Some clarification about JVMTI_EVENT_THREAD_START and PRIMORDIAL phase
Sergey Nazarkin
snazarkin at azul.com
Mon Jul 13 11:10:35 UTC 2020
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
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