Experimental Physics and
Industrial Control System

pvapy 4.0.0 uses epics base 7.0.6, while 3.1.0 used 7.0.4.1. However, there were some changes in pvapy 4.0.0 related to support for asynchronous gets that might be causing this.

There were also changes to the caProvider inside pvAccess made between Base 7.0.4.1 and 7.0.5 that made it more strict about saving and restoring the CA context pointer for the current thread, and changed the thread which is used to perform notifications to the PVA client code. That could mean that calling pyepics code from inside a pvaccess callback/notification routine might no longer work if pyepics doesn’t properly set its CA context before calling routines inside libca (unfortunately that’s probably what’s happening, given the access violation that Mark is seeing).

Calling pvaccess routines from inside a pyepics callback should be safe because now the provider routines first save the thread’s current context, set their own context, call libca, and then restore the previous context before returning. However notifications from pvAccess may now be made by a thread that has no attached CA context, and if a libca routine gets called in that context it might trigger this kind of problem.

- Andrew