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Subject: Re: write to a single element of an array field
From: Ralph Lange via Core-talk <core-talk at aps.anl.gov>
To: EPICS Core Talk <core-talk at aps.anl.gov>
Date: Thu, 19 Mar 2020 19:49:10 +0100
A bit of background:

The name db field log was the traditional one. When adding the filters, I started to do a refactoring of the code to use more comprehensive names for some of the core concepts, and trashed it after a few hours, because I was getting commits that changed every line of the code, which I was sure not to get past QAndrew.

Originally, there had to be two types of updates (field logs):
1. scalar data, where the value and all metadata (incl. timestamp) was in the update, and the post-queue processing was copying data from the update.
2. array data, where the update contained a pointer to the record, and the post-queue processing accessed the record to copy the data out. (into the CA buffers)

When adding filters that are able to change the data and metadata of an array, there is a need for a third type:
3. manipulated array data, where the changed metadata is in the update, and the array data is a copy allocated on the heap, i.e. has to be free()d after post-queue processing.

The admittedly weird way this extension was merged into the original db_field_log structure was intended to keep the changes minimally invasive.

*Sigh*. I know.
~Ralph


Replies:
Re: write to a single element of an array field Johnson, Andrew N. via Core-talk
Re: write to a single element of an array field Ben Franksen via Core-talk
References:
Re: write to a single element of an array field Ben Franksen via Core-talk
Re: write to a single element of an array field Ben Franksen via Core-talk
Re: write to a single element of an array field Ben Franksen via Core-talk

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