RFR JDK-8172921: Zip filesystem performance improvement and code cleanup

[Xueming Shen]

Hi,

Please review the following changes for zipfs implementation.

issue: https://bugs.openjdk.java.net/browse/JDK-8172921
webrev: http://cr.openjdk.java.net/~sherman/8172921/webrev/


javac has moved to use zipfs (instead of ZipFile) to access jar files in 
jdk9. Here are
some changes to improve the performance of access time and footprint 
(reduce the
unnecessary object allocation ...) The improvement has been measured by 
the jmh
benchmark test as

http://cr.openjdk.java.net/~sherman/8172921/MyBenchmark.java

with the benchmark sores (before-OLD/after-NEW) at:

http://cr.openjdk.java.net/~sherman/8172921/scores


The main change is to change the internal directory path representation 
from the
zip specific format (directory name ends with "/", "/dir/" for directory 
".dir" for
example) to the "normalized" form with the tailing "/", which reduces 
the back and
forth  conversion between the normal "unix style" path and the "zip 
style" path when
doing path creation, path lookup and entry access, which also simplified 
the entry
lookup logic.

We are seeing pretty good performance improvement.

There is another change, which involves the API change, for the 
"non-existing" path
look up (which shows pretty bad numbers as ZFS_ExistsNG"), is not 
included in this
patch. I hope we can address that as well in jdk9, but probably in 
another patch.

Thanks,
Sherman