RFR: 8334215: serviceability/dcmd/thread/PrintMountedVirtualThread.java failing with JTREG_TEST_THREAD_FACTORY=Virtual

[Inigo Mediavilla Saiz]

On Mon, 17 Jun 2024 12:56:03 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> src/hotspot/share/runtime/threads.cpp line 1334:
>> 
>>> 1332:           if (p->is_vthread_mounted()) {
>>> 1333:             const oop vt = p->vthread();
>>> 1334:             if (vt != thread_oop) {
>> 
>> We need a comment explaining why we have to check for this as without knowing the implementation quirks it seems non-sensical for a thread to have mounted itself!
>
>> We need a comment explaining why we have to check for this as without knowing the implementation quirks it seems non-sensical for a thread to have mounted itself!
> 
> Just to note that JavaThread._vthread is always the "current thread". It's the virtual thread when mounted, the carrier (as in itself) when there is no virtual thread mounted. It's done this way so that the C2 instrinic for currentThread doesn't need a branch/test.

I wasn't aware of that, and I was going to suggest to add that information as documentation, but it seems to be already documented here: https://github.com/openjdk/jdk/blob/ad0b54d429fdbd806c09aa06bb42f1ed4a0297e8/src/hotspot/share/runtime/javaThread.hpp#L95

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PR Review Comment: https://git.openjdk.org/jdk/pull/19744#discussion_r1642798969