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
