Peter, Which hotspot algorithm is the one you identified as slow? Would that be for loading the class or for Class.getMethods?
thanks, Karen On Oct 23, 2014, at 9:37 AM, Peter Levart wrote: > On 10/23/2014 01:57 AM, Stanimir Simeonoff wrote: >> Class.java can easily be improved by adding an auxiliary HasMap<String, >> Integer/int[]> indexing the position in the array by name and then checking >> only few overloaded signatures in case of a match. >> The auxiliary map can be deployed only past some threshold of methods, so >> it should not affect the common case. >> >> Alternatively sorting the array and using binary search is quite trivial to >> implement as well. > > Java Class.getMethods() implementation is complicated by the fact that, > although not specified, the order of methods in returned array is important. > Once it changed, if I remember correctly, and broke many programs, so it had > to be restored... > > Peter > >> >> Btw, really nice benchmark. >> >> Stanimir >> >> >> On Thu, Oct 23, 2014 at 1:53 AM, Martin Buchholz <marti...@google.com> >> wrote: >> >>> Here at Google we have both kinds of scalability problems - loading classes >>> from a classpath with 10,000 jars, and loading a single class file packed >>> with the maximal number of methods. This message is about the latter. >>> >>> If you have a class with ~64k methods with a superclass that also has ~64k >>> methods, class loading that single class will cost you ~30sec and calling >>> Class.getMethods another ~10sec. Both are unacceptably slow. I think both >>> are due to O(N^2) algorithms, the first in hotspot, and the second in >>> Class.java. >>> >>> I have the start of a fix for Class.java, but it makes the common case >>> slower. A really good fix is harder to find. In general, I think >>> Class.java could benefit from some performance-oriented rework. Is anyone >>> else working on class loading performance, especially in hotspot? >>> >>> Here's the benchmark (that could perhaps be integrated into openjdk even >>> without a fix) >>> >>> >>> http://cr.openjdk.java.net/~martin/webrevs/openjdk9/Class.getMethods-benchmark/test/java/lang/Class/getMethods/ManyMethodsBenchmark.java.html >>> >>> Base class load time: 186.44 ms >>> getDeclaredMethods: Methods: 65521, Total time: 43.27 ms, Time per method: >>> 0.0007 ms >>> getMethods : Methods: 65530, Total time: 60.82 ms, Time per method: >>> 0.0009 ms >>> Derived class load time: 33440.13 ms >>> getDeclaredMethods: Methods: 65521, Total time: 39.71 ms, Time per method: >>> 0.0006 ms >>> getMethods : Methods: 65530, Total time: 11582.54 ms, Time per >>> method: 0.1768 ms >>> >
