RFR: 8364343: ThreadSnapshotFactory::get_thread_snapshot() crashes without JVMTI agent [v2]

[Patricio Chilano Mateo]

On Wed, 19 Nov 2025 13:50:44 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> Patricio Chilano Mateo has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Add fixes to DumpThreadsWithEliminatedLock.java
>
> src/java.base/share/classes/java/lang/VirtualThread.java line 1390:
> 
>> 1388:     }
>> 1389: 
>> 1390:     // -- JVM TI support --
> 
> We'll need to update is comment as it no longer only for JVMTI. 
> 
> This might be a good place for a block comment to define "transitions" covering the changing of thread identity the continuation mount/unmount, and how the notification to the VM support JVMTI and handshakes.  Maybe I could contribute a block comment to include here?

That would be great.

> src/java.base/share/native/libjava/VirtualThread.c line 38:
> 
>> 36:     { "startFinalTransition",     "()V",  (void *)&JVM_VirtualThreadEnd },
>> 37:     { "startTransition",          "(Z)V", (void *)&JVM_VirtualThreadStartTransition },
>> 38:     { "endTransition",            "(Z)V", (void *)&JVM_VirtualThreadEndTransition },
> 
> I wonder if JVM_VirtualThreadStart and JVM_VirtualThreadEnd should be renamed to have EndFirstTransition and StartFinalTransaction in the names so it's easy to follow through from the Java code down to MountUnmountDisabler::start_transition/end_transition.

How about removing these methods and just have an extra boolean parameter in `start/endTransition`?
https://github.com/pchilano/jdk/compare/JDK-8364343...pchilano:jdk:startEndTransitionsOnly

> test/jdk/com/sun/management/HotSpotDiagnosticMXBean/DumpThreadsWhenParking.java line 94:
> 
>> 92:                 });
>> 93:             }
>> 94:             // wait for all virtual threads to start so all have a non-empty stack
> 
> This reminds me the loom repo has a small update to to the DumpThreadsWithEliminatedLock.java test to ensure that the virtual thread starts execution before doing the thread dump. This was noticed with test-repeat runs of the new test to ensure it was stable.

Added the fixes to `DumpThreadsWithEliminatedLock.java` from the loom repo.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28361#discussion_r2543217770
PR Review Comment: https://git.openjdk.org/jdk/pull/28361#discussion_r2543212884
PR Review Comment: https://git.openjdk.org/jdk/pull/28361#discussion_r2543215701