Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Tue, 29 Mar 2011 10:32:54 -0500

Hi Dirk,

On Tuesday 29 March 2011 09:45:08 Dirk Zimoch wrote:
> Unfortunately this behavior bites me now. After upgrading to a new OS
> and thus Tcl/Tk version, it turned out that monitors in our EPICS-Tcl
> interface did not work any more. This is because Tcl now can be compiled
> "thread aware" (which has been done by the distributor) and refuses to
> accept commands that come from a different thread.

Do you maintain your own Tcl interface to CA?  I know that we still use Tcl/Tk 
quite a lot here at APS — maybe if you were to post a question about CA and 
Tcl rather than the CA internals you might get a more useful and positive 
answer.  I suspect that this problem might have already been solved, or there 
will at least be other people interested in helping to solve it (collaboration 
is almost always better than forking).

There are probably other ways to fix this too, you may be able to register the 
callback thread with Tcl to allow yourself to run the command in that same 
thread.  However I'm pretty sure that CA runs callbacks from a separate thread 
for each CA server, so you can't just register one thread, you have to be 
prepared to do it lots of times.  You may need to register and use an 
epicsThreadPrivate variable to store any thread-specific data, and use 
epicsAtThreadExit() to clean up when CA is closing down.

HTH,

- Andrew
-- 
An error is only a mistake if you don't learn from it.
When you learn something from it, it becomes a lesson.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System