Error: ‘Read only object or object without ownership can't be applied to mutable function append!’ - mutable

Question

I'm using DolphinDB subscribeTable but the error occurs:
I’d like to know what is wrong with my code. I wanted to subscribe to stream tables in DolphinDB and the code is:
csEngine1=createCrossSectionalEngine(name=sTb_Cs + "_eng",
dummyTable=objByName(sTb_join12),
keyColumn=`symbol,
triggeringPattern="perRow",
useSystemTime=false, timeColumn=`TimeStamp)
subscribeTable(tableName=sTb_join12, actionName="do"+sTb_Cs, offset=-1, handler=append!{csEngine1}, msgAsTable=true, hash=5, reconnect=true)
The UDF handler of another subscription to sTb_join12 also queries csEngine1.
def append_plan (csEngine1, candidates2, strategy, msg){
subscribeTable(tableName=sTb_join12, actionName="do" +strategy, offset=-1, handler=append_plan {csEngine1, candidates2, strategy}, msgAsTable=true, hash=6, reconnect=true)
Please tell why the error occurs and how I can fix it.

Answer 1

The problem is that the parameter in your function (append_plan in this case) was not mutable. With an immutable parameter, the object (csEngine1) will be set to readOnly when calling the function. If another thread writes this object (as shown in your first subscription), it will report the error.
Solution #1
Pass the same hash value in the two subscribeTable functions that subscribe to sTb_join12. With the same hash value, the two subscription tasks will be processed in the same thread in turn, which avoids concurrency and error reporting.
Solution #2
Simplify the two subscribeTable functions into one statement. ‘append!’ the cross-section engine with udf, and then continue with the above process to ensure the append operation and select query to the table CSEngines1 are sequentially processed. You can refer to the following example:
tradesCrossEngine008=createCrossSectionalEngine(name="tradesCrossEngine008", dummyTable=objByName(sTc_join12_testSTR), keyColumn=`Symbol, triggeringPattern=`perRow, useSystemTime=false, timeColumn=`TimeStamp)
def append_plan(msg){
getStreamEngine("tradesCrossEngine008").append!(msg)
select Symbol, rank(left_v1+left_v2) as rmk from getStreamEngine("tradesCrossEngine008")
}
subscribeTable(tableName=sTc_join12_testSTR, actionName="tradesCrossEngine008", offset=0, handler=append_plan, msgAsTable=true, hash=9, reconnect=true)