Hi Chris,
On 03/09/2016 12:07 PM, Chris Hegarty wrote:
Hi Peter,
On 9 Mar 2016, at 08:42, Peter Levart <peter.lev...@gmail.com> wrote:
Hi Chris,
While Attribute.Name.equals() should be comparably fast, what about
Attribute.Name.hashCode() ? Could you for example extend the
AvailableCharsetsCompare benchmark with a a @Setup method that constructs (via
Attributes.putValue(String, String)) a java.util.jar.Attributes instance with
available charsets as keys, then a @Benchmark method that traverses the
Attributes instance looking-up each available charset via the
Attributes.getValue(String) ... Just to see the relative amount of regression
that might be caused by constructing intermediate lowercase String(s)…
Just for clarification, the change in java.util.jar.Attributes has nothing to do
with the charsets. Attributes stores the individual attributes from the Jar
Manifest. There are only a relatively small number of standard Attributes [1].
When digging through old history to try to find out why java.util.jar.Attributes
was ever using ASCIICaseInsensitiveComparator, it was not clear that
performance was the motivation.
I guess looking-up a manifest attribute is not a performance critical
operation, you are right.
It seemed to be a knock on effect of the
use of the comparator ( which was trying to avoid the continuous allocation
cost to toLowerCase during comparisons ). I don’t think this code is
particularly
performance sensitive, and especially not hashCode.
The effects of equals() vs. hashCode() on the lookup performance
(Attributes.getValue()) is approximately the same. As keys of HashMap
are Name objects and each lookup constructs new Name object, there's
typically one Name.hashCode() invocation and one Name.equals()
invocation per lookup (hashCode caching doesn't help here).
Maybe a benchmark with a number of standard Jar file attributes would make
sense?
Right. Let me assist you with creating it. Stay tuned...
Regards, Peter
-Chris.
[1]
http://docs.oracle.com/javase/8/docs/technotes/guides/jar/jar.html#Main_Attributes
