Advanced Mac OS X Programming: The Big Nerd Ranch Guide

For the More Curious: Run Loop Observers

You can hook more stuff into the run loop, such as an observer. A run loop observer has its callback function invoked at a number of well defined places, shown Figure 15.6. These are the observation points:

• When the run loop is entered

• Before timers are fired

• After timers are fired

• Before sources (like the CFSocket) are checked

• Before the run loop waits for activity (blocking until it can do something)

• After it wakes up

• When the run loop exits

Figure 15.6  Run loop observation points

Here is a function that will register an observer:

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