RFR: 8244624: Improve handling of JarFile META-INF resources

[Claes Redestad]

Hi Martin,

On 2020-05-10 21:53, Martin Buchholz wrote:
> Thanks for improving the jar/zip code.

thanks!

> I wish I had more time to do the same.
> My own superficial review only adds one small suggestion:
> add a comment as to why isSignatureRelated never hits a negative index
> exception.

Yes, it's a bit subtle and deserves a comment.

> I still like my ancient "ASCII trick" comment.

Google "oldest ASCII trick in the book" and the first hit is an article
about this trick (or well, the inverse - but it still counts!). :-)

Lance only suggested we clarify what that trick is - hope you're OK with
that:

http://cr.openjdk.java.net/~redestad/8244624/open.02/

/Claes

> 
> On Thu, May 7, 2020 at 2:34 PM Claes Redestad <claes.redestad at oracle.com> wrote:
>>
>> Hi,
>>
>> currently during ZipFile creation, we create an int[] array of pointers
>> to META-INF entries. These are then retrieved from three different
>> places in JarFile.
>>
>> However, JarFile is only interested in some combination a few things:
>> the existence of and name of the META-INF/MANIFEST file, the existence
>> of and the names of various signature related files, i.e., files in
>> META-INF that have a suffix such as .EC, .SF, .RSA and .DSA
>>
>> Refactoring the contract between JarFile and ZipFile means we can filter
>> out such entries that we're not interested when opening the file, and
>> also remove the need to create the String for each entries unless we
>> actually want them:
>>
>> Bug:    https://bugs.openjdk.java.net/browse/JDK-8244624
>> Webrev: http://cr.openjdk.java.net/~redestad/8244624/open.00/
>>
>> This reduces retained footprint of Jar-/ZipFile by slimming down or
>> removing the Source.metanames array entirely, and a significant speed-up
>> in some cases.
>>
>> In the provided microbenchmark, getManifestFromJarWithManifest and
>> getManifestFromJarWithSignatureFiles doesn't call
>> JUZFA.getMetaInfEntryNames but still see small (~5%) speed-up decrease
>> in allocations.
>>
>> getManifestFromJarWithNoManifest exercise JUZFA.getMetaInfEntryNames in
>> the baseline, and now calls JUZFA.getManifestName. Result is a 1.25x
>> speed-up and 30% reduction in allocations. While unrealistic (most JARs
>> have a META-INF/MANIFEST.MF), this speed-up will translate to a few
>> places - such as when loading classes from potentially-signed JAR files.
>>
>> Testing: tier1-2
>>
>> Thanks!
>>
>> /Claes