Hi Lewis,
On 2012-10-02 J. Lewis Muir wrote:
> What is a scenario where the -c option to the EPICS Base caget
> program is useful?
>
> I've used the -c option (asynchronous put--use ca_put_callback
> and wait for completion) of the caput program many times to wait
> for a put to complete (e.g. a motor move to complete), but I
> know caget has the same -c option and I don't know when I would
> use it. (I'd like to test its behavior, but I don't even know
> of a record type or group of records that would let me do that.)
Using ca_get_callback() will give a different result for a 3.14.12 or later
client & server pair if you're requesting an array which is currently shorter
than its maximum possible length (and you give a length request of zero, which
I believe caget -c does now). Earlier versions will return an array which is
as large as the underlying field's storage (e.g. waveform.NELM elements) with
all elements after the valid data set to zero, whereas now you get given an
array the same size as the data (e.g. waveform.NORD elements).
That's the main reason I can think for using it.
HTH,
- Andrew
--
Never interrupt your enemy when he is making a mistake.
-- Napoleon Bonaparte
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