Experimental Physics and
Industrial Control System

"Johnson, Andrew N." <[email protected]> · Sat, 4 Aug 2018 15:43:25 +0000

My assumption is that they’re wanting direct access to a large block of data without copying it. This should safe for DB links because of the IOC locking, as long as they aren’t copying pointers out of the dbAddr or using it outside of the locked record that is requesting it, so I could see us adding another API to the LSET that allows that for link types that can provide it.

I would be wary of just handing out the dbAddr* pointer though, since the link could get changed without any notice, so I would like to add a little more enforcement. Some link types could even use this to provide access to their raw data buffers, so I’m wondering about an API like doLocked() where the caller gives us a function pointer which we call back with a dbAddr*.

Till, would something like that work for your situation?

- Andrew

-- 
Sent from my iPad

> On Aug 2, 2018, at 11:02 PM, Michael Davidsaver <[email protected]> wrote:
> 
>> On 07/31/2018 01:16 PM, Till Straumann wrote:
>> I'm running into the same issue that was discussed here:
>> 
>> https://epics.anl.gov/tech-talk/2017/msg01247.php
>> 
>> Michael's answer (https://epics.anl.gov/tech-talk/2017/msg01268.php)
>> recommends replacing subRecord by aSubRecord -- however, my use case
>> rather fits the first scenario mentioned by Michael: avoiding the overhead of dbGet()
>> 
>> What is the recommended migration path for this case?
> 
> Can you give some more details?  How do you use the dbAddr* which was being returned?
> 
> 
>> I guess I could use
>> 
>>    dbGetNelements(const struct link*)
>>    dbGetLinkDBFtype(const struct link*)
>> 
>> to make sure the target of my link matches the expectations -- but there is
>> no way to access the data the link points to without either making a copy
>> (dbGet) or exploiting internals (which is deprecated/discouraged)
>> 
>> :-(
>> 
>> Like other posters I'm looking for a minimally intrusive (and yet 'safe') solution
>> for a legacy system with not much horse-power.
>> 
>> - Till
> 

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System