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

[Aleksey Shipilev]

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
>  - [x] Linux AArch64 server fastdebug, test does not fail after 10000x repetitions

Thanks! I noticed I had some debugging left-overs, removed them now.

The test completed 10000x iterations overnight on the machine where it used to fail 1/5 of the times, which tells me this thing works.

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PR Comment: https://git.openjdk.org/jdk/pull/26961#issuecomment-3231991528