An adaptive partition scheduler is a priority-based scheduler that also provides execution time guarantees (fair-share). Execution time guarantees apply to threads or groups of threads when the system is overloaded. When the system is not overloaded, threads are scheduled based strictly on priority, maintaining strict real-time behavior. When the system is overloaded, threads are scheduled based priority of threads that are in a ready state and based on the available guaranteed processor time budget of the adaptive partition associated with each thread.