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

[Aleksey Shipilev]

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

-------------

Commit messages:
 - Tunable try count
 - Fix

Changes: https://git.openjdk.org/jdk/pull/26961/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26961&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8333783
  Stats: 110 lines in 2 files changed: 70 ins; 23 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/26961.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26961/head:pull/26961

PR: https://git.openjdk.org/jdk/pull/26961