Proxy.isProxyClass scalability (original) (raw)

Peter Levart peter.levart at gmail.com
Wed Apr 10 12:35:24 UTC 2013

Hi Alan,

I have prepared new webrev of the patch rebased to current tip of jdk8/tl repo:

https://dl.dropboxusercontent.com/u/101777488/jdk8-tl/proxy/webrev.04/index.html

I noticed there were quite a few changes to the j.l.r.Proxy in the meanwhile regarding new security checks. But @CallerSensitive changes seem not to have been pushed yet.

Anyway, I have also simplified the caching logic a bit so that it's now easier to reason about it's correctness. I have re-run the performance benchmarks that are still very favourable:

https://raw.github.com/plevart/jdk8-tl/proxy/test/proxy_benchmark_results.txt

Proxy.getProxyClass(): is almost 15x faster single-threaded with same or even slightly better scalability Proxy.isProxyClass() == true: is about 9x faster for single-threaded execution and much more scalable Proxy.isProxyClass() == false: is about 1600x faster single-threaded and infinitely scalable Annotation.equals(): is 1.6x faster single-threaded and much more scalable

I also devised an alternative caching mechanism with scalability in mind which uses WeakReferences for keys (for example ClassLoader) and values (for example Class) that could be used in this situation in case adding a field to ClassLoader is not an option:

https://github.com/plevart/jdk8-tl/blob/proxy/test/src/test/WeakCache.java

Regards, Peter

On 01/28/2013 05:13 PM, Peter Levart wrote:

Hi Alan,

I prepared the variant with lazy initialization of ConcurrentHashMaps per ClassLoader and performance measurements show no differences. So here's this variant: * http://dl.dropbox.com/u/101777488/jdk8-tl/proxy/webrev.03/index.html I also checked the ClassLoader layout and as it happens the additional pointer slot increases the ClassLoader object size by 8 bytes in both addressing modes: 32bit and 64bit. But that's a small overhead compared to for example the deep-size of AppClassLoader at the beginning of the main method: 14648 bytes (32bit) / 22432 bytes (64bit). Regards, Peter On 01/28/2013 01:57 PM, Peter Levart wrote: On 01/28/2013 12:49 PM, Alan Bateman wrote:

On 25/01/2013 17:55, Peter Levart wrote:

: The solution is actually very simple. I just want to validate my reasoning before jumping to implement it: - for solving scalability of getProxyClass cache, a field with a reference to ConcurrentHashMap<List, Class<? extends_ _Proxy>> is added to j.l.ClassLoader - for solving scalability of isProxyClass, a field with a reference to ConcurrentHashMap<Class<? extends Proxy>, Boolean> is added to j.l.ClassLoader I haven't had time to look very closely as your more recent changes (you are clearly doing very good work here). The only thing I wonder if whether it would be possible to avoid adding to ClassLoader. I can't say what percentage of frameworks and applications use proxies but it would be nice if the impact on applications that don't use proxies is zero. Hi Alan, Hm, well. Any application that uses run-time annotations, is implicitly using Proxies. But I agree that there are applications that don't use either. Such applications usually don't use many ClassLoaders either. Applications that use many ClassLoaders are typically application servers or applications written for modular systems (such as OSGI or NetBeans) and all those applications are also full of runtime annotations nowadays. So a typical application that does not use neither Proxies nor runtime annotations is composed of bootstrap classloader, AppClassLoader and ExtClassLoader. The ConcurrentHashMap for the bootstrap classloader is hosted by j.l.r.Proxy class and is only initialized when the j.l.r.Proxy class is initialized - so in this case never. The overhead for such applications is therefore an empty ConcurrentHashMap instance plus the overhead for a pointer slot in the ClassLoader object multiplied by the number of ClassLoaders (typically 2). An empty ConcurrentHashMap in JDK8 is only pre-allocating a single internal Segment: java.util.concurrent.ConcurrentHashMap at 642b6fc7(48 bytes) { keySet: null values: null hashSeed: int segmentMask: int segmentShift: int segments: java.util.concurrent.ConcurrentHashMap$Segment[16]@8e1dfb1(80 bytes) { java.util.concurrent.ConcurrentHashMap$Segment at 2524e205(40 bytes) { sync: java.util.concurrent.locks.ReentrantLock$NonfairSync at 17feafba(32 bytes) { exclusiveOwnerThread: null head: null tail: null state: int }->(32 deep bytes) table: java.util.concurrent.ConcurrentHashMap$HashEntry[2]@1c3aacb4(24 bytes) { null null }->(24 deep bytes) count: int modCount: int threshold: int loadFactor: float }->(96 deep bytes) null null null null null null null null null null null null null null null }->(176 deep bytes) keySet: null entrySet: null values: null }->(224 deep bytes) ...therefore the overhead is approx. 224+4 = 228 bytes (on 32 bit pointer environments) per ClassLoader. In typical application (with 2 ClassLoader objects) this amounts to approx. 456 bytes. Is 456 bytes overhead too much? If it is, I could do lazy initialization of per-classloader CHM instances, but then the fast-path would incur a little additional penalty (not to be taken seriously though). Regards, Peter P.S. I was inspecting the ClassValue internal implementation. This is a very nice piece of Java code. Without using any Unsafe magic, it provides a perfect performant an scalable map of lazily initialized independent data structures associated with Class instances. There's nothing special about ClassValue/ClassValueMap that would tie it to Class instances. In fact I think the ClassValueMap could be made generic so it could be reused for implementing a ClasLoaderValue, for example. This would provide a more performant and scalable alternative to using WeakHashMap<ClassLoader, ...> wrapped by synchronized wrappers for other uses. If anything like that happens in the future, the proposed patch can be quickly adapted to using that infrastructure instead of a direct reference in the ClassLoader. -Alan

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