How to notify clients written in c++ that data in kdb+ has changed

Community Support
1

Hi everyone,is there a way to tell clients written in c++ that somethings happenedon the kdb+ server ?Imagine i have got a table called parameters on the kdb+ server. Eachtime the table has changed i want to notify every clients that has aconnection to this server. How can i do this?I know that one can use the function sd1(d,f) to register callbackfunctions in kdb+.Can i solve this problem with the sd1 function?Is there an example?Thanks for any comments or answerKim

2

https://code.kx.com/trac/wiki/Reference/dotzdotvs

Inside .z.vs send an async msg to each client that is interested in changes.

On the c++ side, just listen for changes with 

**int** c = khpu( **"localhost"** , 1234, **"myusername:mypassword"** );_// Connect to a Kdb+ server on the localhost port 1234 ._r = k(c,(S)0);_// read incoming async_
3

Hi Charles,

thx for your quick answer.
But still have problems to understand the code snippet on the client
side.

Using the code:

K r = k(c,(S) 0);

i got a variable called r.

What should i do with r know?
Should i put r in a loop to test for changes?

What should i do when i want to get notified?
No callbacks?

4

Hi Charles,

I tried the solution on my laptop and it works. Not bad.

what is the use case for the sd1 function then?

Sent from my iPhone

5

It’s documented on https://code.kx.com/trac/wiki/Cookbook/InterfacingWithC

CCallbacks

The void sd0(I); and K sd1(I, K(*)(I)); functions are for use with callbacks and are available only within kdb+ itself, i.e. used from a shared library loaded into kdb+.

**sd1** (d,f);

Puts the function K f(I d){..} on the q mainloop given a socket d (or -d for nonblocking). The function f should return (K)0 or a pointer to a kobject and its reference count will be decremented.

sd0(d);

Removes the callback on that socket.