Hello,
Recently I stumbled upon the scalability problem of
j.l.r.Proxy.isProxyClass(Class) method when trying to find-out why the
equals() method of annotations is not scalable. The reason is that
j.l.r.Proxy uses a single synchronized wrapper around WeakHashMap to
keep track of proxy classes in order to implement isProxyClass method:
244 /** set of all generated proxy classes, for isProxyClass
implementation */
245 private static Map<Class<?>, Void> proxyClasses =
246 Collections.synchronizedMap(new WeakHashMap<Class<?>, Void>());
631 public static boolean isProxyClass(Class<?> cl) {
632 if (cl == null) {
633 throw new NullPointerException();
634 }
635
636 return proxyClasses.containsKey(cl);
637 }
In the discussion on the cuncurrency-interest list:
*
http://cs.oswego.edu/pipermail/concurrency-interest/2013-January/010642.html
...it was indicated that other places in JDK besides the annotation's
equals() method suffer from this scalability bottleneck, mainly in the
field of serialization, RMI and JMX.
With the help from this discussion, I prepared a possible fix which I'm
proposing here:
http://dl.dropbox.com/u/101777488/jdk8-tl/isProxyClass/webrev.01/index.html
The fix drops usage of synchronized wrapper and WeakHashMap and replaces
them with a ClassValue and a little ThreadLocal trick to initialize it.
The ThreadLocal trick could be replaced with a simple static variable
guarded by a synchronized block if desired.
I have some results from a micro-benchmark that exercises the
annotation's equals method. The results were obtained on two different
systems:
* https://raw.github.com/plevart/jdk8-tl/proxy/test/benchmark_results.txt
The benchmark sources:
*
https://github.com/plevart/jdk8-tl/blob/proxy/test/src/test/AnnotationEqualsTest.java
*
https://github.com/plevart/micro-bench/blob/master/src/si/pele/microbench/TestRunner.java
Thanks to Aleksey Shipilev for showing me the obvious pitfalls when
designing a micro-benchmark. I hope this time it does the job correctly...
What do you thik? Should I file a RFE first?
Regards, Peter
