RFR: 8247972: incorrect implementation of JVM TI GetObjectMonitorUsage [v4]

[Daniel D. Daugherty]

On Tue, 13 Feb 2024 08:39:38 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

>> Sorry really struggling to understand this now. We have gone from a simple miscalculation to apparently doing everything wrong.
>> 
>> IIUC this API does not currently handle virtual threads correctly -i s that the case? If so I would like to see that fix factored out and done separately before this fix is done. Thanks.
>
>> Sorry really struggling to understand this now. We have gone from a simple miscalculation to apparently doing everything wrong. IIUC this API does not currently handle virtual threads correctly - is that the case? If so I would like to see that fix factored out and done separately before this fix is done. Thanks.
> 
> Thank you for the concern, David. But it is not clear what it is. Could you, please, explain a little bit?
> Why do you think the virtual threads are handled incorrectly?

@sspitsyn - When you get the chance, can you checkout these possible
changes for the objmonusage001 test?

https://github.com/openjdk/jdk/pull/17839

Summary of my test changes:
- extend the check() function to verify more of the jvmtiMonitorUsage fields
- add detailed comments at each of the verification points so it's clear what is being verified and why
- add a better summary for the overall test
- make it clear which output lines document failures

I've also made some temporary debugging changes that are only useful
while updating this test:
- temporarily use the "printdump" parameter to enable test output
- add a flag to verify the current JVMs bad jvmtiMonitorUsage fields so that the test can pass with an unmodified JVM
- add a flag to add a delay that helps check for a lack of races in the verification points

These proposed test changes help document how I think the GetObjectMonitorUsage API
is supposed to work on a simple test case.

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PR Comment: https://git.openjdk.org/jdk/pull/17680#issuecomment-1942747157