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

[David Holmes]

Hi Yasumasa,

On 23/07/2020 12:38 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/

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

     - VM_GetFrameCount
     - VM_GetFrameLocation

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

Your changes all seem fine.

But I'm a bit confused about the existing code. In 
JvmtiEnv::GetFrameLocation we have:

   if (java_thread == JavaThread::current()) {
     err = get_frame_location(java_thread, depth, method_ptr, 
location_ptr);

but then in get_frame_location we have:

   assert((SafepointSynchronize::is_at_safepoint() ||
           java_thread->is_thread_fully_suspended(false, &debug_bits)),
           "at safepoint or target thread is suspended");

and that assert must surely fire if called by the current thread for 
itself! ???

Thanks,
David

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