Multi-resource Real-Time Reader/Writer Locks for Multiprocessors

A fine-grained locking protocol permits multiple locks to be held simultaneously by the same task. In the case of real-time multiprocessor systems, prior work on such protocols has considered only mutex constraints. This unacceptably limits concurrency in systems in which some resource accesses are read-only. To remedy this situation, a variant of a recently proposed fine-grained protocol called the real-time nested locking protocol (RNLP) is presented that enables concurrent reads. This variant is shown to have worst-case blocking no worse (and often better) than existing coarse-grained real-time reader/writer locking protocols, while allowing for additional parallelism. Experimental evaluations of the proposed protocol are presented that consider both schedulability (i.e., the ability to validate timing constraints) and implementation-related overheads. These evaluations demonstrate that the RNLP (both the mutex and the proposed reader/writer variant) provides improved schedulability over existing coarse-grained locking protocols, and is practically implementable.