[jdk18] RFR: 8273107: RunThese24H times out with "java.lang.management.ThreadInfo.getLockName()" is null [v3]

[Daniel D.Daugherty]

On Fri, 17 Dec 2021 01:25:00 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

>> RunThese24H sometimes times out with a couple of error msgs:
>> - "java.lang.management.ThreadInfo.getLockName()" is null
>> - ForkJoin common pool thread stuck
>> 
>> The '"java.lang.management.ThreadInfo.getLockName()" is null' error msg was
>> due to RunThese's use of an older JCK test suite which has since been fixed.
>> 
>> The 'ForkJoin common pool thread stuck' failure mode is likely due to a thread
>> spending a lot of time in ObjectSynchronizer::monitors_iterate() due to a
>> VM_ThreadDump::doit() call. I say "likely" because I've never been able to
>> reproduce this failure mode in testing outside of Mach5. With the Mach5
>> sightings, all we have are thread dumps and core files and not a live process.
>> 
>> The VM_ThreadDump::doit() call is trying to gather owned monitor information
>> for all threads in the system. I've seen sightings of this failure mode with > 2000
>> threads. I've also seen passing runs with > 1.7 million monitors on the in-use list.
>> Imagine searching a larger in-use list for > 2000 threads. It just doesn't scale.
>
> Daniel D. Daugherty has updated the pull request incrementally with one additional commit since the last revision:
> 
>   coleenp CR - cleanup type safety

The `ObjectMonitor::_owner` field can contain a `JavaThread*`, the address of
a `BasicLock` on a JavaThread's stack, `nullptr` or `DEFLATER_MARKER` so the
`_owner` field is of type `void*`.

@coleenp pointed out off-line that I had a bit of type confusion in my new
`ObjectMonitorsHashtable`. Instead of indexing the Hashtable with a
`JavaThread*`, I should be indexing the Hashtable with a `void*` to reflect
the fact that my `_owner` field can be a `JavaThread*` or the address of a
`BasicLock` on the JavaThread's stack.

My most recent push to this PR cleans up the type confusion. This update
is tested with Mach5 Tier1 as a sanity check.

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

PR: https://git.openjdk.java.net/jdk18/pull/25