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

[Daniel Jeliński]

On Wed, 28 Sep 2022 19:01:14 GMT, Alan Bateman <alanb 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)
>
> test/jdk/java/nio/channels/FileChannel/LargeMapTest.java line 64:
> 
>> 62:         try (FileChannel fc = FileChannel.open(p, CREATE_NEW, SPARSE, WRITE)) {
>> 63:             fc.position(BASE);
>> 64:             Random r = new Random(System.nanoTime());
> 
> It might not matter here but we usually use RandomFactory to allow for reproducibility in the event of test failure.

Thanks for the hint! It shouldn't matter here, but I'll change it.

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