1. Server-Side Plugins Andrew Johnson, Ralph Lange
EPICS Fall Collaboration Meeting, October 2011
PSI

2. Motivation Things get faster Not all clients want all updates
Wide use of timing/event systems Clients want to get updates only during “interesting” system states

3. Current Limitations
Update rate / deadband are configured in the database One setup for all clients
Existing timing/event system driver and support
May cause records to process on event
May set time stamps from hardware
No filtering of updates for unrelated records

4. Design Considerations
Channel Access protocol compatibility Changes create a lot of trouble
Modularity Small systems need small footprint
API Compatibility Don’t break existing “3rd party” code

5. Server-Side Plugins Stackable modules Configuration and Instantiation
Channel Access Client 1
Channel Access Client 2
Client
Stackable modules
Inserted below or above the event queue between database and Channel Access server
Configuration and Instantiation
Client uses JSON modifiers in PV name
Plug-in framework parses configuration and calls filter function
Ethernet
IOC
Channel Access Server
Event Task 1
Event Task 2
Post-Event-Queue Filters
Event Queue
ring buffer
Event Queue
ring buffer
Event Queue
ring buffer
One set of event queues per client
Record processing or field changes cause event updates
Pre-Event-Queue Filters
Record
Event Subscription field 1 flags
Event Subscription field 2 flags
Event Subscription field 3 flags
Event Subscription field 1 flags
MLIS field 1
field 2 field 3 …

6. Plugin Integration Plugin registers its interface (at boot-up):
Name and interface (jump table)
Filter function (and private pointer argument) to be inserted into the pre- or post-event-queue chain
Description of the configuration options and config value locations
Framework
Creates the plugin instance
Parses the configuration and stores results
Calls the registered filter function when appropriate

7. Plugins May Manipulate the data
Manipulate the meta data (alarm, timestamp)
Change the type of data
Change the size of arrays
Drop updates
Insert updates

8. ts – Timestamp “Now” myPv.A{”ts”:{}}
Pre-event-queue: Sets the timestamp of the data update to “now”
Works around the issue that updates to fields which do not cause record processing create data updates that always show the (older) record timestamp, leading to e.g. the archiver creating wrong entries

9. dbnd – Deadband Throttling
myPv.RVAL{”dbnd”{”m”:”rel”,”d”:7.5}}
Pre-event-queue: Deadband throttling similar to analog records
Client specifies absolute or relative (%) delta
Works for any field, not just .VAL

10. arr – Array Subset myArray.VAL{”arr”:{”s”:-5,”i”:2}}
Post-event-queue: Creates a sub-array with given start, increment, stop
Shorthand notation for convenience

11. sync – Sync with Timing System
myPv.VAL{”sync”:{”m”:”while”,”s”:”red”}}
Pre-event-queue: Synchronizes updates with timing system by pushing the update only under certain conditions
Refers to IOC globally configured named states that are defined by timing system events

12. sync Options my.VAL Client subscribes to Client gets
Record my processing
State “red”
Timing events
#17
#42
#17
#42

13. sync Options: before my.VAL{”sync”:{”m”:”before”,”s”:”red”}}
Client subscribes to
my.VAL{”sync”:{”m”:”before”,”s”:”red”}}
Client gets
Record my processing
State “red”
Timing events
#17
#42
#17
#42

14. sync Options: first my.VAL{”sync”:{”m”:”first”,”s”:”red”}}
Client subscribes to
my.VAL{”sync”:{”m”:”first”,”s”:”red”}}
Client gets
Record my processing
State “red”
Timing events
#17
#42
#17
#42

15. sync Options: last my.VAL{”sync”:{”m”:”last”,”s”:”red”}}
Client subscribes to
my.VAL{”sync”:{”m”:”last”,”s”:”red”}}
Client gets
Record my processing
State “red”
Timing events
#17
#42
#17
#42

16. sync Options: after my.VAL{”sync”:{”m”:”after”,”s”:”red”}}
Client subscribes to
my.VAL{”sync”:{”m”:”after”,”s”:”red”}}
Client gets
Record my processing
State “red”
Timing events
#17
#42
#17
#42

17. sync Options: while my.VAL{”sync”:{”m”:”while”,”s”:”red”}}
Client subscribes to
my.VAL{”sync”:{”m”:”while”,”s”:”red”}}
Client gets
Record my processing
State “red”
Timing events
#17
#42
#17
#42

18. sync Options: unless my.VAL{”sync”:{”m”:”unless”,”s”:”red”}}
Client subscribes to
my.VAL{”sync”:{”m”:”unless”,”s”:”red”}}
Client gets
Record my processing
State “red”
Timing events
#17
#42
#17
#42

19. Status Framework in place, interfaces stabilizing
ts, dbnd, arr, sync plugins: implemented
Unit tests for framework and plugins exist
Working on: rate based throttling
Planned: atomic put/get, array stats, default configuration values through info tags

20. Status Unclear: access security integration
3.14 code is available (please give feedback): lp:~ralph-lange/epics-base/server-side-plugins
Framework being merged into 3.15 trunk
Acknowledgements:
Michael Davidsaver
Supported by Helmholtz-Zentrum Berlin / BESSY II