Jarsolav,
I'm copying this reply to the bug (JDK-8249158). I figure folks should
continue the conversation there.
Dan
On 7/14/20 9:31 AM, Jaroslav Bachorík wrote:
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
<[email protected]> 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 <[email protected]>
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
