RFR: 8361103: java_lang_Thread::async_get_stack_trace does not properly protect JavaThread [v6]

[David Holmes]

On Wed, 30 Jul 2025 01:43:37 GMT, Alex Menkov <amenkov at openjdk.org> wrote:

>> The fix updates `java_lang_Thread::async_get_stack_trace()` (used by `java.lang.Thread.getStackTrace()` to get stack trace for platform and mounted virtual threads) to correctly use `ThreadListHandle` for thread protection.
>> 
>> Testing: tier1..5
>
> Alex Menkov has updated the pull request incrementally with one additional commit since the last revision:
> 
>   fix broken build

src/hotspot/share/classfile/javaClasses.cpp line 1885:

> 1883: }
> 1884: 
> 1885: oop java_lang_Thread::async_get_stack_trace(jobject jthread, TRAPS) {

Please add a comment describing how the method works for virtual threads, and what returning null implies.

src/hotspot/share/classfile/javaClasses.cpp line 1897:

> 1895:   class GetStackTraceHandshakeClosure : public HandshakeClosure {
> 1896:   public:
> 1897:     const Handle _thread_oop;

Thanks for making this change! Very confusing otherwise.

src/hotspot/share/classfile/javaClasses.cpp line 1939:

> 1937:           // Target thread has been unmounted.
> 1938:           return;
> 1939:         }

Shouldn't we set `carrier = true` if we don't return here? Or am I misunderstanding what "carrier" means here?

src/hotspot/share/classfile/javaClasses.cpp line 1941:

> 1939:       bool carrier = false;
> 1940:       if (java_lang_VirtualThread::is_instance(_java_thread())) {
> 1941:         // if (thread->vthread() != _java_thread()) // We might be inside a System.executeOnCarrierThread

Need to check with @AlanBateman whether this check is also needed (he does both in his draft PR).

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PR Review Comment: https://git.openjdk.org/jdk/pull/26119#discussion_r2253138892
PR Review Comment: https://git.openjdk.org/jdk/pull/26119#discussion_r2253140711
PR Review Comment: https://git.openjdk.org/jdk/pull/26119#discussion_r2253161591
PR Review Comment: https://git.openjdk.org/jdk/pull/26119#discussion_r2253160696