The current version of Pix4Dmapper for Mac cannot automatically disable the sleep functionality of OS X during processing (i.e. the functionality where the computer goes to sleep after a period of user inactivity.) When the computer is in sleep mode, processing is not continuing.
There are two possible workarounds to avoid the computer to go to sleep:
(Recommended) Use the free utility Caffeine
1. Install the free utility Caffeine from the Mac App Store: https://itunes.apple.com/us/app/caffeine/id411246225?mt=12
2. Activate it only when using Pix4Dmapper.
Disable the "Idle sleep" feature from the System Preferences
1. Go to System Preferences > Energy Saver
2. Select the option Prevent computer from sleeping automatically when the display is off.