How to launch and communicate with a window-less and console-less process from a cocoa app?

Question

I am working with the QuickTime API and need to perform a few lengthy (as in hours) operations in the background. Unfortunately, it is not multi-thread friendly, so I am falling back to perform the tasks in a separate process, so all QuickTime related calls can happen in its main thread.

After launching it, I need a way of getting feedback on its progress, since the operations can take very long.

I am unsure of how to do this, specifically:

• Should the separate process be compiled as another cocoa app or a command line tool?
• How to launch it from the main cocoa app?
• How to periodically get an object from it to get status information?
• How to determine when it finished?
• How to avoid showing a window/console when called?
• How to have it part of the .app bundle so that it does not appear as a separate executable to the user?

These are really 6+ questions, but they are very related and very specific, and I think anyone needing to launch external processes (instead of spawning worker threads) can benefit from their answers. Generic code examples would be very helpful.

Answer 1

If it is possible, then implement the functionality in a command line tool, or another form of GUI-less application. For Cocoa applications it is possible to prevent them appearing on the Dock or in the Force Quit dialog, however a command line tool is a single binary file which does that anyway, so that would probably be a better way.

In terms of launching the tool, NSTask & NSPipe are your friends in this endeavour. The tool can definitely be kept inside your main Application's bundle, inside the Resources directory or some such, and then launched when needed. You can use the pipe to communicate back and forth.

I don't have any example code to hand, and its been a long while since I've had occasion to use either of these classes so the information I can give is limited, but it should be enough to point you in the right direction.