RFR: 8301873: Avoid string decoding in ZipFile.Source.getEntryPos [v4]

[Eirik Bjorsnos]

On Tue, 7 Feb 2023 13:23:26 GMT, Eirik Bjorsnos <duke at openjdk.org> wrote:

>> After finding a hash match, getEntryPos needs to compare the lookup name up to the encoded entry name in the CEN. This comparison is done by decoding the entry name into a String. The names can then be compared using the String API. This decoding step adds a significat cost to this method.
>> 
>> This PR suggest to update the string comparison such that in the common case where  both the lookup name and the entry name are encoded in ASCII-compatible UTF-8,  decoding can be avoided and the byte arrays can instead be compared direcly. 
>> 
>> ZipCoder is updated with a new method to compare a string with an encoded byte array range.  The default implementation decodes to string (like the current code), while the UTF-8 implementation uses JavaLangAccess.getBytesNoRepl to get the  bytes. Both methods thes uses Arrays.mismatch for comparison with or without matching trailing slashes. 
>> 
>> Additionally, this PR suggest to make the following updates to getEntryPos:
>> 
>> - The try/catch for IAE is redundant and can be safely removed. (initCEN already checks this and will throws IAE for invalid UTF-8). This seems to give a 3-4% speedup on micros)
>> - A new test InvalidBytesInEntryNameOrComment is a added to verify that initCEN does in fact reject invalid UTF-8 in CEN file names and comments. (I found no existing test coverage for this)
>> - The recursion when looking for "name/" matches is replaced with iteration. We keep track of any "name/" match and return it at the end of the search. (I feel this is easier to follow and it also gives a ~30% speedup for addSlash lookups with no regression on regular lookups)
>> 
>> (My though is that including these additional updates in this PR might reduce reviewer overhead given that it touches the exact same code. I might be wrong on this, please advise :)
>> 
>> I'm seeing a ~17% saving on the micro ZipFileGetEntry.getEntryHit (modified to use xalan.jar):
>> 
>> Baseline:
>> 
>> Benchmark                             (size)  Mode  Cnt    Score   Error  Units
>> ZipFileGetEntry.getEntryHit              512  avgt   15   74.941 ± 1.004  ns/op
>> ZipFileGetEntry.getEntryHit             1024  avgt   15   84.943 ± 1.320  ns/op
>> ZipFileGetEntry.getEntryHitUncached      512  avgt   15  120.371 ± 2.386  ns/op
>> ZipFileGetEntry.getEntryHitUncached     1024  avgt   15  126.128 ± 1.075  ns/op
>> ZipFileGetEntry.getEntryMiss             512  avgt   15   23.818 ± 0.838  ns/op
>> ZipFileGetEntry.getEntryMiss            1024  avgt   15   29.762 ± 5.998  ns/op
>> ZipFileGetEntry.getEntryMissUncached     512  avgt   15   59.405 ± 0.545  ns/op
>> ZipFileGetEntry.getEntryMissUncached    1024  avgt   15   71.840 ± 2.455  ns/op
>> ZipFileGetEntry.getEntrySlash            512  avgt   15  135.621 ± 4.341  ns/op
>> ZipFileGetEntry.getEntrySlash           1024  avgt   15  134.190 ± 2.141  ns/op
>> 
>> 
>> 
>> PR:
>> 
>> 
>> Benchmark                             (size)  Mode  Cnt    Score   Error  Units
>> ZipFileGetEntry.getEntryHit              512  avgt   15   62.267 ± 1.329  ns/op
>> ZipFileGetEntry.getEntryHit             1024  avgt   15   72.916 ± 2.428  ns/op
>> ZipFileGetEntry.getEntryHitUncached      512  avgt   15  101.630 ± 1.154  ns/op
>> ZipFileGetEntry.getEntryHitUncached     1024  avgt   15  113.161 ± 0.502  ns/op
>> ZipFileGetEntry.getEntryMiss             512  avgt   15   23.003 ± 1.191  ns/op
>> ZipFileGetEntry.getEntryMiss            1024  avgt   15   23.236 ± 1.114  ns/op
>> ZipFileGetEntry.getEntryMissUncached     512  avgt   15   56.781 ± 1.505  ns/op
>> ZipFileGetEntry.getEntryMissUncached    1024  avgt   15   67.767 ± 1.963  ns/op
>> ZipFileGetEntry.getEntrySlash            512  avgt   15   73.745 ± 2.717  ns/op
>> ZipFileGetEntry.getEntrySlash           1024  avgt   15   75.784 ± 1.051  ns/op
>> 
>> 
>> To assess the impact on startup/warmup, I made a main method class which measures the total time of calling ZipFile.getEntry for all entries in the 109 JAR file dependenies of spring-petclinic. The shows a nice improvement (time in micros):
>> 
>> 
>> Percentile Baseline Patch
>> 50 %          23155 21149
>> 75 %          23598 21454
>> 90 %          23989 21691
>> 95 %          24238 21973
>> 99 %          25270 22446
>> STDEV           792   549
>> Count           500   500
>
> Eirik Bjorsnos has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 20 additional commits since the last revision:
> 
>  - Merge branch 'master' into getentrypos-prefixmatch
>  - Fix incorrect offset for the CEN "length of extra field". Fixed spelling of "invalid".
>  - Spelling fix in test data for non-ascii latin1 string
>  - Replace new shared secret with using getBytesNoRepl in UTF8ZipCoder.compare. Add a test case for UTF-8 encoded entry name which is latin1, but not ASCII
>  - Rename test to InvalidBytesInEntryNameOrComment
>  - Adjust whitespace
>  - Some minor improvements to code comments
>  - Micros seem to indicate that the range checks in Arrays.mismatch might have as much as 5% regression
>  - Move String/byte[] comparison into ZipCoder. Change the default implementation to decode to string for comparison instead of encoding to bytes, this seems safer. Revert some changes from previous commits to parameters in the hasTrailingSlash method.
>  - ByteBuffers for reading ZIP files must be little-endian
>  - ... and 10 more: https://git.openjdk.org/jdk/compare/4399bd8c...06047377

I have reproduced this by running testUnicodeManyEntries in a while loop. Smells of hash collisions or System.currentTimeMillis issues.

I'm marking this PR as draft while we investigate this issue.

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PR: https://git.openjdk.org/jdk/pull/12290