Integration of middleware scheduling and resource management services enables open distributed real-time embedded (DRE) applications to meet end-to-end quality of service (QoS) requirements in highly variable operating environments. This paper describes our research on integrating CORBA scheduling and resource management services, and presents experiments we conducted to validate and quantify the benefits of this integration. Our experimental results show that integrating distributed scheduling and resource management in middleware for open DRE systems can offer significant improvements in predictability. Specifically, integrating our stand-alone resource management service with a previously unmanaged experimental baseline application reduced the ratio of missed deadlines from 26% to 10%, and the same application performed even better under the control of integrated scheduling and resource management services, with a missed deadline ratio of only 1%.

We describe the design and implementation of a static real-time data distribution mechanism that uses a real-time event service and a real-time scheduling service to ensure the ontime, and temporally valid delivery of data. The mechanism implements an algorithm, called the just-in-time data distribution algorithm to determine scheduling parameters that will ensure that data that arrives at a requesting target is valid. We use a navy weapons alignment application to demonstrate the necessity and usefulness of the algorithm and implementation. We also present results of tests that demonstrate that our implementation fulfills the guarantees predicted by the theoretical results.

This paper describes an architecture for real-time multi-agent systems (RTMAS) that builds upon an existing real-time CORBA architecture. The RTMAS architecture provides real-time agent services for real-time agent communication, real-time agent scheduling and real-time agent facilitation. These services work together to allow for the expression and enforcement of real-time agent interactions. The paper describes the design of these services, along with a prototype implementation of the RTMAS architecture that is based upon an existing agent communication implementation.

The paper describes benchmarking for evolvable and adaptable real time command and control systems. MITRE's Evolvable Real-Time C3 initiative developed an approach that would enable current real time systems to evolve into the systems of the future. We designed and implemented an infrastructure and data manager so that various applications could be hosted on the infrastructure. Then we completed a follow-on effort to design flexible adaptable distributed object management systems for command and control (C2) systems. Such an adaptable system would switch scheduling algorithms, policies, and protocols depending on the need and the environment. Both initiatives were carried out for the United States Air Force. One of the key contributions of the work is the investigation of real time features for distributed object management systems. Partly as a result of our work we are now seeing various real time distributed object management products being developed. In selecting a real time distributed object management systems, we need to analyze various criteria. Therefore, we need benchmarking studies for real time distributed object management systems. Although benchmarking systems such as Hartstone and Distributed Hartstone have been developed for middleware systems, these systems are not developed specifically for distributed object based middleware. Since much of our work is heavily based on distributed objects, we developed benchmarking systems by adapting the Hartstone system. The paper describes our efforts in developing benchmarks.

This paper presents a survey of results in developing Real-Time CORBA, a standard for real-time management of distributed objects. This paper includes background on two areas that have been combined to realize Real-Time CORBA: the CORBA standards that have been produced by the international Object Management Group; and techniques for distributed real-time computing that have been produced in the research community. The survey describes major RT CORBA research efforts, commercial development efforts, and standardization efforts by the Object Management Group.

The paper describes an approach to building adaptable real time command and control (C2) systems. In particular it presents an overview of the Adaptable Real-Time Distributed Object Management (ARTDOM) project in progress at the MITRE Corporation. This project is currently developing real time extensions for the Common Object Request Broker Architecture (CORBA) Trading Object Service. The goal of the project is to demonstrate how current C2 systems can be more easily upgraded and made more adaptable by using emerging distributed computing technology. This goal is being accomplished by investigating and developing real time middleware that is reflexive (i.e., capable of examining its current state and processing demands) and self adapting (i.e., capable of reconfiguring itself based on its reflective findings).

Distributed real time applications have presented the need to extend the Object Management Group's (OMG) Common Object Request Broker Architecture (CORBA) standard to support real time. The OMG has formed a real time special interest group (RT SIG) to specify requirements for extending CORBA for real time. One of these requirements involves providing global scheduling of all executions to support end to end timing constraints in the real time CORBA system. The paper describes the design and implementation of a real time scheduling service for a Dynamic Real Time CORBA system.

This paper presents the affected set priority ceiling protocols (ASPCP) for concurrency control in real-time object-oriented systems. These protocols are based on a combination of semantic locking and priority ceiling techniques. This paper shows that the ASPCP protocols provide higher potential concurrency for object-oriented systems than existing priority ceiling protocols, while still bounding priority inversion and preventing deadlock.

The paper describes a concurrency control technique for real-time object-oriented databases that supports logical consistency and temporal consistency, as well as bounded imprecision that results from their trade-offs. The concurrency control technique uses a semantic locking mechanism within each object and user-defined conditional compatibility over the methods of the object. The semantics can specify when to sacrifice precise logical consistency to meet temporal consistency requirements. It can also specify accumulation and bounding of any resulting logical imprecision. The authors show that this technique, under certain general restrictions, can preserve global correctness and bound imprecision by proving it can guarantee a form of epsilon serializability specialized for object-oriented databases.

Presents flexible transaction structuring capabilities that allow related ACID properties (atomicity, consistency, isolation and durability) for better support of real-time transactions. The specification of these flexible transaction structures is demonstrated through proposed extensions to the standard SQL database language.>

The RTC distributed real-time programming system was implemented using AND-OR locking of system resources to meet real-time and concurrency control requirements. Since RTC processes can hold locks while acquiring others, deadlock is possible and therefore a deadlock prevention technique was implemented for AND-OR locking in such systems. The authors briefly discuss the RTC programming system, illustrate the system's use in programming a timed version of the classic dining philosophers example, describe the deadlock prevention technique, and show how it is applied in the RTC dining philosophers example.>

This paper presents a technique that is capable of supporting two major requirements for concurrency control in real-time databases; data temporal consistency, and data logical consistency, as well as tradeoffs between these requirements. Our technique is based upon a real-time object-oriented database model in which each object has its own unique compatibility function that expresses the conditional compatibility of any two potential concurrent operations on the object. The conditions use the semantics of the object, such as allowable imprecision, along with current system state, such as time and the active operations on the object. Our concurrency control technique enforces that allowable concurrency expressed by the compatibility function by using semantic locking controlled by each individual object. The real-time object-oriented database model and process of evaluating the compatibility function to grant semantic locks are described.>

Language constructs for the expression of timing and concurrency requirements in distributed real-time programs are presented. The approach to concurrent real-time programming is to explicitly express real-time concurrency constraints in a program and allow the run-time system to enforce them. To define these constraints precisely, the authors develop a real-time concurrency model that combines an object-based paradigm for the specification of shared resources, a distributed transaction-based paradigm for the specification of application processes, support for timing constraints, and support for precedence ordering. An implementation of the language constructs with real-time scheduling and locking for concurrency control is also described.>

Timed atomic commitment is defined, protocols to implement it in a realistic operating environment are devised, and its usefulness is shown through an example. In a large class of hard-real-time control applications, components execute concurrently on distributed nodes and must coordinate, under timing constraints, to perform the control task. As such, they perform a type of atomic commitment. Traditional atomic commitment differs, however, because there are no timing constraints; agreement is eventual. The authors define timed atomic commitment (TAC), which requires the processes to be functionally consistent, but allows the outcome to include an exceptional state, indicating that timing constraints have been violated. Centralized and decentralized protocols to implement TAC are presented. Programming constructs for TAC are introduced, and their use is illustrated in a coordinating robots example.>

A model and correctness criteria for timed atomic commitment (TAC) are presented which require the processes to be functionally consistent, but allow the outcome to include an exceptional state, indicating that timing constraints have been violated. Correct TAC behavior is defined by presenting an abstract description of the processes involved in the commitment and minimal correctness criteria for their behavior. The correctness criteria capture the intuitive notion that an exception outcome should only occur in the presence of faults, and an aborted outcome should only occur if faults occur or some process votes no. A centralized two-phase commit protocol was modified to meet the correctness criteria by introducing deadlines on the various stages the participants go through (voting and performing), and on the decision phase for the coordinator. The deadlines are derived using several system parameters: maximum message delay, clock drift, and execution time. The protocol is then shown to be correct.>