Experimental Physics and
Industrial Control System

Weiwei Lu <[email protected]> · Tue, 23 Aug 2016 11:21:03 -0400 (EDT)

Hi Matt,

I will try to have our pyepics upgraded to the latest version.  For now, the solution you suggested that cache be cleared up after closing a channel should  work for me.

Thanks again for you help.
William

----- Original Message -----
From: "Matt Newville" <[email protected]>
To: "weiwei" <[email protected]>
Cc: "tech-talk" <[email protected]>
Sent: Tuesday, August 23, 2016 9:24:15 AM
Subject: Re: Is There A Way to Explicitly Close CA Connections in PyEpics?

Hi,

On Fri, Aug 19, 2016 at 10:50 AM, Weiwei Lu <[email protected]> wrote:

> Hi Matt,
>
> Many thanks for the suggestions.
>
> > What version of pyepics are you using?
>
> I think I am using pyepics-3.2.1, but not 100% sure.  Is there a command
> that can tell which version I am using?
>

You should be able to do
    import epics
    print(epics.__version__)

The latest version of pyepics is 3.2.6, and I'd suggest upgrading to the
latest version before trying to diagnose problems.

> Why do you want to do this?
>
> Well, just wanted to make the program more ioc friendly.  Closing the
> unused connections releases the resources (file descriptors, memory) of the
> iocs.  My program is a daemon program.  If it does not close the
> connections it has opened and are no longer needed, those connections will
> remain open forever.

Yes, that is true.

> Also how about the unresolved pv searches; will my program keeps searching
> those unresolved pvs forever if it does not close them explicitly?  So I
> think by closing the unused or unresolved pvs, these problems can be
> avoided.
>

The CA client library handles how often to search and connect to unresolved
PVs.  It seems like it's not often a problem to have a few unresolved
PVs.   But that's not to say that it is OK that you cannot fully disconnect
from PVs -- you should definitely be able to do that.

> >    import gc
> >    gc.collect()
>
> Calling gc.collect() after executing pv = None, the connection remained
> open.  So this does not work.
>

Hm, weird.  I don't know why that would be (especially given that the code
below works).  Upgrading to the latest version might help.

>
> >    epics.ca.clear_channel(chid)
> >    ctx =epics.ca.current_context()
> >    epics.ca._cache[ctx].pop(pvname)
>
> Yes, this works!  This clears the connection and also allows re-creation
> of a channel on the same pv.
>
>
--Matt

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System