PCAS: ENUM string table cache is not updated on DBE_PROPERTY updates

[Ralph Lange]

From Wang Xiaoqiang (PSI) <xiaoqiang.wang _AT_ psi.ch>:

TL;DR: When DBE_PROPERTY event is posted in a PCAS application for an Enum typed PV, the client will be noticed but with the stale state strings.

I have create an enum typed PV “MTEST:ENUM", initially with two states [ZERO, ONE], in a PCAS(py) application.
Then this is how I expand it to 3 states and send the DBE_PROPERTY event.
// pseudo code, only to show the sequence
dd = app_table.getDD(gddAppType_dbr_ctrl_enum)
dd[gddAppTypeIndex_dbr_ctrl_enum_value].put(0)
dd[gddAppTypeIndex_dbr_ctrl_enum_enums].put([‘ZERO’,’ONE’,’TWO'])
myPV.postEvent(DBE_PROPERTY, dd)

One the client, I put a monitor with type DBR_GR_ENUM and mask DBE_PROPERTY, and print the states string in the callback.
# a.py
def valueCB(epicsArgs, userArgs):
    print(epicsArgs['pv_statestrings’])

chan1 = CaChannel('MTEST:ENUM')
chan1.searchw()
chan1.add_masked_array_event(ca.DBR_GR_ENUM, None, ca.DBE_PROPERTY, valueCB)
chan1.flush_io()
while True:
    time.sleep(2)

The result is that the callback is called for the property change event, but the state string remains the same.
$ python a.py
('ZERO', 'ONE')
('ZERO', 'ONE’)
If I then run “caget -d DBR_GR_ENUM MTEST:ENUM”, it does print the changed state strings.

However if I load such a mbbo record into IOC,
record(mbbo, "MTEST:ENUM")
{
    field (ZRST, "ZERO")
    field (ONST, "ONE")
}
 and change the state string with "dbpf MTEST:ENUM.TWST TWO”, the client will receive the event with the changed state strings.
$ python a.py
('ZERO', 'ONE')
('ZERO', 'ONE', 'TWO’)

I have doubted the PCASpy implementation. So I tested the above mbbo record through the ca-gateway(2.1.0), the result is consistent with the PCASpy application. It receives the event but with the stale state strings.

The test is with Base 3.14.12.5.

[Ralph Lange (ralph-lange)]

A suggested patch from Wang Xiaoqiang (PSI) <xiaoqiang.wang _AT_ psi.ch>:

I seem to find some clue.

The bug that is reported on launchpad can be worked around by creating a gdd of gddAppType_dbr_ctrl_double type and filling in the meta properties. This has to been do even if there is only a value update.

The bug with the enum typed PV is because casPVI caches the enum string table and only refresh it when PV gets created. So I implemented a fix to update this table during the call of postEvent.
https://github.com/xiaoqiangwang/epics-base/commit/3ca62daa6045d12cc7e71284885309310e9a062e

After these two changes, the DBE_PROPERTY event is properly received by client with updated meta property.

The test I used is here https://github.com/paulscherrerinstitute/pcaspy/blob/master/example/dynamic_property.py
Changing “MTEST:CHANGE” will cause MTEST:ENUM states and MTEST:RAND high alarm limit to change. And this change can be monitored from a client.
$ caput MTEST:CHANGE 3

$ python a.py
('ONE', 'TWO')
('ZERO', 'ONE', 'TWO')

[Ralph Lange (ralph-lange)]

Testing with the CA Gateway (commit 4a1f2b5)
https://github.com/epics-extensions/ca-gateway/commit/4a1f2b508b01d42da0758bb6c03c30db0ed9016e
shows the patch working.

[Ralph Lange (ralph-lange)]

I pushed the patch to the 3.14 branch.
Please update the status for the other branches when the regular merge is done.