Experimental Physics and
Industrial Control System

Ben Franksen <[email protected]> · Tue, 26 Oct 2010 22:17:36 +0200

I am again hacking on the sequencer internals and thereby came to ask 
myself how CA handles these cases:

- multiple ca_put_callback calls on the same channel
- multiple ca_get_callback calls on the same channel
- multiple (blocking) ca_get calls on the same channel
- a mixture of any of the above

I assume exactly one channel here, which is possibly accessed from 
multiple threads.

The only unproblematic case is the simple ca_put, as it is fire and 
forget; for ca_monitor I happen to know that multiple subscriptions are 
fine and each subscription get its own callback on each event. Do the 
other calls behave similarly, i.e. if I fire two ca_get_callback on the 
same channel in a row, do I get two callbacks, too? Are there any 
combinations which will fail ("sorry, pv is active")? I remember 
reading some time ago that only one *db*_put_callback can be active at 
a time on a record (on the IOC), so will interleaving two 
ca_put_callbacks also fail? What if I interleave a synchronous ca_get 
(i.e. I wait for completion using ca_pend or somesuch) with a ca_get or 
ca_get_callback issued by another thread?

Cheers (head smoking)
Ben
-- 
"Never confuse what is natural with what is habitual."
                                   -- attributed to Mahatma Gandhi

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System