The QosClass Enum

case Pcntl::Background ;
/** Runs the process after all high-priority ones had ran their courses. */

case Pcntl::Default ;
/** Runs the process after all high-priority processes but before the low-priority ones. */

case Pcntl::UserInteractive ;
/** Runs the process as the highest priority level. */

case Pcntl::UserInitiated ;
/** Runs the process at high priority level but below Pcntl::UserInteractive ones. */