Experimental Physics and
Industrial Control System

Ralph Lange via Core-talk <core-talk at aps.anl.gov> · Fri, 27 Mar 2020 15:54:27 -0000

Re:
> The data pointer dbfl_ref.field can now either point to a copy owned by a
> filter, or it can point to the original data owned by a record. In the
> latter case, the dbfl_ref.dtor is NULL. This required adding
> db_field_log.offset as a new member. It gets initialized, together with the
> no_elements member, by a call to the rset.get_array_info, so we can continue
> to support the wrap-around/ring-buffer feature for array fields.

Careful.
Consider a record that does circular buffering.
While the dbfl is on the queue, the buffer circulates further. Any offset that
is retrieved through rset.get_array_info is volatile and must only be used while
record lock is held. Storing the offset for later use is not appropriate.
The two options for array type dbfl are:
 1. data is owned by the dbfl, contiguous, on the heap (no wrap-around)
    and must be destructed after post-queue processing is done.
 2. data is in the record and post-queue processing retrieves it using
    rset.get_array_info (supporting wrap-around).

Wrap-around must be supported by whatever uses rset.get_array_info. I.e., either
a filter or the post-queue processing copying the array (or a subset) into a
different buffer.
-- 
https://code.launchpad.net/~bfrk/epics-base/+git/epics-base/+merge/381308
Your team EPICS Core Developers is requested to review the proposed merge of ~bfrk/epics-base:zero-size-array-request into epics-base:7.0.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System