This paper reaffirms that fixed-priority with preemption threshold (FPPT) is an important form of real-time scheduling algorithm, which fills the gap between fixed-priority preemptive (FPP) and fixed-priority nonpreemptive (FPNP). When a task set is schedulable by FPPT, there may exist multiple valid preemption threshold assignments, which provide useful scheduling options. All valid assignments form a solution space that is delimited by a minimal and maximal assignment. A mechanism is presented to generate part of the valid assignments once the minimal and maximal assignments are known. The known algorithm to compute the minimal assignment starts at FPP, and the known algorithm to compute the maximal assignment starts from any valid assignment. This paper presents algorithms to compute the minimal and maximal assignments starting from FPNP, and the proofs for the correctness of these algorithms are also presented.

The primary goal of a real-time system is predictability. Achieving this goal requires all levels of the system to work in concert to provide fixed worst-case execution-times. Un-fortunately, many real-time systems are overly restrictive, providing only ad-hoc scheduling facilities and basic concurrent functionality. Ad-hoc scheduling makes developing, verifying, and maintaining a real-time system extremely difficult and time consuming. Basic concurrent functionality forces programmers to develop complex concurrent programs without the aid of high-level concurrency features.Encouraging the use of sophisticated real-time theory and methodology, in conjunction with high-level concurrency features, requires flexibility and extensibility. Giving real-time programmers access to the underlying system data-structures makes it possible to interact with the system to incorporate new ideas and fine-tune specific applications. This paper explores this approach by examining its effect on a selection of crucial real-time issues: real-time monitors, timeouts, dynamic-priority scheduling and basic priority inheritance. The approach is implemented in μC++.