The sporadic (SCHED_SPORADIC) scheduling policy is generally used to provide a capped limit on the execution time of a thread within a given period of time.
This behavior is essential when Rate Monotonic Analysis (RMA) is being performed on a system that services both periodic and aperiodic events. Essentially, this algorithm allows a thread to service aperiodic events without jeopardizing the hard deadlines of other threads or processes in the system.
Under sporadic scheduling, a thread's priority can oscillate dynamically between a foreground or normal priority and a background or low priority. For more information, see “Sporadic scheduling” in the QNX Neutrino Microkernel chapter of the System Architecture guide.