RFR: 8265448: (zipfs): Reduce read contention in ZipFileSystem [v5]

[Lance Andersen]

On Fri, 7 May 2021 03:10:32 GMT, Jason Zaugg <jzaugg at openjdk.org> wrote:

>> If the given Path represents a file, use the overload of read defined
>> in FileChannel that accepts an explicit position and avoid serializing
>> reads.
>> 
>> Note: The underlying NIO implementation is not required to implement
>> FileChannel.read(ByteBuffer, long) concurrently; Windows still appears
>> to lock, as it returns true for NativeDispatcher.needsPositionLock.
>> 
>> 
>> On MacOS X, the enclosed benchmark improves from:
>> 
>> 
>> Benchmark                    Mode  Cnt   Score   Error  Units
>> ZipFileSystemBenchmark.read  avgt   10  75.311 ? 3.301  ms/op
>> 
>> 
>> To:
>> 
>> 
>> Benchmark                    Mode  Cnt   Score   Error  Units
>> ZipFileSystemBenchmark.read  avgt   10  12.520 ? 0.875  ms/op
>
> Jason Zaugg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   [zipfs] Add missing check-failed exception to position/read test
>   
>   This appears to have been omitted when this test was added.
>   To avoid false error reports, the condition must deal with the
>   edge case of zero-length entries, for which read will return -1.

Mach5 jdk-tier1, jdk-tier, jdk-tier3 completed successfully

-------------

Marked as reviewed by lancea (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/3853