Re: Filtering messages print on the IOC shell console

[Ben Franksen via Tech-talk <tech-talk at aps.anl.gov>]

Am 26.03.20 um 21:25 schrieb Johnson, Andrew N. via Tech-talk:
> My philosophy about error messages is that any messages from device
> support, drivers or other background thread code should call errlog()
> (or epicsPrintf()” which a synonym for that) to report runtime
> errors. That way eltc can be used to silence them and they should
> still be logged if the IOC is connected to a log-server. The only
> place IOC code should be using printf() or fprintf(stderr, …) is when
> reporting errors from initialization commands that were run in a
> startup script or from the command-line (those should not use
> errlog() because the output gets out of sync since it has to pass
> through the logging system before being printed).

Right. And furthermore, as me and others have been preaching for years,
all such modules should (at runtime and by default) print error messages
only if the condition that causes the problem /changes/ and not every
time some record gets processed!

Both asyn and streamdevice nowadays behave this way: you get a single
message (for each record) when accessing the device fails and another
one when it works again and nothing in between (assuming the reason the
error happens stays the same, such as a lost connection).

This is really not hard to achieve. All you need to do is enumerate the
possible error states, track the current state in a struct or class
member associated with the device, and then print messages only when the
new state is different from the stored one /or/ the user has expressly
enabled verbose error output in some driver specific way. Spending this
little bit of extra effort makes life for your users so much easier.

Cheers
Ben

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