RFR: 8253241: Update comment on java_suspend_self_with_safepoint_check()

[Richard Reingruber]

On Mon, 21 Sep 2020 04:12:39 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> After JDK-8252414 the safepoint/handshake code does not take _suspend_flags into accout anymore in its assessment if a
>> thread is safepoint/handshake safe. This change updates the comment on
>> JavaThread::java_suspend_self_with_safepoint_check().  I have (not yet) fixed the line breaks (fill-paragraph in emacs
>> lingo) for a clearer diff.
>> Also I could inline the (*) footnote.
>
> src/hotspot/share/runtime/thread.cpp line 2599:
> 
>> 2597: // safepoint/handshake code will count it as safepoint/handshake safe. Also it allows
>> 2598: // another thread to continue if it is waiting in is_ext_suspend_completed() for this
>> 2599: // thread to change state from _thread_in_native_trans to the target state.
> 
> The revised wording doesn't really convey the situation to me. We _have_ to set the thread-state to _thread_blocked so
> that a thread waiting in _is_ext_suspend_completed can proceed (there is no generic "target" state - it must be
> _thread_blocked). I would simplify and rephrase as follows:  "We have to set the thread state directly to
> _thread_blocked so that it will be seen to be safepoint/handshake safe whilst suspended. This is also necessary to
> allow a thread in is_ext_suspend_completed, that observed the _thread_in_native_trans state, to proceed."

Ok, I will use your version.

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

PR: https://git.openjdk.java.net/jdk/pull/225