Improving perf of FileChannel.transferTo() on Windows

[Martin Sawicki (MS OPEN TECH)]

Hello
We're proposing an improvement to the OpenJDK which markedly improves the performance of the FileChannel.transferTo API when running on Windows.
We have the code figured out and tested internally. Our webrev patch is available here:
https://openjdkcontrib.blob.core.windows.net/transferto/webrev-20140918.zip

The crux of the change is a Windows implementation of transferTo() that uses the Win32 TransmitFile function to do the copy on a shorter code path in the kernel.

As for activating this optimization, we're proposing the conservative approach of keeping it off by default and adding a command line argument to activate it:
-Dwindows.enableFastFileTransfer=true | false

(IMHO though, it'd be great to eventually just have it on by default).

We'd appreciate a review and acceptance of this improvement.

Best regards

Martin Sawicki (and Kirk Shoop, and Valeriy Kopylov)
Microsoft Open Technologies, Inc.
A subsidiary of Microsoft Corp.

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