Re: RFR: 8248362: JVMTI frame operations should use Thread-Local Handshake

[Daniel D. Daugherty]

On 7/22/20 11:12 PM, Yasumasa Suenaga wrote:

Hi Dan,

Thanks for your comment!
I uploaded new webrev:

  http://cr.openjdk.java.net/~ysuenaga/JDK-8248362/webrev.01/

  Diff from previous webrev: http://hg.openjdk.java.net/jdk/submit/rev/df75038b5449

Thumbs up. Reviewed by comparing the previous webrev patch (webrev.00) with
the latest (webrev.01).

Dan

On 2020/07/23 10:04, Daniel D. Daugherty wrote:

On 7/22/20 10:38 AM, Yasumasa Suenaga wrote:

Hi all,

Please review this change:

  JBS: https://bugs.openjdk.java.net/browse/JDK-8248362
  webrev: http://cr.openjdk.java.net/~ysuenaga/JDK-8248362/webrev.00/

src/hotspot/share/prims/jvmtiEnv.cpp
     L1755     // JVMTI get java stack frame location at safepoint.
         You missed updating this one. Perhaps:

               // JVMTI get java stack frame location via direct handshake.

Fixed.

src/hotspot/share/prims/jvmtiEnvBase.cpp
     L1563:   JavaThread* jt = _state->get_thread();
     L1564:   assert(target == jt, "just checking");

         This code is different than the other closures. It might be worth          a comment to explain why. I don't remember why VM_GetFrameCount had          to use the JvmtiThreadState to fetch the JavaThread. Serguei might

         remember.

         It could be that we don't need the _state field anymore because of          the way that handshakes work (and provide the JavaThread* to the          do_thread() function). Your choice on whether to deal with that as

         part of this fix or following with another RFE.

         Update: Uggg.... the get_frame_count() function takes JvmtiThreadState          as a parameter. This is very much entangled... sigh... we should

         definitely look at untangling this in another RFE...

I want to fix it in another RFE as you said if it is needed.
If we don't hear the reason from Serguei, I want to keep this change.

     old L1565:   ThreadsListHandle tlh;
     new L1565:   if (!jt->is_exiting() && jt->threadObj() != NULL) {

         Please consider add this comment above L1565:

                  // ThreadsListHandle is not needed due to direct handshake.

         Yes, I see that previous closures were added without that comment,          but when I see "if (!jt->is_exiting() && jt->threadObj() != NULL)"          I immediately wonder where the ThreadsListHandle is... Please consider

         adding the comment to the others also.

     old L1574:   ThreadsListHandle tlh;
     new L1574:   if (!jt->is_exiting() && jt->threadObj() != NULL) {

         Please consider add this comment above L1574:

                  // ThreadsListHandle is not needed due to direct handshake.

I think it is new normal as David said in the reply, and also other closures don't say about it.

So I did not change about it in new webrev.

src/hotspot/share/prims/jvmtiEnvBase.hpp
     L580: // HandshakeClosure to frame location.
         typo - s/to frame/to get frame/

Fixed.

src/hotspot/share/prims/jvmtiThreadState.cpp
     No comments on the changes.

     For the above comments about VM_GetFrameCount, understanding why
     JvmtiThreadState::count_frames() has to exist in JvmtiThreadState
     will go along way towards untangling the mess.

src/hotspot/share/runtime/vmOperations.hpp
     No comments.


Thumbs up. I only have nits above. If you choose to make the above
changes, I do not need to see another webrev.

Thanks, but I uploaded new webrev just in case :)


Yasumasa

Dan

Migrate JVMTI frame operations to Thread-Local Handshakes from VM Operations.

    - VM_GetFrameCount
    - VM_GetFrameLocation

They affects both GetFrameCount() and GetFrameLocation() JVMTI functions.

This change has passed all tests on submit repo (mach5-one-ysuenaga-JDK-8248362-20200722-1249-12859056), and vmTestbase/nsk/{jdi,jdw,jvmti}, serviceability/{jdwp,jvmti} .

Thanks,

Yasumasa