Developing a Mac OS Daemon and IPC

Question

I have developed a dummy Launch Daemon that keeps writing something to the console(syslog) every 5 minutes. Now, I want to write an application that can communicate with this service. By communicating I mean that the user should be able to input the logging frequency(time). For eg, if the service is logging 'Hello world' every 5 minutes, the user should be able to change it to something else (say 2 mins) and the change should be reflected. Any idea on how I should proceed for developing the application and facilitate interprocess communication between the daemon and the application? Thanks.

Answer 1

There are several ways:

1. Have a config file for your application that contains the logging frequency and any other parameters you need. The daemon then parses the file on startup to get its parameters. The daemon also creates a SIGHUP handler, and when it receives a SIGHUP it re-reads the values from the config file. The part that the user interacts with then just gets new parameters from the user, edits them into the config file and sends a kill -HUP to the daemon's process id.

2. The daemon creates a second thread that creates a socket and listens for new parameters, when any arrive, the thread updates variables shared with its main thread which then continues with the new values. The part that interacts with the user then asks the user for new parameters and sends them to the agreed port - you can use nc or netcat to get started and then later code it in C++.