Some clarification about JVMTI_EVENT_THREAD_START and PRIMORDIAL phase

[Jaroslav Bachorík]

Thank you all for chiming in!

My main concern was that the JDK 8 JVMTI spec
(https://docs.oracle.com/javase/8/docs/platform/jvmti/jvmti.html#ThreadStart)
was contradicting what was actually put to the EARLY_EVENT_BITS
variable and therefore which events were allowed in PRIMORDIAL and
ONLOAD (https://hg.openjdk.java.net/jdk8u/jdk8u-dev/hotspot/file/02b4fd2f9041/src/share/vm/prims/jvmtiEventController.cpp#l100)

So, if I went and remove `THREAD_START_BIT | THREAD_END_BIT` part from
the EARLY_EVENT_BITS in order to fix the assumed regression due to
JDK-8233197 I would be actually following the spec, right?

Cheers,

-JB-

On Mon, Jul 13, 2020 at 4:02 PM Daniel D. Daugherty
<daniel.daugherty at oracle.com> wrote:
>
> If there is going to be a spec change, then it would not affect JDK8.
> I don't think anyone has decided how this issue should be resolved yet.
>
> Dan
>
>
> On 7/13/20 7:10 AM, Sergey Nazarkin wrote:
> > Hi Daniel,
> >
> > Please correct me if I‘m wrong but the spec change will touch post-JDK8 releases only?
> >
> >
> >
> > Sergey Nazarkin
> >
> >
> >
> >
> >> On Jul 9, 2020, at 19:25, Daniel D. Daugherty <daniel.daugherty at oracle.com> wrote:
> >>
> >> On 7/9/20 9:07 AM, Jaroslav Bachorík wrote:
> >>> Hello,
> >>>
> >>> Recently, after backporting JDK-8233197 to JDK8u I received a report
> >>> from Sergey Nazarkin (cc) that the backport broke JVMTI spec basically
> >>> emitting JVMTI_EVENT_THREAD_START events in primordial phase while the
> >>> spec states that it should be emitted only in either start or live
> >>> phase.
> >>>
> >>> But if I am reading this correctly
> >>> (https://hg.openjdk.java.net/jdk8u/jdk8udev/hotspot/file/02b4fd2f9041/src/share/vm/prims/jvmtiEventController.cpp#l418)
> >>> the spec is also violated there.
> >>>
> >>> EARLY_EVENT_BITS are including THREAD_START_BIT and it is not filtered
> >>> out by THREAD_FILTERED_EVENT_BITS so it seems perfectly valid for
> >>> JVMTI_EVENT_THREAD_START to appear during PRIMORDIAL phase.
> >>>
> >>> So I would like to get clarification before going in and start
> >>> tinkering with the JVM initialization code order.
> >>>
> >>> Thanks!
> >>>
> >>> -JB-
> >> Hi Jaroslav!
> >>
> >> It has been a long time my friend... :-)
> >>
> >> It looks like that change was made by this Jigsaw change:
> >>
> >>      JDK-8072745 Re-examine JVM TI execution phases and expectations
> >>                  on what is allowed in each phase
> >>      https://bugs.openjdk.java.net/browse/JDK-8072745
> >>
> >> These diffs in the bug reported jumped out at me:
> >>
> >> @@ -1022,6 +1032,10 @@
> >>   void JvmtiExport::post_thread_start(JavaThread *thread) {
> >>     assert(thread->thread_state() == _thread_in_vm, "must be in vm state");
> >>
> >> + if (JvmtiEnv::get_phase() <= JVMTI_PHASE_PRIMORDIAL) {
> >> + return;
> >> + }
> >> +
> >>     EVT_TRIG_TRACE(JVMTI_EVENT_THREAD_START, ("JVMTI [%s] Trg Thread Start event triggered",
> >>                         JvmtiTrace::safe_get_thread_name(thread)));
> >>
> >> @@ -1050,6 +1064,10 @@
> >>
> >>
> >>   void JvmtiExport::post_thread_end(JavaThread *thread) {
> >> + if (JvmtiEnv::get_phase() <= JVMTI_PHASE_PRIMORDIAL) {
> >> + return;
> >> + }
> >> +
> >>     EVT_TRIG_TRACE(JVMTI_EVENT_THREAD_END, ("JVMTI [%s] Trg Thread End event triggered",
> >>                         JvmtiTrace::safe_get_thread_name(thread)));
> >>
> >>
> >> Here's the order of phases from jvmti.h:
> >>
> >>      /* Phases of execution */
> >>
> >> typedef enum {
> >>      JVMTI_PHASE_ONLOAD = 1,
> >>      JVMTI_PHASE_PRIMORDIAL = 2,
> >>      JVMTI_PHASE_START = 6,
> >>      JVMTI_PHASE_LIVE = 4,
> >>      JVMTI_PHASE_DEAD = 8
> >> } jvmtiPhase;
> >>
> >> However, the above diffs prevent the JVMTI_EVENT_THREAD_START
> >> and JVMTI_EVENT_THREAD_END events from being posted earlier than
> >> the JVMTI_PHASE_START phase... Unfortunately, I can't find the
> >> actual changeset pushed to the Jigsaw report for JDK-8072745.
> >>
> >>
> >> When you look at the current JvmtiExport::post_thread_start()
> >> and JvmtiExport::post_thread_end() functions, you can see this:
> >>
> >>      1: void JvmtiExport::post_thread_start(JavaThread *thread) {
> >> 36508:   if (JvmtiEnv::get_phase() < JVMTI_PHASE_PRIMORDIAL) {
> >> 36508:     return;
> >> 36508:   }
> >>
> >>      1: void JvmtiExport::post_thread_end(JavaThread *thread) {
> >> 36508:   if (JvmtiEnv::get_phase() < JVMTI_PHASE_PRIMORDIAL) {
> >> 36508:     return;
> >> 36508:   }
> >>
> >> $ hg log -r 36508
> >> changeset:   36508:5f9eee6b383b
> >> user:        alanb
> >> date:        Thu Mar 17 19:04:01 2016 +0000
> >> summary:     8142968: Module System implementation
> >>
> >>
> >> So the Jigsaw integration pushed a slightly different change
> >> than is shown in JDK-8072745. I don't know whether the fix
> >> for JDK-8072745 evolved before being pushed to the Jigsaw
> >> repos or whether another JBS issue was used to modify the
> >> code after JDK-8072745 was pushed.
> >>
> >> Short version: The semantics of the JVMTI_EVENT_THREAD_START
> >> and JVMTI_EVENT_THREAD_END were changed by Jigsaw, but the
> >> JVM/TI spec was not updated to reflect those changes.
> >>
> >> I've filed a new bug to track this issue:
> >>
> >>      JDK-8249158 THREAD_START and THREAD_END event posting changed
> >>                  by modules without updating the spec
> >>      https://bugs.openjdk.java.net/browse/JDK-8249158
> >>
> >> Dan
>