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

[Jason Zaugg]

> 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.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3853/files
  - new: https://git.openjdk.java.net/jdk/pull/3853/files/c9758c58..9106096e

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3853&range=04
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3853&range=03-04

  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3853.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3853/head:pull/3853

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