Conflict-Tolerant Real-Time Features

Lecture Notes in Computer Science, 1992

1996

In multiprocessor systems, the worst-case execution time of a task that exclusively accesses a shared resource is unavoidably prolongedas the number of contending processors is increased. In case of function-distributed multiprocessors, because many of the tasks can be processed without synchronizing with other processors, it is advantageous that their worst-case behavior are independent of the number of processors in the system. This paper summarizes the required properties on scalable real-time kernels and discusses their realization techniques. What we have solved so far are described, and the remaining problem to be solved is presented.

IEEE Transactions on Systems, Man, and Cybernetics, 1993

The Cooperative Intelligent Real-time Control Architecture (CIRCA) is a novel architecture for intelligent real-time control that can guarantee to meet hard deadlines while still using unpredictable, unrestricted AI methods. CIRCA includes a real-time subsystem used to execute reactive control plans that are guaranteed to meet the domain's real-time deadlines, keeping the system safe. At the same time, CIRCA's AI subsystem performs higher-level reasoning about the domain and the system's goals and capabilities, to develop future reactive control plans. CIRCA thus aims to be intelligent about real-time: rather than requiring the system's AI methods to meet deadlines, CIRCA isolates its reasoning about which time-critical reactions to guarantee from the actual execution of the selected reactions. The formal basis for CIRCA's performance guarantees is a state-based world model of agent/environment interactions. Borrowing approaches from real-time systems research, the world model provides the information required to make real-time performance guarantees, but avoids unnecessary complexity. Using the world model, the AI subsystem develops reactive control plans that restrict the world to a limited set of safe and desirable states, by guaranteeing the timely performance of actions to preempt transitions that lead out of the set of states. By executing such \safe" and \stable" plans, CIRCA's real-time subsystem is able to keep the system safe (in the world as modeled) for an indeterminate amount of time, while the parallel AI subsystem develops the next appropriate plan. We have applied a prototype CIRCA implementation to a simulated Puma robot arm performing multiple tasks with real-time deadlines, such as packing parts o a conveyor belt and responding to asynchronous interrupts. Our experimental results show how the system can guarantee to accomplish these tasks under a given set of domain conditions (e.g., conveyor belt speed) and resource limitations (e.g., robot arm speed). Furthermore, because CIRCA reasons explicitly about its own predictable, guaranteed behaviors, the system can recognize when its resources are insu cient for the desired behaviors (e.g., parts are arriving too quickly to be packed carefully), and can then make principled modi cations to its performance (e.g., temporarily stacking parts on a table) to maintain system safety.

2010

Message from the WiP Chair Dear Colleagues, Welcome to Brussels and to the Work-in-Progress (WiP) Session of the 22 nd Euromicro Conference on Real-Time Systems (ECRTS'10). I am pleased to present 15 excellent WiP papers that describe innovative research contributions from the broad field of real-time systems.

Dexa Workshops, 1997

In real•time distributed s)'S(em~. it is desirable to allow read and write accesses Lo occur on replicaLed copies of database files in case of neLwork partitions to increase availability. However. the sysLem should detect munml conllicts among the copies of me database files when sites from diITerelll [larLilions merge to form onc partition. In this paper, we present a timestamp-based algorithm for the detection of both write-wrire and read-write conflicts for a single file in distributed systems during network partitions. Our nlgoritllm allows operations to occur in diITerent network partitions simultaneously. When the siLes from diITerenl partition merge, the algorithm detects and resolves both read-write and wrire-write conflicts willlOUl laking into account the semantics of the O"ansacLions. Once (11C conlliCL<; bave been detected, some reconciliation steps for the resolution of conflicts have also been proposed. Our algorithm will be useful in real-time systems where timeliness of operations is morc important than response time (delayed commit).

ACM SIGSOFT Software Engineering Notes, 1993

Showing that concurrent systems satisfy timing constraints on their behavior is difficult, but may be essential for critical applications. Most methods are based on some form of reachability analysis and require construction of a state space of size that is, in general, exponential in the number of components in the concurrent system. In an earlier paper with L. K. Dillon and J. E. Wileden, we described a technique for finding bounds on the time between events without enumerating the state space, but the technique applies chiefly to the case of logically concurrent systems executing on a uniprocessor, in which events do not overlap in time. In this paper, we extend that technique to obtain upper bounds on the time between events in maximally parallel concurrent systems. Our method does not require construction of the state space and the results of preliminary experiments show that, for at least some systems with large state spaces, it is quite tractable. We also briefly describe the...

Proceedings of the Estonian Academy of Sciences. Engineering, 2005

This part of the paper discusses evolution trends of the theory and technology in timeaware interaction-centred models of computation and in time-aware multiagent systems that foster the emergence of a multidisciplinary environment, capable to support analysis of design decisions at the early development stages of time-critical software-intensive systems.

A Practitioner's Handbook for Real-Time Analysis, by Mark H. KLEIN et al.; Kluwer Academic Publishers; Boston, MA, USA; 1993; xiii + 694 pp.; $95; ISBN: 0-7923-9361-9 iRAT -The introspect Real-Time Analysis Tool,

2008

Abstract: Message from the WIP Chair Dear Colleagues: Welcome to Prague and to the Work In Progress (WIP) session of the 20th Euromicro Conference on Real-Time Systems (ECRTS'08). I am pleased to present to you 17 excellent papers on WIP that describe innovative research contributions in the broad field of real-time and embedded systems. The 17 accepted papers were selected from 23 submissions.