RFR: 8346792: serviceability/jvmti/vthread/GetThreadState/GetThreadState.java testObjectWaitMillis failed [v11]

[David Holmes]

On Mon, 27 Jan 2025 09:31:22 GMT, Serguei Spitsyn <sspitsyn at openjdk.org> wrote:

>> Below is the root cause of the bug described by Patricio:
>> The root of the issue is similar to [JDK-8345543](https://bugs.openjdk.org/browse/JDK-8345543), but instead of `JavaThreadBlockedOnMonitorEnterState`, the interaction here is with its equivalent for Object.wait, `JavaThreadInObjectWaitState`.
>> 
>> We change the `Thread.State` of the carrier to `TIMED_WAITING` before we try preempting the `vthread`. So we can see the `Thread.State` of the vthread as `TIMED_WAITING` before even calling `try_preempt()` (when the state is `RUNNING` we return the `Thread.State` of the carrier). Then when we check for `JVMTI_THREAD_STATE_BLOCKED_ON_MONITOR_ENTER`, we caught the `vthread` in `afterYield()` still with the transitional state of `TIMED_WAITING`, which is mapped to `Thread.State.RUNNABLE`.
>> 
>> The fix is to delay the state change to `JavaThreadStatus::IN_OBJECT_WAIT*` the point after block with the `try_preempt()` call. The fix is not elegant and hacky but I do not see a better solution. The ugliness comes from the fact that the `ObjectMonitor::wait()` is called from two places: `ObjectSynchronizer::wait()` and `ObjectSynchronizer::waitUninterruptibly()`. We do not need the `JavaThreadInObjectWaitState` in the second cases, so the object is defined in the `JVM_MonitorWait()` but not in the `ObjectMonitor::wait()`.
>> Maybe, deep refactoring the`JavaThreadInObjectWaitState` base class `JavaThreadStatusChanger` could be a better solution but it is going to be much more intrusive.
>> 
>> Testing:
>>  - Checked the failed test does not fail with the fix: `serviceability/jvmti/vthread/GetThreadState/GetThreadState.java`
>>  - Ran mach5 tiers 1-6
>
> Serguei Spitsyn has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review: refactor - get rid of ObjectMonitor::post_monitor_wait

Changes requested by dholmes (Reviewer).

src/hotspot/share/runtime/objectMonitor.cpp line 1653:

> 1651: }
> 1652: 
> 1653: 

Spurious newline?

src/hotspot/share/services/threadService.hpp line 493:

> 491:     JavaThreadStatusChanger(java_thread,
> 492:                             interruptible ? (timed ? JavaThreadStatus::IN_OBJECT_WAIT_TIMED : JavaThreadStatus::IN_OBJECT_WAIT)
> 493:                                           : java_lang_Thread::get_thread_status(java_thread->threadObj())) {

I think we need some explanatory comments here. It took me a while to understand how interruptible==false caused this to all be a (very inefficient) no-op. Thanks

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PR Review: https://git.openjdk.org/jdk/pull/23126#pullrequestreview-2582907568
PR Review Comment: https://git.openjdk.org/jdk/pull/23126#discussion_r1935001556
PR Review Comment: https://git.openjdk.org/jdk/pull/23126#discussion_r1935007640