Hello,
I'd like to propose a new revision of the JVMTI spec, 1.2.1 to be
implemented by Hotspot in JDK 7, with the addition of a new method,
GetThisObject() (defined below). This new function would be part of
the 'Local Variable" set of functions. The motivation for this
addition is better filtering of JDI events in the situations where
events are raised in the context of a native method. This function
would use a new slot in the function pointer table, so the 1.2 version
of JVMTI will be backward-compatible with version 1.1. Clients using
JVMTI 1.1 or 1.0 would be unaffected by this change, other than
observing that GetVersion() function returns the new revision number.
Comments? Suggestions? Complaints?
Get This Object
jvmtiError
GetThisObject(jvmtiEnv* env,
jthread thread,
jint depth,
jobject* value_ptr)
This function can be used to retrieve the value of the local object
variable at slot 0 (the "this" object) from non-static frames. This
function can retrieve the "this" object from native activations,
whereas GetLocalObject() would return JVMTI_ERROR_OPAQUE_FRAME for
those frames.
Phase Callback Safe Position Since
may only be called during the live phase No 155 1.2
Capabilities
Optional Functionality: might not be implemented for all virtual
machines. The following capability (as returned by GetCapabilities)
must be true to use this function.
Capability Effect
can_access_local_variables Can set and get local variables
Parameters
Name Type Description
thread jthread The thread of the frame containing the variable's
value. If thread is NULL, the current thread is used.
depth jint The depth of the frame containing the variable's value.
value_ptr jobject* On return, points to the variable's value.
Agent passes a pointer to a jobject. On return, the jobject has been
set. The object returned by value_ptr is a JNI local reference and
must be managed.
Errors
This function returns either a universal error or one of the following
errors
Error Description
JVMTI_ERROR_MUST_POSSESS_CAPABILITY The environment does not possess
the capability can_access_local_variables. Use AddCapabilities.
JVMTI_ERROR_INVALID_SLOT If the activation corresponds to a static
method.
JVMTI_ERROR_INVALID_THREAD thread is not a thread object.
JVMTI_ERROR_THREAD_NOT_ALIVE thread is not live (has not been started
or is now dead).
JVMTI_ERROR_ILLEGAL_ARGUMENT depth is less than zero.
JVMTI_ERROR_NO_MORE_FRAMES There are no stack frames at the specified
depth.
JVMTI_ERROR_NULL_POINTER value_ptr is NULL.
