RFR: 8333783: java/nio/channels/FileChannel/directio/DirectIOTest.java is unstable with AV software [v2]

[Brian Burkhalter]

On Thu, 28 Aug 2025 05:55:20 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> This test routinely fails on our instances that have AV software enabled: that software apparently reads the file in background on access, which trips the very sensitive "is file in cache" test. It looks like there is a reliable way to mitigate this by keeping the file open, and attempting the (read|write)+check several times, with cache flush in between.
>> 
>> This is not perfect, but works in practice. Second attempt seems to work in >99% of the cases, we are doing 3 attempts to make test extra reliable.
>> 
>> Additional testing:
>>  - [x] Linux AArch64 server fastdebug; sensitivity check: dropped `DIRECT` from the test, test starts failing immediately
>>  - [x] Linux AArch64 server fastdebug, test does not fail after 100x repetitions
>>  - [x] Linux AArch64 server fastdebug, test does not fail after 10000x repetitions
>
> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove unnecessary changes

Still looks fine.

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Marked as reviewed by bpb (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/26961#pullrequestreview-3165428425