RFR: 8351601: [JMH] test UnixSocketChannelReadWrite failed for 2 threads config

[Volkan Yazici]

On Tue, 25 Mar 2025 08:31:02 GMT, Michael McMahon <michaelm at openjdk.org> wrote:

>>> > > Seems like the only explanation for why that is happening is someone cleaning out /tmp while the test is running
>>> > 
>>> > 
>>> > @Michael-Mc-Mahon No, the reason for the failure is multiple threads creating a Unix socket in the very same `tempDir`, and then trying to delete the `tempDir`. See the following execution flow involving multiple threads:
>>> > ```
>>> > 1. `tempDir` is statically assigned during class initialization (say `/tmp/readWriteTest2414375588689416060`)
>>> > 
>>> > 2. `Thread1` runs `beforeRun()`, which creates the Unix socket `/tmp/readWriteTest2414375588689416060/1`
>>> > 
>>> > 3. `Thread2` runs `beforeRun()`, which creates the Unix socket `/tmp/readWriteTest2414375588689416060/2`
>>> > 
>>> > 4. Both `Thread1` and `Thread2` runs `afterRun()` in parallel
>>> > 
>>> > 5. `Thread1` runs `Files.delete(/tmp/readWriteTest2414375588689416060/1)` and succeeds
>>> > 
>>> > 6. `Thread2` runs `Files.delete(/tmp/readWriteTest2414375588689416060/2)` and succeeds
>>> > 
>>> > 7. `Thread1` runs `Files.delete(/tmp/readWriteTest2414375588689416060)` and succeeds (since both `/1` and `/2` socket files are removed above, and, hence, the directory is empty)
>>> > 
>>> > 8. `Thread2` runs `Files.delete(/tmp/readWriteTest2414375588689416060)` and fails, since the directory has already been deleted above
>>> > ```
>>> > 
>>> > 
>>> >     
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>>> >   
>>> > Ideally, `tempDir` deletion should be performed by a single thread. But replacing `Files::delete` with `Files::deleteIfExists` also does the job, at a lower cost.
>>> 
>>> What would happen then if thread1 completes before thread2 starts? Maybe, we _should_ delete the directory in a separate block, executed in a single thread at the every end. Is there a variant of the @teardown() annotation which executes at the end of the test?
>> 
>> maybe the directory could be created and deleted in separate Setup/Teardown(Level.Trial) invocations ?
>
>> @Michael-Mc-Mahon, I use dedicated temporary directory per socket in [cabb414](https://github.com/openjdk/jdk/commit/cabb4145759a982ba32e9ade82066cfc75b5f05d). This reduces the amount of boilerplate for socket file administration (-13 LoC), and avoids any synchronization due to its shared-nothing state. Is this okay with you?
> 
> Looks good!

@Michael-Mc-Mahon @jaikiran Thanks so much for the assistance! 🙇

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PR Comment: https://git.openjdk.org/jdk/pull/24126#issuecomment-2752326427