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

[Yasumasa Suenaga]

Hi Richard,

I've described the motivation on JDK-8201641 (it is a parent task of JDK-8242427)

```
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.
```

I aimed to improve JVMTI monitor operation with TLS at first, but I found other JVMTI operations can be improved with same process. So I've tried to fix them.

I proposed it to serviceability-dev [1], then Dan told me similar enhancement is already filed to JBS [2]. So I created subtasks in it.


Thanks,

Yasumasa


[1] https://mail.openjdk.java.net/pipermail/serviceability-dev/2020-March/030890.html
[2] https://mail.openjdk.java.net/pipermail/serviceability-dev/2020-March/030897.html


On 2020/08/27 5:33, Reingruber, Richard wrote:
> Hi Yasumasa,
> 
> Could you explain a little bit the motivation to replace these vm operations with handshakes?
> Would be good, if you could add the goals as well to the JBS item.
> 
> Thanks, Richard.
> 
> -----Original Message-----
> From: serviceability-dev <serviceability-dev-retn at openjdk.java.net> On Behalf Of Yasumasa Suenaga
> Sent: Montag, 24. August 2020 04:40
> To: serviceability-dev <serviceability-dev at openjdk.java.net>
> Subject: 8242427: JVMTI frame pop operations should use Thread-Local Handshakes
> 
> 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.
> 
> webrev is here. It passed jtreg tests (vmTestbase/nsk/{jdi,jdwp,jvmti} serviceability/{jdwp,jvmti})
>     http://cr.openjdk.java.net/~ysuenaga/JDK-8242427/proposal/
> 
> 
> Thanks,
> 
> Yasumasa
>