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

[Kevin Walls]

On Wed, 25 Jun 2025 23:50:59 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> 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.

Yes thanks Dan! Will update.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25958#discussion_r2168498780