RFR: 8294437: java/nio/channels/FileChannel tests slow on Windows [v2]

[Brian Burkhalter]

On Thu, 29 Sep 2022 14:30:21 GMT, Daniel Jeliński <djelinski at openjdk.org> wrote:

>> Please review this test-only change that improves the execution speed of a few FileChannel tests:
>> - Transfer2GPlus, Transfer4GBFile, and TransferTo6GBFile were modified to use sparse files. Their speed is now consistent across platforms, provided that the platform / filesystem supports sparse files.
>> - LargeMapTest was rewritten to use sparse files, and to more precisely target the issue it was written to detect. In my tests it still crashed with EXCEPTION_ACCESS_VIOLATION when JDK-8286637 was reverted.
>> - MapTest: repetition was removed from `testForce` method; I'm not sure what issues it was supposed to catch, but at far as I can tell, it was only triggering timeouts, see [JDK-8289526](https://bugs.openjdk.org/browse/JDK-8289526), [JDK-8224480](https://bugs.openjdk.org/browse/JDK-8224480)
>
> Daniel Jeliński has updated the pull request incrementally with seven additional commits since the last revision:
> 
>  - Remove intermittently failing deletes
>  - reintroduce deleteOnExit
>  - rewrite testToWritableByteChannel without using file output
>  - Migrate Transfer4GBFile to nio
>  - Implement createSparseTempFile
>  - Use RandomFactory to generate random bytes
>  - Update copyright year

test/jdk/java/nio/channels/FileChannel/Transfer2GPlus.java line 140:

> 138: 
> 139:             long n;
> 140:             if ((n = srcCh.transferTo(0, LENGTH, wbc)) < LENGTH)

The contract of `FileChannel::transferTo` does not guarantee that all bytes are transferred:

```An invocation of this method may or may not transfer all of the requested bytes [...]```.

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PR: https://git.openjdk.org/jdk/pull/10464