Experimental Physics and
Industrial Control System

"Wang Xiaoqiang (PSI)" <[email protected]> · Fri, 29 Dec 2017 22:14:42 +0000

Hi Jamie,

I couldn’t verify the problem in the holiday season. Could you try out the current git source. I have some un-released changes in this direction.

Sent from my iPhone

> On 29 Dec 2017, at 23:08, Jameson Graef Rollins <[email protected]> wrote:
> 
> Hi, Xiaoqiang.  I'm trying to understand when exactly driver.updatePVs()
> needs to be called.  The reference documentation [0] implies that it
> needs to be called after any setParam() call in order for clients to see
> the update.  However, if I overload driver.write() and include some
> setParam() calls, as far as I can tell it doesn't matter if I call
> updatePVs() at the end or not, the behavior seems to be the same.
> 
> The peculiar thing I'm worried about is that in my current application
> there are, under some circumstances, multiple record updates during a
> single driver.write().  For example, before pcaspy 0.7.0, I was doing
> something like this:
> 
> class MyDriver(pcaspy.Driver):
>    ...
>    def write(self, channel, value):
>        ...
>        self.setParam(channel, value)
>        self.setParam(other_channel, other_value)
>        ...
>        self.pvDB[channel].flag = False
>        self.updatePVs()
>        return True
> 
> The 'pvDB[channel].flag = False' was to prevent subscribed clients from
> seeing multiple updates for the primary record 'channel'.  In 0.7.0, it
> seems that neither that, nor the final updatePVs() call are necessary.
> However, I am now occasionally (less than 50% of the time) seeing
> multiple client updates for the primary channel.  The sporadic nature of
> the double updates makes me think there's some kind of race condition.
> Regardless, I can't figure out what's going on, and how to uniformly
> prevent redundant update in subscribed clients.
> 
> Any advice would be much appreciated.
> 
> jamie.
> 
> [0] http://pcaspy.readthedocs.io/en/latest/api.html?highlight=updatePVs

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System