Experimental Physics and
Industrial Control System

Benjamin Franksen <[email protected]> · Sun, 9 Nov 2014 04:05:58 +0100

Am Freitag, 7. November 2014, 15:24:34 schrieb Andrew Johnson:
> Hi Lewis,
>
> On 11/07/2014 11:19 AM, J. Lewis Muir wrote:
> > Thanks for the clarification.  One thing that's still unclear to me
> > is the semantics of callback execution in preemptive mode.  In the CA
> > reference manual section "Thread Safety and Preemptive Callback to User
> > Code" it says,
> >
> >   "When the CA client library invokes a user's callback function, it
> >
> >    will always wait for the current callback to complete prior to
> >    executing another callback function."
> >
> > What exactly does this mean in preemptive mode?
>
> I don't know for sure myself, I was trying to understand that while
> writing my previous response. I started out thinking that it would not
> apply when preemptive callbacks are enabled, but after looking through
> the code of the library now I'm less sure of that. This comment
>                 // only one recv thread at a time may call callbacks
>                 // - pendEvent() blocks until threads waiting for
>                 // this lock get a chance to run
> quite strongly implies that even in preemptive mode the the library will
> serialize all application callbacks, like you suggested:

I remember asking Jeff Hill this question some time ago and he confirmed it.
Howver, note that most certainly this is true only with respect to a single CA
client context.

Cheers
Ben
--
"Make it so they have to reboot after every typo." -- Scott Adams

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System