RFR: 8242427: JVMTI frame pop operations should use Thread-Local Handshakes

[Patricio Chilano]

Hi Yasumasa,

On 8/27/20 10:18 PM, Yasumasa Suenaga wrote:
> Hi Patricio,
>
> On 2020/08/27 15:20, Patricio Chilano wrote:
>> Hi Yasumasa,
>>
>> On 8/26/20 8:57 PM, Yasumasa Suenaga wrote:
>>> Hi Patricio,
>>>
>>> Thanks for your review, but webrev.00 has been rotten.
>>> Can you review webrev.02?
>>>
>>>   webrev: http://cr.openjdk.java.net/~ysuenaga/JDK-8242427/webrev.02/
>>>     diff between webrev.00 and webrev.01: 
>>> http://hg.openjdk.java.net/jdk/submit/rev/7facd1dd39d6
>>>     diff between webrev.01 and webrev.02: 
>>> http://hg.openjdk.java.net/jdk/submit/rev/2ef7feb5681f
>> Looks good to me. Can JvmtiEventController::set_frame_pop(), 
>> JvmtiEventController::clear_frame_pop() and 
>> JvmtiEventController::clear_to_frame_pop() still be called at a 
>> safepoint?
>
> No, and also I checked them with 
> assert(JvmtiThreadState_lock->is_locked()).
> webrev is here:
>
>   webrev: http://cr.openjdk.java.net/~ysuenaga/JDK-8242427/webrev.03/
>     diff from previous webrev: 
> http://hg.openjdk.java.net/jdk/submit/rev/2a2c02ada080
I see that you will change them with assert_lock_strong() as David 
suggested which I think is good.


Thanks,
Patricio
> Thanks,
>
> Yasumasa
>
>
>> Thanks,
>> Patricio
>>> Thanks,
>>>
>>> Yasumasa
>>>
>>>
>>> On 2020/08/27 7:50, Patricio Chilano wrote:
>>>> Hi Yasumasa,
>>>>
>>>> On 8/26/20 4:34 AM, 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/
>>>> The changes look good to me, thanks for fixing them.
>>>>
>>>> Patricio
>>>>> 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
>>>>>>
>>>>
>>