RFR: 8359870: JVM crashes in AccessInternal::PostRuntimeDispatch [v5]

[David Holmes]

On Wed, 25 Jun 2025 22:08:17 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

>> Kevin Walls has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - comment update
>>  - comment update
>
> src/hotspot/share/services/threadService.cpp line 1477:
> 
>> 1475:     java_thread = java_lang_Thread::thread(thread_h());
>> 1476:     if (java_thread == nullptr) {
>> 1477:         return nullptr; // thread terminated
> 
> This is not the right way to determine if you have a valid JavaThread
> when you have created a ThreadsListHandle. This code near the top
> of `ThreadSnapshotFactory::get_thread_snapshot` is not right:
> 
> 
>   ThreadsListHandle tlh(THREAD);
>   ResourceMark rm(THREAD);
>   HandleMark   hm(THREAD);
>   Handle thread_h(THREAD, JNIHandles::resolve(jthread));
> 
> 
> The above code was added by:
> [JDK-8357650](https://bugs.openjdk.org/browse/JDK-8357650) ThreadSnapshot to take snapshot of thread for thread dumps
> 
> Here's the example code from src/hotspot/share/runtime/threadSMR.hpp:
> 
> // JNI jobject example:
> //   jobject jthread = ...;
> //   :
> //   ThreadsListHandle tlh;
> //   JavaThread* jt = nullptr;
> //   bool is_alive = tlh.cv_internal_thread_to_JavaThread(jthread, &jt, nullptr);
> //   if (is_alive) {
> //     :  // do stuff with 'jt'...
> //   }
> 
> 
> So instead of this line:
> 
> Handle thread_h(THREAD, JNIHandles::resolve(jthread));
> 
> which does not guarantee you a valid JavaThread handle, you should
> use `tlh.cv_internal_thread_to_JavaThread` to get a `JavaThread*`.

Great catch Dan! I totally missed the TLH at the start of `get_thread_snapshot`. I knew something was off here but couldn't quite put my finger on it.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25958#discussion_r2167822932