Virtually Exclusive Resources

Independence preservation, a desirable property in realtime locking protocols that isolates tasks from delays due to unrelated critical sections, is formalized. It is shown that independence preservation is impossible if temporary job migrations are disallowed. The OMIP, a new, asymptotically optimal, independence-preserving locking protocol for clustered scheduling based on migratory priority inheritance, is proposed and analyzed. By extending the OMIP to tolerate budget overruns, it is shown that shared resources can be abstracted into virtually exclusive resources (VXRs)—tasks can be provisioned and composed as if they had exclusive access to each resource, even when sharing resources with erroneous tasks. Several practical extensions and applications of VXRs are described. Notably, VXRs enable predictable resource sharing in mixed-criticality systems.