Hi Yasumasa,
Yes that should work.
Can you please add assert where you removed the:
- MutexLocker mu(JvmtiThreadState_lock);
E.g.
+ // If we are in a handshake we only know that the requesting thread
should have locked it.
+ assert(SafepointSynchronize::is_at_safepoint() ||
JvmtiThreadState_lock->is_locked(), "Safepoint or must be locked");
Because I think you missing a MutexLocker in:
jvmtiExport.cpp line ~1650:
// remove the frame's entry
ets->clear_frame_pop(cur_frame_number);
In the method void JvmtiExport::post_method_exit(...).
Thanks, Robbin
On 2020-08-26 14:15, Yasumasa Suenaga wrote:
Hi Robbin,
Thanks for your comment!
How about this change?
webrev: http://cr.openjdk.java.net/~ysuenaga/JDK-8242427/webrev.01/
diff from previous webrev:
http://hg.openjdk.java.net/jdk/submit/rev/7facd1dd39d6
I still use JvmtiThreadState_lock because it has a different locking
range from SR lock.
Thanks,
Yasumasa
On 2020/08/26 18:13, Robbin Ehn wrote:
Hi Yasumasa,
You cannot take the MutexLocker mu(JvmtiThreadState_lock) with
safepoint checks inside a handshake.
We are missing a NoSafepointVerifier for handshakes.
(I have added this in my work in progress asynchronous handshake patch)
Also this can deadlock with the handshake semaphore.
(In my asynch handshake patch I have change the sema to a mutex, thus
lock ranking works.)
I solved this by just taking the mutex before the handshake.
And removed the internal locking from set_frame_pop, etc...
If there is an issue holding the JvmtiThreadState_lock to long, it
should split to a per thread lock instead.
(Since often the thread is suppose to be suspended, one could consider
using the SR lock for serializing access to the per thread
JvmtiThreadState instead.)
Thanks, Robbin
On 2020-08-26 09:34, Yasumasa Suenaga wrote:
Hi Patricio, David,
Thanks for your comment!
I updated webrev which includes the fix which is commented by
Patricio, and it passed submit repo. So I switch this mail thread to
RFR.
JBS: https://bugs.openjdk.java.net/browse/JDK-8242427
webrev: http://cr.openjdk.java.net/~ysuenaga/JDK-8242427/webrev.00/
I understand David said same concerns as Patricio about active
handshaker. This webrev checks active handshaker is current thread or
not.
Cheers,
Yasumasa
On 2020/08/26 10:13, Patricio Chilano wrote:
Hi Yasumasa,
On 8/23/20 11:40 PM, Yasumasa Suenaga wrote:
Hi all,
I want to hear your opinions about the change for JDK-8242427.
I'm trying to migrate following operations to direct handshake.
- VM_UpdateForPopTopFrame
- VM_SetFramePop
- VM_GetCurrentLocation
Some operations (VM_GetCurrentLocation and
EnterInterpOnlyModeClosure) might be called at safepoint, so I want
to use JavaThread::active_handshaker() in production VM to detect
the process is in direct handshake or not.
However this function is available in debug VM only, so I want to
hear the reason why it is for debug VM only, and there are no
problem to use it in production VM. Of course another solutions are
welcome.
I added the _active_handshaker field to the HandshakeState class
when working on 8230594 to adjust some asserts, where instead of
checking for the VMThread we needed to check for the active
handshaker of the target JavaThread. Since there were no other users
of it, there was no point in declaring it and having to write to it
for the release bits. There are no issues with having it in
production though so you could change that if necessary.
webrev is here. It passed jtreg tests
(vmTestbase/nsk/{jdi,jdwp,jvmti} serviceability/{jdwp,jvmti})
http://cr.openjdk.java.net/~ysuenaga/JDK-8242427/proposal/
Some comments on the proposed change.
src/hotspot/share/prims/jvmtiEnvThreadState.cpp,
src/hotspot/share/prims/jvmtiEventController.cpp
Why is the check to decide whether to call the handshake or execute
the operation with the current thread different for
GetCurrentLocationClosure vs EnterInterpOnlyModeClosure?
(GetCurrentLocationClosure)
if ((Thread::current() == _thread) || (_thread->active_handshaker()
!= NULL)) {
op.do_thread(_thread);
} else {
Handshake::execute_direct(&op, _thread);
}
vs
(EnterInterpOnlyModeClosure)
if (target->active_handshaker() != NULL) {
hs.do_thread(target);
} else {
Handshake::execute_direct(&hs, target);
}
If you change VM_SetFramePop to use handshakes then it seems you
could reach JvmtiEventControllerPrivate::enter_interp_only_mode()
with the current thread being the target.
Also I think you want the second expression of that check to be
(target->active_handshaker() == Thread::current()). So either you
are the target or the current active_handshaker for that target.
Otherwise active_handshaker() could be not NULL because there is
another JavaThread handshaking the same target. Unless you are
certain that it can never happen, so if active_handshaker() is not
NULL it is always the current thread, but even in that case this way
is safer.
src/hotspot/share/prims/jvmtiThreadState.cpp
The guarantee() statement exists in release builds too so the
"#ifdef ASSERT" directive should be removed, otherwise "current"
will not be declared.
Thanks!
Patricio
Thanks,
Yasumasa
