Experimental Physics and
Industrial Control System

Richard Pastrick <[email protected]> · Tue, 21 Oct 2008 15:25:48 -0700

I have some questions regarding EPICS and threading. Let me start by laying out the development environment.

I am developing an interface to an EPICS motor record using the CA API. I am using base 3.14.8.2. I am compiling under windows using Visual Studio 2008. I have successfully compiled all necessary components this way. I know that there are no issues with the compiling because all of the utilities and executables generated by the base are functional.

My interface is being generated in a GUI application for windows. When I start the program, the main process thread instantiates a class which contains all of my EPICS related code. This class will connect to the various PVs I require and store their chid objects for future access.

I then go on to do other necessary steps for my program and eventually I complete startup. Once startup has completed, there is a spawned thread which will go to my EPICS class at a specified interval and retrieve new data from the EPICS motors. These ca_get commands will fail to return any accurate data. The return code they return indicates a success but the data, as confirmed by both the caget utility and an MEDM window, is incorrect. For example, if I have moved the motor to a position of 2.5, both the MEDM window and caget will confirm that the RBV for that motor is 2.5. My program will say that it is at 0.

If I issue a ca_get right after I create the channels in the same thread that created the channels, I will receive the proper value of 2.5. I can also use ca_put with no problem. So if I issue a command to move to 4.2 from my program, the motor actually will move to this new location but the ca_get to retrieve the RBV will return 0 for the read value.

So my question boils down to this, should EPICS be able use a channel that was created in a different thread? 

Thank you,

Richard Pastrick
Associate Software Engineer
Xradia Inc
5052 Commercial Cir
Concord CA 94520
925-288-1228 Ext 1151
925-348-0384 (cell)

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System