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

[Daniel Jeliński]

On Wed, 28 Sep 2022 19:01:45 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/MapTest.java line 95:
> 
>> 93:             t1 = System.nanoTime();
>> 94:             out.printf("Exceptions: done in %d ns (%d ms) %n",
>> 95:                     t1 - t0, TimeUnit.NANOSECONDS.toMillis(t1 - t0));
> 
> Are you planning to leave all these timestamps in the output? I can't tell if they are left over from your testing or intentional.

Yeah, I wanted to leave them here; they don't take up much space, and are very useful when trying to figure out why the tests are slow.

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