Re: write to a single element of an array field

[Ralph Lange via Core-talk <core-talk at aps.anl.gov>]

Exactly.

That wrap-around feature is needed to handle the case of reading a circular buffer through the array field access API. Record types like the compressRecord keep their array value as a circular buffer, and the first filter (that gets its data from the record) has to be able to cope with that.

~Ralph

On Mon, 23 Mar 2020 at 06:07, Johnson, Andrew N. via Core-talk <core-talk at aps.anl.gov> wrote:

Hi Ben,

The ‘wrap-around’ feature as you describe it sounds like the circular buffer mode of array field access, which Is an essential feature for a few record types such as the histogram record IIRC. I’m not sure if/how it interacts with the filters (there may be bugs in those interactions, I have no idea) but we can’t afford to drop it. I suspect it’s described in the AppDevGuide since it’s been included for a very long time.

- Andrew

--
Complicity is easy, Simplexity takes real work

> On Mar 22, 2020, at 7:23 PM, Ben Franksen via Core-talk <core-talk at aps.anl.gov> wrote:
>
> Some of the filter tests appear questionable to me.
>
> test/ioc/db/dbChArrTest.cpp:144 reads:
>
>    const epicsInt32 res_10_4[] = {14,15,16,17,18,19,10,11,12,13};
>    TEST1(10, 4, "wrapped", res_10_4);
>
> I find this "wrap around" feature surprising. The array filter
> documentation does not mention it.
>
> The reason I am asking about this particular test is, of course, that my
> refactor breaks it. I think I could restore the behavior as expressed by
> the test but before I do that I wanted to ask if it is really intended
> and considered worth keeping.
>
> I should mention that this feature worked only in the dbfl_type_rec case
> and not in the case of dbfl_type_ref. This means that if another filter
> is run before the array filter, and that filter makes a copy of the
> array, then the "wrap around" feature doesn't work anymore.
>
> Cheers
> Ben
>
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