How to ensure with_ctrlvars monitor in PyEpics if PVs are initially unavailable

["Wang, Lin via Tech-talk" <tech-talk at aps.anl.gov>]

Dear all,

If the PV is ready, the following PyEpics code works normally and metadata is always available in callback,

import time, epics

def cb(**kw):

    print("units =", kw.get("units"))

pv = epics.PV("calcExample")

pv.wait_for_connection(timeout=5)

pv.add_callback(cb, with_ctrlvars=True)

time.sleep(10)

However, it seems that if the PV is not ready at first, the with_ctrlvars parameter will not take effect. In this case, even if the PV becomes accessible later, callback can never access metadata in subsequent updates.

So the questions: if PV metadata is intended to be available in callback no matter what status the PV is when calling add_callback(), is there any workaround? Or am I missing something?

Thanks,

Lin