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| <== Date ==> | <== Thread ==> |
|---|
| Subject: | Re: subroutine, chaning links |
| From: | Tim Mooney <[email protected]> |
| To: | Ben Franksen <[email protected]> |
| Cc: | [email protected] |
| Date: | Fri, 30 May 2008 12:23:42 -0500 |
On Freitag, 30. Mai 2008, Mathias Steiner wrote:All would be well if it were possible to change links -- either .FLNK or .OUT -- from within a subroutine. I've tried a couple of things without success. Just pasting the channel name into the "value" field of the union does not, and probably should not, work.
Assigning a different value to a link by copying an input link doesn't work either: psub->flnk = psub->inpb;
This isn't so clear to me, since they are both of type DBLINK. After all, I can "just" type the value into the .FLNK field of any channel using edm, and it'll work...
It works because this operation is going via Channel Access.
You can do the same from your subroutine: use the CA client library to establish a channel to the FLNK (or whatever other link) field, then do a ca_put with the new value. A very simple example for how to use CA (client) is provides as a makeBaseApp template, just do
makeBaseApp.pl -t caClient
and look at caExample.c.
I am not sure whether the ca_context_create() call is necessary if you call CA from a subroutine record, maybe the context has already been initialized?
Cheers Ben
I think I would not do this from within a sub record's subroutine, even though it's possible. I would probably arrange for an SNL program, or for some string record's output link (with attribute 'CA'), to write to the links that need to be changed. A sub record's subroutine is not well positioned to perform as a CA client, and there seems to me little benefit to be gained, in the end, from coercing this. The subroutine can't use the new links until it returns and is re-entered (i.e., until the lock set has been released, and CA has had an opportunity to run), so you'll have the principal disadvantage of using an explicit third party, whether you actually use one or not.
-- Tim Mooney ([email protected]) (630)252-5417 Beamline Controls & Data Acquisition Group Advanced Photon Source, Argonne National Lab.