At end...
On 12/18/2012 07:50 PM, Remi Forax wrote:
On 12/18/2012 10:18 AM, Peter Levart wrote:
On 12/17/2012 11:39 PM, Remi Forax wrote:
On 12/17/2012 11:14 PM, Peter Levart wrote:
On 12/17/2012 10:26 PM, Mandy Chung wrote:
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.
Hi Mandy,
public Class.getEnumConstants() is a reflection mirror of
SomeEnum.values(). It returns a defensive copy of the constants
array. The primary place for Enum constants is in a private static
final $VALUES field, generated by compiler in each Enum subclass.
But that I think is not part of specification, so for internal
usage (as far as I have managed to find out only in the
constructors of EnumSet and EnumMap), the package-private
Class.getEnumConstantsShared() is used which obtains a copy of the
array by calling SomeEnum.values() and than caches is.
The Class.enumConstantDirectory() on the other hand is an internal
package-private method that returns a shared/cached Map<String, T>,
which is used internally to implement SomeEnum.valueOf(String) and
Enum.valueOf(Class, String) static methods.
Both package-private methods must be fast.
Regards, Peter
for what it worth, I'm the guy behind the patch of bug 6276988 (it
was before OpenJDK was setup BTW),
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6276988
and for the little story, I need that patch because I was developing
an Eclipse plugin that uses EnumSet to represent the possible
completion values.
So to answer to Mandy, this application needs really fast EnumSet
creation thus really fast getEnumConstantShared() because the
EnumSets was created as user types code.
Hi Rémi,
is 600M EnumSets / sec good enough for a fast typist?
The eclipse plugin uses is a LR parser (a GLR exactly) which has the
stupid property that it can change the whole parse tree if you just
add one character.
Also i'm maybe wrong but, if you test with several different 'enum
classes', you should see a slowdown.
Rémi
You're right. I modified the test to use 5 different enum classes
interchangeably in a loop:
https://raw.github.com/plevart/jdk8-tl/JEP-149.enum/test/src/test/EnumTest.java
The slowdown of EnumSet.noneOf() compared to original code was more
apparent - about 50% when there's an array assigned to enumData field
and more than 60% when there's already an EnumData object holding the
array reference. MyEnum.valueOf(String) seems to be unaffected - more
cycles spent elsewhere in the code-path to be significant.
When I changed the "if (enumData instanceof Enum[])" with "if (enumData
!= null)", the slowdown of EnumSet.noneOf() was less apparent - about
24% when there's an array assigned to enumData and about 44% when
there's EnumData object. MyEnum.valueOf(String) shows the same performance.
So in order to affect the performance as little as possible, I devised a
more direct approach without instanceof checks and casts. Here it is:
http://dl.dropbox.com/u/101777488/jdk8-tl/JEP-149.enum/webrev.02/index.html
With this change, EnumSet.noneOf() is only about 12% slower than
original code and MyEnum.valueOf(String) performs the same. This code
has a space overhead of an extra object with two fields, but it is
expected that the number of enum classes compared to non-enum classes is
small and the reduction of a field in the java.lang.Class pays off. Even
though this is a single field and it might not shrink (not every but
approx. half of all?) java.lang.Class object (s) on 32bit architectures
due to alignment constraints, it presents an opportunity for shrinkage
when other individual fields in java.lang.Class are similarly removed.
One such opportunity presents the 2+1 remaining fields used for caching
annotations.
I understand that contributions to JEP-149 are closed already, but I
post this here for any future reference.
Regards, Peter
