POSIX is a set of international standards whose main goal is to support applications portability at the source code level. It defines an operating system interface and environment based on the UNIX operating system. A series of POSIX Real-Time standards have been defined to support real-time applications portability. However, portability is often sacrificed in Real-Time Operating Systems (RTOS) since they must provide predictability and low overhead. In this paper we discuss the POSIX Real-Time Signals Extension and we propose an approach to implement it into a RTOS in order to improve the performance of systems where the execution entities are threads instead of processes, making a compromise between standard conformance and efficiency. The notion of Signal Owner is presented to avoid ambiguity and assign signal priorities accordingly in priority-based systems and to minimize overhead. Also, we discuss the consequences of the defined default POSIX signal actions in real-time systems and the implementation of signal queueing in the Minimal Real-Time System Profile, and different approaches are presented to address these issues. The paper also describes briefly the implementation of the POSIX Real-Time Signals Extension in RTLinux.

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