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

[Daniel D. Daugherty]

On Wed, 25 Jun 2025 13:02:03 GMT, Kevin Walls <kevinw at openjdk.org> wrote:

>> ThreadDumper/ThreadSnapshot need to handle a failure to resolve the native VM JavaThread from a java.lang.Thread.  This is hard to reproduce but a thread that has since terminated can provoke a crash.  Recognise this and return a null ThreadSnapshot.
>
> Kevin Walls has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - comment update
>  - comment update

Changes requested by dcubed (Reviewer).

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*`.

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

PR Review: https://git.openjdk.org/jdk/pull/25958#pullrequestreview-2959809320
PR Review Comment: https://git.openjdk.org/jdk/pull/25958#discussion_r2167723492