On 12/17/12 7:36 AM, Peter Levart wrote:
Hi David and others,
Here's a patch that eliminates one of two fields in java.lang.Class,
related to caching enum constants:
http://dl.dropbox.com/u/101777488/jdk8-tl/JEP-149.enum/webrev.01/index.html
It does it by moving one field to a subclass of HashMap, which is
referenced by a remaining field that serves two different
purposes/stages of caching.
Your observation of merging the enumConstants and enumConstantDirectory
is a good one. I see that caching of enumConstantDirectory is
important as it's used by EnumMap and EnumSet whose performance is
critical (specified with constant time operations). I'm unsure about
Class.getEnumConstants whether it's performance critical and worths the
complexity of your proposed fix (the enumData field of two types). If a
class has cached an enumConstantDirectory, Class.getEnumConstants can
return a clone of its values().
Anyone knows how Class.getEnumConstants is commonly used and needs to be
performant? I suspect it's more typical to obtain the list of enum
constants statistically (calling Enum.values()) than reflectively.
Mandy
These are the results of a micro-benchmark that exercises public API
that uses the internal j.l.Class API regarding enum constants:
enum MyEnum { ONE, TWO, THREE, FOUR, FIVE, SIX, SEVEN, EIGHT, NINE, TEN }
EnumSet.noneOf(MyEnum.class): 300_000_000 loops
MyEnum.valueOf(String): 30_000_000 loops * 10 calls for different names
** Original JDK8 code
Executing: /home/peter/Apps64/jdk1.8.0-jdk8-tl/bin/java -Xmx4G -cp
../out/production/test test.EnumTest reference
EnumSet.noneOf(Class): 351610312 340302968 339893333 339774384
339750612 339558414 339547022 339621595
MyEnum.valueOf(String): 935153830 897188742 887541353 960839820
886119463 885818334 885827093 885752461
EnumSet.noneOf(Class): 339552678 339469528 339513757 339451341
339512154 339511634 339664326 339793144
** patched java.lang.Class
Executing: /home/peter/Apps64/jdk1.8.0-jdk8-tl/bin/java -Xmx4G -cp
../out/production/test -Xbootclasspath/p:../out/production/jdk
test.EnumTest
EnumSet.noneOf(Class): 351724931 339286591 305082929 305042885
305058303 305044144 305073463 305049604
MyEnum.valueOf(String): 955032718 908534137 891406394 891506147
891414312 893652469 891412757 891409294
EnumSet.noneOf(Class): 414044087 406904161 406788898 406839824
406765274 406815728 407002576 406779162
The slow-down of about 20% (last line) is presumably a consequence of
another in-direction to obtain shared enum constants array when there
is already a Map in place. It is still fast though (300M EnumSet
instances / 0.4 s).
Here's the source of the micro-benchmark:
https://raw.github.com/plevart/jdk8-tl/JEP-149.enum/test/src/test/EnumTest.java
I don't know what's more important in this occasion. A small space
gain (8 or 4 bytes per j.l.Class instance) or a small performance gain
(20%).
Regards, Peter
