Adding Serguei to this thread directly since he's back from vacation!
On 7/31/17 10:14 PM, David Holmes wrote:
Hi Dan,
On 26/07/2017 11:52 PM, Daniel D. Daugherty wrote:
On 7/26/17 12:11 AM, David Holmes wrote:
On 26/07/2017 10:27 AM, Yasumasa Suenaga wrote:
Hi Dan,
I've added some analysis to the bug report
Thanks!
I tried to fix this issue in JvmtiEnvBase::get_owned_monitors() at
first.
But it is difficult because we cannot know pending monitor if
thread state is MONITOR_CONTENDED_ENTER when get_owned_monitor() is
called.
I need to look closer at this when I get back from vacation next week.
Seems like you're back already. :-)
A pending monitor should not be reported as owned (unless the spec
says otherwise) and it seems odd to me to fix the current problem by
marking the monitor as pending earlier.
It's the updating of the _current_pending_monitor field that
allows JvmtiEnvBase::get_locked_objects_in_frame() to recognize
that the monitor observed in the frame is only pending and
is not owned.
I put a fairly detailed note in the bug yesterday, but you
should look at that when you're officially back!
Thanks for clarifying things. I also added a comment to the bug report.
I think the fix is sound and prevents anyone from observing the case
where the monitor will be seen in the stack-frame, but has not yet
been set as the "pending monitor". As far as I can tell it is only
this case (GetOwnedMonitorInfo from the contended-monitor event
callback in the current thread) that will be able to observe the change.
One scenario that I worry about here is that a GetCurrentContendedMonitor()
call on a target thread will now be able to return a non-NULL value for the
object, when GetThreadState() will be able to return something other than
blocked (on monitor enter) for the thread.
I don't see anything in the JVM/TI spec that says such a scenario is
wrong; I'm only worried about whether we have any tests that would catch
this slight change in behavior. In any case, one of these operations has
to "happen first":
- thread is marked as blocked
- monitor is flagged as contended
Currently, they happen in the above order and the fix proposes to
change the order and I see no reason not to do it.
I would like the test attached to the bug to be converted into a native
JTREG test that lives in hotspot/test/serviceability/jvmti. See the
following test as a possible example:
hotspot/test/serviceability/jvmti/GetNamedModule
for how to do this... I haven't done one of these new native JTREG
tests myself, but I believe Serguei has...
Dan
Thanks,
David
Dan
Thanks,
David
Did you run the jdk repo's com/sun/jdi tests with your fix?
I have not done yet.
I have a trip until 28 July JST. So I will run it after that.
Yasumasa
On 2017/07/26 7:05, Daniel D. Daugherty wrote:
On 7/24/17 8:40 PM, Yasumasa Suenaga wrote:
Hi all,
I tried to get owned monitors in MonitorContendedEnter JVMTI
event handler.
However GetOwnedMonitorInfo JVMTI function returns a monitor
which is
not yet owned.
I attached reproducer to JBS. Please read README.md.
I think GetOwnedMonitorInfo() should not return a pending monitor.
I uploaded webrev. Could you review?
http://cr.openjdk.java.net/~ysuenaga/JDK-8185164/webrev.00/
I hope this fix is applied to 8u or later release.
I cannot access JPRT. So I need a sponsor.
Thanks for the bug report. It's nice to have a test case and a
proposed
fix all in the bug report! I've added some analysis to the bug report
and we'll need to run this fix through Oracle's JPDA test stack which
is not (yet) open.
Did you run the jdk repo's com/sun/jdi tests with your fix?
Dan
Thanks,
Yasumasa
