Using only free CPU time with Objective-C program

The BOINC client (does distributed processing jobs like SETI@home does) is able to turn processing on or off based on whether other processes are using a certain percentage of CPU time. That is开发者_开发百科, if the user starts to do some work and their processes start using 60% CPU, BOINC can pause to avoid interfering with the user's work.

I would like to do the same thing (monitor CPU usage by other processes). The difficulty as I see it is not monitoring CPU usage, but rather making sure that the information isn't skewed by my own usage. For example, if my process is using a ton of CPU time it may prevent another process from using enough to trigger the pause.

Can someone point me in the right direction? Even a suggestion for what to search for would be useful. I'm not really sure what this feature would be called.

You can use NSTask to set the 'nice' value of the process when your process starts.

Also [[NSThread mainThread] setThreadPriority:0.0]

where priority value is between 0.0 and 1.0 is a Cocoa API which may save you frakking about with sudo