Q Language - Inter-Process Communication


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KDB+ allows one process to communicate with another process through interprocess communication. Kdb+ processes can connect to any other kdb+ on the same computer, the same network, or even remotely. We just need to specify the port and then the clients can talk to that port. Any q process can communicate with any other q process as long as it is accessible on the network and is listening for connections.

  • a server process listens for connections and processes any requests

  • a client process initiates the connection and sends commands to be executed

Client and server can be on the same machine or on different machines. A process can be both a client and a server.

A communication can be,

  • Synchronous (wait for a result to be returned)

  • Asynchronous (no wait and no result returned)

Initialize Server

A q server is initialized by specifying the port to listen on,

q –p 5001 / command line
\p 5001   / session command

Communication Handle

A communication handle is a symbol that starts with “:” and has the form −

`:[server]:port-number

Example

`::5001              / server and client on same machine
`:jack:5001          / server on machine jack
`:192.168.0.156      / server on specific IP address
`:www.myfx.com:5001  / server at www.myfx.com

To start the connection, we use the function “hopen” which returns an integer connection handle. This handle is used for all subsequent client requests. For example −

q)h:hopen `::5001

q)h"til 5"
0 1 2 3 4

q)hclose h

Synchronous and Asynchronous Messages

Once we have a handle, we can send a message either synchronously or asynchronously.

Synchronous Message − Once a message is sent, it waits on and returns the result. Its format is as follows −

handle “message”

Asynchronous Message − After sending a message, start processing the next statement immediately without having to wait and return a result. Its format is as follows −

neg[handle] “message”

Messages that require a response, for example function calls or select statements, will normally use the synchronous form; while messages that need not return an output, for example inserting updates to a table, will be asynchronous.



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