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<== Date ==> <== Thread ==>

Subject: Re: write to a single element of an array field
From: Ralph Lange via Core-talk <core-talk at aps.anl.gov>
To: Ben Franksen <benjamin.franksen at helmholtz-berlin.de>
Cc: EPICS Core Talk <core-talk at aps.anl.gov>
Date: Mon, 23 Mar 2020 12:10:06 +0100
On Sun, 22 Mar 2020 at 11:13, Ben Franksen <benjamin.franksen at helmholtz-berlin.de> wrote:
[...]
Here is the the first thing I am seriously stumbling over:

static void db_queue_event_log (evSubscrip *pevent, db_field_log *pLog)
{
    ...
    /*
     * if we have an event on the queue and both the last
     * event on the queue and the current event are emtpy
     * (i.e. of type dbfl_type_rec), simply ignore duplicate
     * events (saving empty events serves no purpose)
     */
    if (pevent->npend > 0u &&
        (*pevent->pLastLog)->type == dbfl_type_rec &&
        pLog->type == dbfl_type_rec) {
        db_delete_field_log(pLog);
        UNLOCKEVQUE (ev_que);
        return;
    }
    ...
}

I don't quite get the logic here. What is (the definition of) an empty
event? And why does dbfl_type_rec indicate that the event is empty?

Probably a bad term.
A dbfl_type_rec update does not contain any data or metadata by itself - that's why I called it "empty". It's just a placeholder, signaling to the post-queue processing that it should use the current state and data of the record, including all metadata and timestamp.
Putting two consecutive dbfl_type_rec events on the queue would lead to an identical update (as all data is taken from the record) being sent twice. Not really useful, that's why I decided it to be safe to drop any consecutive dbfl_type_rec updates.

Cheers,
~Ralph


Replies:
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
Re: write to a single element of an array field Ralph Lange via Core-talk
Re: write to a single element of an array field Ben Franksen via Core-talk

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