RFR: 8338934: vmTestbase/nsk/jvmti/*Field*Watch/TestDescription.java tests timeout intermittently

[Serguei Spitsyn]

On Thu, 29 Aug 2024 18:18:12 GMT, Leonid Mesnik <lmesnik at openjdk.org> wrote:

> The tests time out because of dedlock of  of the thread that is in transition and thread changing field watches. 
> 
> They use JvmtiThreadState_lock and JvmtiVTMSTransitionDisabler.
> 
> The change field watch require disabler, but attempt to use it only when already locked in 
> 
> void
> JvmtiEventController::change_field_watch(jvmtiEvent event_type, bool added) {
>   MutexLocker mu(JvmtiThreadState_lock);
>   JvmtiEventControllerPrivate::change_field_watch(event_type, added);
> }
> 
> 
> while it is needed to first disable transitions and then try to use JvmtiThreadState_lock.
> I quickly looked that most of jvmti methods do it already. Also moved disabler into jvmtiEmv.cpp to be more consistent with other methods.
> 
> 
> I was able to verify my fix in loom repo locally. and run tier1 + tier5-svc testing in jdk.

Looks good.
Thank you for jumping to this.
The fix is as I initially wanted to have.

src/hotspot/share/runtime/mutexLocker.cpp line 270:

> 268:   MUTEX_DEFN(DirectivesStack_lock            , PaddedMutex  , nosafepoint);
> 269: 
> 270:   MUTEX_DEFN(JvmtiVTMSTransition_lock        , PaddedMonitor, safepoint); // used for Virtual Thread Mount State transition management

Nit: It'd better to align the comment at the end.

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

PR Review: https://git.openjdk.org/jdk/pull/20776#pullrequestreview-2269901775
PR Review Comment: https://git.openjdk.org/jdk/pull/20776#discussion_r1736969973