UDS: A Novel and Flexible Scheduling Algorithm for Deterministic Multithreading

Active replication requires deterministic execution in each replica in order to keep them consistent. Debugging and testing need deterministic execution in order to avoid data races and "Heisenbugs". Beside input, multi-threading constitutes a major source of nondeterminism. Several deterministic scheduling algorithms exist that allow concurrent but deterministic executions. Yet, these algorithms seem to be very different. Some of them were even developed without knowing the others. In this paper, we present the novel and flexible Unified Deterministic Scheduling algorithm (UDS) for weakly and fully deterministic systems. Compared to existing algorithms, UDS has a broader parameter set, allowing for many configurations that can be used to adapt to a given work load. For the first time, UDS defines reconfiguration of a deterministic scheduler at run-time. Further, we informally show that existing algorithms can be imitated by a particular configuration of UDS, demonstrating its importance.