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I am looking for a way to monitor the state of one of my applications on OS X. There's a number of components that I need to monitor such as the status of various communication channels. If they go down, the monitoring process should be able to warn the user both on screen and via a push notification.

XPC services look promising, but if the app crashes, I presume this will take out the service as well, or am I mistaken?

My preferred solution is something which would also monitor for unexpected termination, and restart the app if it happens.

What is the best way to do this?

cms
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user2002649
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4 Answers4

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I think monitoring communication channels, etc. must be done by the each specific components (processes). And if the unexpected error occur that component should exit immediately to ensure proper cleanup.

For processe monitoring, below Apple Technical Q&A document will be really helpful:
Technical Note TN2050: Observing Process Lifetimes Without Polling

9dan
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You could write an app which starts your main application as a child process, and waits for it to exit. It could check the exit code, and then react according to your needs.

This approach is explained here: https://stackoverflow.com/a/78095/785411

To fork() some monitoring process to run your main application as a child process, this is explained here: https://stackoverflow.com/a/4327062/785411

Community
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Chris McGrath
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I think you could possibly make use of the built in facilities Launchd and CrashReporter to achieve your requirements.

Launchd is the OS X system supervisor intended for launching and monitoring background processes, and would be typically used to run XPC services. Launchd agents can react to various system events, and can be configured to restart processes in the event of them crashing ( specified via the KeepAlive/SuccessfulExit key in the property list)

Launchd can be set to react to various system events as launch event, including monitoring files and directories, scheduled times, or listening to network connections.

CrashReporter is the OS X system facility that catches and logs all process crashes. It logs through the AppleSystemLogger facility and can be accessed with the syslog tools as documented in the linked TechNote. On Mountain Lion, user process crash reports end up in ~/Library/DiagnosticReports/ , with a crashlog and plist file pair created per crash event.

I think you could use these features in a couple of ways to achieve your requirement, if launchd is responsible for running the xpc services, it can take reponsibility for restarting them on crash events, and they can be dissociated from any app crashes.

You could write a launchd agent that responds to for crash events by montioring the crash report directory (e.g. using the QueueDirectories property) for new logs and re-launches your applicaton, or presents notifications.

cms
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If each process runs in its own thread you could run a watchdog program that monitors whether the threads are alive. A script that runs ps in a loop and parses the output could do it.

You can see the various options here. See for example -C to select by command name, and -m to show all threads.

Floris
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