Summary

Specify minimal JVMTI PopFrame support for virtual threads.

Problem

The JVMTI PopFrame is allowed to be supported by implementations in a general form but no minimal support is defined by the spec.

Solution

Specify that the PopFrame can be used to pop current frame of a virtual thread suspended at an event.

Specification

The PopFrame thread parameter is described with only one statement:

The thread whose current frame is to be popped.

Extend it with:

The `PopFrame` function may be used to pop the current frame of a virtual
thread when it is suspended at an event. An implementation may support
popping the current frame of a suspended virtual thread in other cases.

The description of the JVMTI_ERROR_OPAQUE_FRAME error code is:

The thread is a virtual thread and the implementation is unable
to pop this frame.

Replace it with:

The thread is a suspended virtual thread and the implementation
was unable to pop the current frame.

The spec change is:

diff --git a/src/hotspot/share/prims/jvmti.xml b/src/hotspot/share/prims/jvmti.xml
index ae466071de2..d55db4f82ae 100644
--- a/src/hotspot/share/prims/jvmti.xml
+++ b/src/hotspot/share/prims/jvmti.xml
@@ -2958,6 +2958,10 @@ err = (*jvmti)->Deallocate(jvmti, stack_info);
           <jthread impl="noconvert"/>
             <description>
               The thread whose current frame is to be popped.
+              The <functionlink id="PopFrame"></functionlink> function may be used to
+              pop the current frame of a virtual thread when it is suspended at an event.
+              An implementation may support popping the current frame of a suspended
+              virtual thread in other cases.
             </description>
         </param>
       </parameters>
@@ -2967,8 +2971,8 @@ err = (*jvmti)-&gt;Deallocate(jvmti, stack_info);
           The implementation is unable to pop this frame.
         </error>
         <error id="JVMTI_ERROR_OPAQUE_FRAME">
-          The thread is a virtual thread and the implementation is unable
-          to pop this frame.
+          The thread is a suspended virtual thread and the implementation
+          was unable to pop the current frame.
         </error>
         <error id="JVMTI_ERROR_THREAD_NOT_SUSPENDED">
           Thread was not suspended and was not the current thread.