Hi, adding the same comment as in the bug regarding
GetThreadListStackTraces.
Please note that there is a semantic difference taking samples in a
safepoint and in handshakes, if there are mutiple thread sampled.
With a safepoint; stacktraces are taken from the same exact moment (from
a Java mutation perspective).
But with handshake we can have mutation between the samples, consider:
Thread A enters a mutual exclusive region, and get sampled inside that
region.
Thread A leaves the mutual exclusive region.
Thread B enter the same mutual exclusive region, and get sampled inside
that region.
When looking at the stack-traces, we have have two thread inside the
same mutual exclusive region.
If you are not aware on how the sampling mechanism works, this could be
confusing.
Please verify that we are still following JVM TI specs and at least have
information about this change in release notes.
Thanks, Robbin
On 2020-03-31 16:41, Daniel D. Daugherty wrote:
Add Robbin to this thread...
This reminded of the following RFE that Robbin filed:
JDK-8201641 JVMTI: GetThreadListStackTraces should use Thread-Local
Handshakes
https://bugs.openjdk.java.net/browse/JDK-8201641
We could update 8201641 to include everything that Yasumasa-san is
requesting.
Would be a good place to track it...
Dan
On 3/31/20 7:40 AM, Yasumasa Suenaga wrote:
Hi David,
On 2020/03/31 19:16, David Holmes wrote:
Hi Yasumasa,
On 31/03/2020 8:06 pm, Yasumasa Suenaga wrote:
Hi all,
Many JVMTI functions uses VM Operation to get information. However
some of them need to stop only one thread - they don't need to stop
all threads.
So I think we can use Thread Local Handshake as this webrev. It is
example for GetOneCurrentContendedMonitor().
True, but at the moment handshakes involve the VMThread. There is
work being done to support direct thread-to-thread handshakes and
once that is done this kind of conversion should be more easily done.
It might be worth waiting for that.
Thanks, I will be back to this topic when thread-to-thread handshake
is done.
I wondered at first why VMThread involves handshake. Its improvement
is welcome for me ;)
Cheers,
Yasumasa
http://cr.openjdk.java.net/~ysuenaga/jvmti-thread-local-handshake/
An observation, it seems to me that calling_thread is not used when
this is not a VMOperation.
Cheers,
David
Also I think we can replace following VM Operations to Thread Local
Handshake:
class VM_GetCurrentLocation
class VM_EnterInterpOnlyMode
class VM_UpdateForPopTopFrame
class VM_SetFramePop
class VM_GetOwnedMonitorInfo
class VM_GetCurrentContendedMonitor
class VM_GetFrameCount
class VM_GetFrameLocation
What do you think?
It it is acceptable, I will file it to JBS and send review request.
Thanks,
Yasumasa
