Loading classes with many methods is very expensive

[Peter Levart]

Hi all,

I revamped the Class.getMethods() implementation so that it is faster 
for common cases and O(n) at the same time, which makes Martin's test 
happy (at least in part that measures getMethods() speed - the class 
loading / linkage in VM is a separate issue).

With the following test that loads all classes from rt.jar and calls 
getMethods() on each of them:

http://cr.openjdk.java.net/~plevart/jdk9-dev/Class.getMethods/GetAllRtMethods.java

And system property 'sun.reflect.noCaches=true' (so that we exercise the 
logic in every loop - not just 1st), original code prints:

19657 classes loaded in 1.987373401 seconds.
494141 methods obtained in 1.02493941 seconds.
494141 methods obtained in 0.905235658 seconds.
494141 methods obtained in 0.914434303 seconds.
494141 methods obtained in 0.887212805 seconds.
494141 methods obtained in 0.888929483 seconds.
494141 methods obtained in 0.883309141 seconds.
494141 methods obtained in 0.88341098 seconds.
494141 methods obtained in 0.897397146 seconds.
494141 methods obtained in 0.885677466 seconds.
494141 methods obtained in 0.895834176 seconds.

Patched code does the same about 10% faster:

19657 classes loaded in 2.084409717 seconds.
494124 methods obtained in 0.915928578 seconds.
494124 methods obtained in 0.785342465 seconds.
494124 methods obtained in 0.784852619 seconds.
494124 methods obtained in 0.793450205 seconds.
494124 methods obtained in 0.849915078 seconds.
494124 methods obtained in 0.77835511 seconds.
494124 methods obtained in 0.764144701 seconds.
494124 methods obtained in 0.754122383 seconds.
494124 methods obtained in 0.747961897 seconds.
494124 methods obtained in 0.7489937 seconds.

Martin's test prints on my computer with original code the following:

Base class load time: 177.80 ms
getDeclaredMethods: Methods: 65521, Total time: 35.79 ms, Time per 
method: 0.0005 ms
getMethods        : Methods: 65530, Total time: 50.15 ms, Time per 
method: 0.0008 ms
Derived class load time: 34015.70 ms
getDeclaredMethods: Methods: 65521, Total time: 33.82 ms, Time per 
method: 0.0005 ms
getMethods        : Methods: 65530, Total time: 8122.00 ms, Time per 
method: 0.1239 ms

And with patched code this:

Base class load time: 157.16 ms
getDeclaredMethods: Methods: 65521, Total time: 65.77 ms, Time per 
method: 0.0010 ms
getMethods        : Methods: 65530, Total time: 44.64 ms, Time per 
method: 0.0007 ms
Derived class load time: 33996.69 ms
getDeclaredMethods: Methods: 65521, Total time: 32.63 ms, Time per 
method: 0.0005 ms
getMethods        : Methods: 65530, Total time: 92.12 ms, Time per 
method: 0.0014 ms


Here's a webrev of the patch:

http://cr.openjdk.java.net/~plevart/jdk9-dev/Class.getMethods/webrev.01/

Patched code is simpler (65 lines gone) and I hope, easier to understand 
and change (I think a change in spec is coming in JDK9 which will handle 
abstract interface methods the same way as default, right Joel?)

I also took the liberty to eliminate some redundant array and 
Field/Method/Constructor copies. get[Method0,Field0,Counstuctor0] now 
return 'root' objects. Copying is performed in methods that call them 
and expose the objects to any code outside java.lang.Class. Also, 
findFields() and findMethods() don't do copying of Field/Method objects 
themselves, but rather live that to methods that call them. 
getInterfaces() method now delegates to getInterfaces(boolean copyArray) 
so that internally, not array copying is performed.

All 55 java/lang/reflect jtreg tests pass with this patch.


Regards, Peter