnClassRedefinition
- renamed lastRedefinedCountto lastAnnotationsRedefinedCountand, since
this field is now only accessed while holding a lock (from synchronized
initAnnotationsIfNecessary), I removed the volatile keyword.
That's it.
While looking at this unchanged part of code some more, I see other
races as well. For example: two concurrent accesses to annotations
combined with redefinition of a class can result in NPE. Here's a serial
execution:
Thread 1:
getAnnotation(annotationType);
initAnnotationsIfNecessary();
VM:
classRedefinedCount++;
Thread 2:
getAnnotation(annotationType);
initAnnotationsIfNecessary();
clearAnnotationCachesOnClassRedefinition();
annotations = null;
Thread 1:
return AnnotationSupport.getOneAnnotation(annotations,
annotationClass);
// 'annotations' field can be null
So this needs to be fixed sooner or later.
Joel!
Are your JSR 308 canges involving java.lang.Class too?
Regards, Peter
On 12/12/2012 11:59 AM, Joel Borggrén-Franck wrote:
Hi all,
First, thanks all of you that are involved in this!
I agree with David here, lets split this up (for now) and do reflective objects
in the context of jep-149 and annotations separately.
As you may know there are even more annotation coming in with JSR 308
annotations on type (use), so I want to complete that work first and then do
the effort of reducing contention and overhead for both type and regular
annotations and also fixing up the behaviour for redefine/retransform class.
One other point to consider is that some of the fields in java/lang/reflect/
classes are known by the VM so not all changes in Java-land are actually
doable. Glancing over your patches very quickly I don't think you have done
anything to upset the VM, but then I am not an expert in this area.
Also, with the VM permgen changes we might have to rethink our assumptions in
order to reduce total overhead. For example as I understand it previously we
could just ship the same pointer into permgen for the annotations arrays, now
that isn't possible so we create a new copy of the array for every
Field/Method/Constructor instance. Perhaps there is some clever way of
eliminating those copies.
So while I think your patches generally makes sense, I think it is prudent to
delay this for annotations until all our new annotation features are in.
cheers
/Joel
On Dec 10, 2012, at 7:18 AM, David Holmes <david.hol...@oracle.com> wrote:
Hi Peter,
Sorry for the delay on this.
Generally your VolatileData and my ReflectionHelper are doing a similar job.
But I agree with your reasoning that all of the cached SoftReferences are
likely to be cleared at once, and so a SoftReference to a helper object with
direct references, is more effective than a direct reference to a helper object
with SoftReferences. My initial stance with this was very conservative as the
more change that is introduced the more uncertainty there is about the impact.
I say the above primarily because I think, if I am to proceed with this, I will
need to separate out the general reflection caching changes from the annotation
changes. There are a number of reasons for this:
First, I'm not at all familiar with the implementation of annotations at the VM
or Java level, and the recent changes in this area just exacerbate my ignorance
of the mechanics. So I don't feel qualified to evaluate that aspect.
Second, the bulk of the reflection caching code is simplified by the fact that
due to current constraints on class redefinition the caching is effectively
idempotent for fields/methods/constructors. But that is not the case for
annotations.
Finally, the use of synchronization with the annotations method is perplexing
me. I sent Joe a private email on this but I may as well raise it here - and I
think you have alluded to this in your earlier emails as well:
initAnnotationsIfNecessary() is a synchronized instance method but I can not
find any other code in the VM that synchronizes on the Class object's monitor.
So if this synchronization is trying to establish consistency in the face of
class redefinition, I do not see where class redefinition is participating in
the synchronization!
So what I would like to do is take your basic VolatileData part of the patch
and run with it for JEP-149 purposes, while separating the annotations issue so
they can be dealt with by the experts in that particular area.
I'm sorry it has taken so long to arrive at a fairly negative position, but I
need someone else to take up the annotations gauntlet and run with it.
Thanks,
David
On 3/12/2012 5:41 PM, Peter Levart wrote:
Hi David, Alan, Alexander and others,
In the meanwhile I have added another annotations space optimization to
the patch. If a Class doesn't inherit any annotations from a superclass,
which I think is a common case, it assigns the same Map instance to
"annotations" as well as "declaredAnnotations" fields. Previously - and
in the original code - this only happened for java.lang.Object and
interfaces.
Here's the updated webrev:
http://dl.dropbox.com/u/101777488/jdk8-tl/JEP-149/webrev.02/index.html
I have also rewritten the performance micro-benchmarks. With the
addition of repeating annotations, one performance aspect surfaces: when
asking for a particular annotation type on a Class and that annotation
is not present, the new repeating annotations support method
AnnotationSupport.getOneAnnotation asks for @ContainedBy meta-annotation
on the annotation type. This can result in an even more apparent
synchronization hot-spot with original code that uses synchronized
initAnnotationsIfNecessary(). This aspect is tested with the 3rd test.
Other 2 tests test the same thing as before but are more stable now,
since now they measure retrieval of 5 different annotation types from
each AnnotatedElement, previously they only measured retrieval of 1
which was very sensitive to HashMap irregularities (it could happen that
a particular key mapped to a bucket that was overloaded in one test-run
and not in another)...
Here're the new tests:
https://raw.github.com/plevart/jdk8-tl/JEP-149/test/src/test/ReflectionTest.java
And the corresponding results when run on an i7 CPU on Linux:
https://raw.github.com/plevart/jdk8-tl/JEP-149/test/benchmark_results_i7-2600K.txt
Regards, Peter
On 12/03/2012 02:15 AM, David Holmes wrote:
On 1/12/2012 4:54 AM, Alan Bateman wrote:
On 30/11/2012 18:36, Peter Levart wrote:
:
So, what do you think? What kind of tests should I prepare in addidion
to those 3 so that the patch might get a consideration?
I think this is good work and thanks for re-basing your patch. I know
David plans to do a detail review. I think it will require extensive
performance testing too, perhaps with some large applications.
Indeed I do plan a detailed review and have initiated some initial
performance tests.
I am also swamped but will try to get to the review this week - and
will also need to check the referenced annotations updates.
David
-Alan
