Communication with another IOC

[jdmax]

I'm working on an application that will use several softiocs, and I'm try to figure out how to access the PVs from other IOCs.

I would typically just "import epics" and use "epics.caget('PV_name')". But I've found that in a script that imports from softioc, I get an error when trying to do this: "cannot connect to 'PV_name'." For instance, the following script will work, unless I uncomment the softioc imports. Any insight on how to get or put to other IOCs would be very much appreciated.

import epics
import asyncio
#from softioc import softioc, builder, asyncio_dispatcher

async def main():

    print(epics.caget('Test_PV'))

if __name__ == "__main__":
    asyncio.run(main())

[AlexanderWells-diamond]

I unfortunately don't know exactly what package you are referring to when you say import epics - there appears to be no package on PyPi of that exact name. I can say that the likely issue is regarding threading. The default softioc will start a cothread callback thread, and the main process must occasionally yield to allow cothread to run.

The way to solve this is to use either cothread or aioca depending on your preference for the async keyword - those documentation links should explain the differences.

[jdmax]

Thanks so much for your quick reply! The epics package I'm using is pyepics. I tried using cothread in the following example:

`import epics
import cothread
#from softioc import softioc, builder
import subprocess

def main():
cothread.Spawn(print(epics.caget('Test_PV')))

if name == "main":
main()`

Again, the print works immediately if I keep the softioc import commented, but if I uncomment it and run again, the program hangs as it waits for the epics get, then returns "cannot connect to Test_PV". Thanks again for your help.

[AlexanderWells-diamond]

I see the same issue when using your example and installing pyepics.

The issue is that pyepics and softioc have two different sources of EPICS code libraries. pyepics appears to use old, precompiled shared objects whereas pythonSoftIOC uses epicscorelibs. Trying to mix these two different sources of EPICS is effectively a non-starter - EPICS was never designed for this, and it causes problems all over the place.

You will need to use either cothread or aioca for the PV access inside pythonSoftIOC. I'd lean towards aioca as cothread has issues in Python3.11.

[jdmax]

Using aioca works well. I replaced the "epics.caget" with "await caget" and it is working as expected. Thanks again!