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

[Brian Burkhalter]

On Wed, 27 Aug 2025 14:05:14 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
>  - [ ] Linux AArch64 server fastdebug, test does not fail after 1000x repetitions

This looks all right to me. I ran 500 repeats on each of Linux aarch64 and x64 in our CI and there were no failures. I did increment the reviewer count to two however so one more approval will be needed.

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Marked as reviewed by bpb (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/26961#pullrequestreview-3162263667