Summary

Specify minimal JVMTI ForceEarlyReturn support for virtual threads.

Problem

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

Solution

Specify that the ForceEarlyReturnXXX functions can be used to force early return from the current frame of a virtual thread suspended at an event.

Specification

The ForceEarlyReturn description starts with the statement:

These functions allow an agent to force a method
to return at any point during its execution.

Replace it with:

These functions allow an agent to force a return from the current frame.
The specified thread must be suspended or must be the current thread.
These functions may be used to force a return from the current frame
of a virtual thread when it is suspended at an event.
An implementation may support forcing a return from the current frame
of a suspended virtual thread in other cases.

Remove the duplication of the line which was already copied to the beginning of description (see above):

The specified thread must be suspended or must be the current thread.

The description of the JVMTI_ERROR_OPAQUE_FRAME error code for each ForceEarlyReturnXXX function is:

The thread is a virtual thread and the implementation is
unable to force its current frame to return.

Replace it with:

The thread is a suspended virtual thread and the implementation was
unable to force its current frame to return.

The spec change is:

diff --git a/src/hotspot/share/prims/jvmti.xml b/src/hotspot/share/prims/jvmti.xml
index ae466071de2..2f6ac9e5d1c 100644
--- a/src/hotspot/share/prims/jvmti.xml
+++ b/src/hotspot/share/prims/jvmti.xml
@@ -3067,8 +3067,12 @@ err = (*jvmti)->Deallocate(jvmti, stack_info);

   <category id="ForceEarlyReturn" label="Force Early Return">
     <intro>
-      These functions allow an agent to force a method
-      to return at any point during its execution.
+      These functions allow an agent to force a return from the current frame.
+      The specified thread must be suspended or must be the current thread.
+      These functions may be used to force a return from the current frame
+      of a virtual thread when it is suspended at an event.
+      An implementation may support forcing a return from the current frame
+      of a suspended virtual thread in other cases.
       The method which will return early is referred to as the <i>called method</i>.
       The called method is the current method
       (as defined by
@@ -3076,7 +3080,6 @@ err = (*jvmti)-&gt;Deallocate(jvmti, stack_info);
       for the specified thread at
       the time the function is called.
       <p/>
-      The specified thread must be suspended or must be the current thread.
       The return occurs when execution of Java programming
       language code is resumed on this thread.
       Between calling one of these functions and resumption
@@ -3132,7 +3135,7 @@ err = (*jvmti)-&gt;Deallocate(jvmti, stack_info);
         <error id="JVMTI_ERROR_OPAQUE_FRAME">
           Attempted to return early from a frame
           corresponding to a native method.
-          The thread is a virtual thread and the implementation is
+          The thread is a suspended virtual thread and the implementation was
           unable to force its current frame to return.
           Or the implementation is unable to provide
           this functionality on this frame.
@@ -3184,7 +3187,7 @@ err = (*jvmti)-&gt;Deallocate(jvmti, stack_info);
         <error id="JVMTI_ERROR_OPAQUE_FRAME">
           Attempted to return early from a frame
           corresponding to a native method.
-          The thread is a virtual thread and the implementation is
+          The thread is a suspended virtual thread and the implementation was
           unable to force its current frame to return.
           Or the implementation is unable to provide
           this functionality on this frame.
@@ -3232,7 +3235,7 @@ err = (*jvmti)-&gt;Deallocate(jvmti, stack_info);
         <error id="JVMTI_ERROR_OPAQUE_FRAME">
           Attempted to return early from a frame
           corresponding to a native method.
-          The thread is a virtual thread and the implementation is
+          The thread is a suspended virtual thread and the implementation was
           unable to force its current frame to return.
           Or the implementation is unable to provide
           this functionality on this frame.
@@ -3277,7 +3280,7 @@ err = (*jvmti)-&gt;Deallocate(jvmti, stack_info);
         <error id="JVMTI_ERROR_OPAQUE_FRAME">
           Attempted to return early from a frame
           corresponding to a native method.
-          The thread is a virtual thread and the implementation is
+          The thread is a suspended virtual thread and the implementation was
           unable to force its current frame to return.
           Or the implementation is unable to provide
           this functionality on this frame.
@@ -3322,7 +3325,7 @@ err = (*jvmti)-&gt;Deallocate(jvmti, stack_info);
         <error id="JVMTI_ERROR_OPAQUE_FRAME">
           Attempted to return early from a frame
           corresponding to a native method.
-          The thread is a virtual thread and the implementation is
+          The thread is a suspended virtual thread and the implementation was
           unable to force its current frame to return.
           Or the implementation is unable to provide
           this functionality on this frame.
@@ -3361,7 +3364,7 @@ err = (*jvmti)-&gt;Deallocate(jvmti, stack_info);
         <error id="JVMTI_ERROR_OPAQUE_FRAME">
           Attempted to return early from a frame
           corresponding to a native method.
-          The thread is a virtual thread and the implementation is
+          The thread is a suspended virtual thread and the implementation was
           unable to force its current frame to return.
           Or the implementation is unable to provide
           this functionality on this frame.