RFR: 8353718: Improve droppingMessage test in async UL tests

[Johan Sjölen]

On Thu, 3 Apr 2025 10:35:29 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

> Hi,
> 
> The test for dropping messages have started to fail on aarch64 fast debug on Linux only. It's currently unclear why this occurs. To figure out why, I've extended the test to do emit more diagnostic information if it fails.
> 
> 1. Fail if the asynchronous mode isn't "drop" (the test makes no sense with stalling mode)
> 2. Print the entirety of the log file produced if no missing messages are found
> 3. If the thread running the test is unattached, then async UL will emit log messages in synchronous mode. Therefore, if the thread is unattached, the test now fails with an error message.
> 
> With these changes integrated, I hope to be able to find the actual culprit of this bug.
> 
> I have attempted to reproduce this bug on both mainline and with this patch, but I have been unable to do so.

I managed to replicate the error by running the entire test group that this particular test was a part of. The current issue is truly in the log file, it's printed as a string of `?` for the most part.

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PR Comment: https://git.openjdk.org/jdk/pull/24411#issuecomment-2778778415