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