As real-time systems become larger and more complex, attempts to apply the object-oriented paradigm to real-time systems are being made. We introduce a real-time object (RTO) model that is suitable for dynamic real-time environments. We also propose a scheduling algorithm and an implementation of a real-time scheduler for the RTO model. We developed the LLF/MP scheduling algorithm that is good for dynamic real-time environments. A real-time scheduler for the RTO model and LLF/MP scheduling algorithm must guarantee the temporal constraints of both the real-time method and the real-time message, and support an infinite real-time queue efficiently, which LLF/MP needs. To solve these problems, we propose a data structure, RT-HashQ (Real-Time-Hash Queue).

This paper presents an approach to developing Real-time Dependable Systems (RDSs) based on a real-time object model. A system development process can be divided into two phases, that is, Specification Phase and Construction Phase. In the Specification Phase, especially for an RDS, system requirements are decomposed into a group of Real-Time Objects (RTOs) and appropriate objects are identified by means of a decomposition scheme such as Multi-Dimensional Decomposition (MDD). In the Construction Phase, the identified objects are instantiated and combined. RTO.e, which is an extension of the RTO.k model proposed earlier by Kim and Kopetz (1994), plays the role of a connector and also that of a firewall between the two phases. In this paper, we present design tools that are required in developing RDSs. The tools provide a seamless system implementation method and an information base that can be utilized through the development process.

A new reliability model is introduced for selecting the best software fault-tolerant (FT) design. This model uses a task graph technique that allows different candidate FT configurations to be analyzed based on the structure and organization of different distributed embedded systems. Reliability prediction with this approach can be useful for addressing system dependability issues (i.e., fault detection/recovery processes and steady-state availability) in addition to ascertaining fault coverage (i.e., the likelihood of missing and/or false faults). The results of analyzing three different Simplified Unmanned Vehicle System (SUVS) FT configurations are presented. This work is described within the framework of the Conservative and Do-best FT design policies and fits consistent with a software development model for real-time control systems that was introduced in earlier work by the authors.

Several different approaches for implementing conversations in message-based distributed computer systems (DCSs) are discussed. Two different exit control strategies (synchronous and asynchronous) and three different approaches to execution of the conversation acceptance test (centralized, decentralized, and semicentralized) are examined and compared in terms of system performance and implementation cost. An efficient approach to run-time management of recovery information based on an extension of the recovery cache scheme is also discussed. The two major types of conversation structures, name-linked recovery block and abstract data type conversations, are examined to analyze which execution approaches are the most efficient for each conversation structure. As a case study, an unmanned vehicle system is used to illustrate how the approaches can be used in a realistic real-time application.>

Several different approaches are discussed for implementing conversations in loosely coupled distributed computer systems (DCSs). Important implementation factors considered include the control of exits of processes on completion of their conversation tasks and the approach to execution of the conversation acceptance test. Two different exit control strategies, one in a synchronous manner and the other in an asynchronous manner, and three different approaches to execution of the conversation acceptance test, centralized, decentralized, and semi-centralized, are examined and compared in terms of system performance and implementation cost. The effectiveness of these execution approaches also depends on the way conversations are structured initially by program designers. Therefore, the two major types of conversation structures, name-linked recovery block and abstract data type conversations are examined to analyze which execution approaches are the most efficient for each conversation structure. These results provide guidelines for implementing conversations in loosely coupled DCSs.>

The look-ahead execution approach, which allows participant processes that exist early to exit from a conversation before other participants finish their conversation activities, is presented here as a fundamental approach to reducing the synchronization overhead. Queuing network models are developed for both the system operating under the basic conversation execution scheme and the system operating under the look-ahead execution scheme. Based on the models, various performance indicators such as the system throughput, the average number of processors idling inside a conversation due to the synchronization required, and the average time spent in conversation, are evaluated numerically for different application environments. The performance under the look-ahead execution scheme is compared with that under the basic conversation execution scheme. The results provide insights into the extent of benefits provided by the look-ahead execution approach.>

The lookahead execution approach, which allows early finishing participant processes to exit from a conversation before other participants finish their conversation activities, is adopted as a fundamental approach to reducing the synchronization overhead. Queueing network models are developed for both the system operating under the basic conversation scheme and the system operating under the conversation scheme extended with the lookahead capability. Based on the models, various performance indicators such as the system throughput, the average number of processors idling inside a conversation due to the synchronization required, and the average time spent in a conversation are evaluated numerically for different application environments. The performances under the extended scheme are compared to those under the basic conversation scheme. The results provide insights into the extent of benefits that can be brought in by the lookahead execution approach.>