Simple and Fast Wait-free Snapshots for Real-time Systems

A wait-free algorithm for implementing a snapshot mechanism for real-time systems is presented in this paper. Snapshot mechanisms give the means to real-time task to read a globally consistent set of variable values while other concurrent tasks are updating them. Such a mechanism can be used to solve a variety of communication and synchronisation problems, including system monitoring and control of real-time applications. Typically, implementations of such mechanisms are based on interlocking. Interlocking protects the consistency of the shared data by allowing only one process at a time to access the data. In a real-time environment locking typically leads to diÆculties in guaranteeing deadlines of high priority tasks because of the blocking. Researchers have introduced non-blocking algorithms and data structures that address the above problems. In this paper we present a simple and eÆcient wait-free (non-blocking) snapshot algorithm by making use of timing information that is available and necessary to the scheduler that schedules the tasks of real-time systems. Experiments on a SUN ENTERPRISE 10000 multiprocessor system show that the algorithm that we propose here, because of its simplicity, outperforms considerably the respective wait-free snapshot algorithm that is not using the timing information.