superclass for all monitor control policy objects. PRIORITYCEILINGEMULATION 87 6.1.1 Constructors public Monitor ontrt () 6.1.2 Methods public static void setMonitor Contr l(MonitorControl8 policy) Control the default monitor behavior for object monitors used by synchronized statements and methods in the system. The type of the policy object determines the type of behavior. Conforming implementations must support priority ceiling emulation and priority inheritance for fixed priority preemptive threads. Parameters: policy - The new monitor control policy. If null nothing happens. public static void setMonitor Contr l(java.lang.Object monitor MonitorControl 8 policy) Has the same effect as setMonitorControl(), except that the policy only affects the indicated object monitor. Parameters: monitor - The monitor for which the new policy will be in use. The policy will take effect on the first attempt to lock the monitor after the completion of this method. If null nothing wi...

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Communication in real-time systems has to be predictable, because unpredictable delays in the delivery of messages can adversely affect the execution of tasks dependent on these messages. In this paper, we develop a scheme for providing predictable inter-process communication in real-time systems with (partially connected) point--to--point interconnection networks, which provides guarantees on the maximum delivery time for messages. This scheme is based on the concept of a real-time channel, a unidirectional connection between source and destination. A real-time channel has parameters which describe the performance requirements of the source-- destination communication, e.g., from a sensor station to a control site. Once such a channel is established, the communications subsystem guarantees that these performance requirements will be met. In this paper, we concentrate on methods to compute guarantees for the delivery time of messages belonging to real-time channels. We also address pro...

AbstractÐReal-time middleware services must guarantee predictable performance under specified load and failure conditions, and ensure graceful degradation when these conditions are violated. Guaranteed predictable performance typically entails reservation of resources and use of admission control. Graceful degradation, on the other hand, requires dynamic reallocation of resources to maximize the application-perceived system utility while coping with unanticipated overload and failures. We propose a model for quality-of-service (QoS) negotiation in building real-time services to meet both of the above requirements. QoS negotiation is shown to 1) outperform ªbinaryº admission control schemes (either guaranteeing the required QoS or rejecting the service request), 2) achieve higher application-perceived system utility, and 3) deal with violations of the load and failure hypotheses. We incorporated the proposed QoS-negotiation model into an example real-time middleware service, called RTPOOL, which manages a distributed pool of shared computing resources (processors) to guarantee timeliness QoS for real-time applications. In order to guarantee timeliness QoS, the resource pool is encapsulated with its own schedulability analysis, admission control, and load-sharing support. This support differs from others in that it adheres to the proposed QoS-negotiation model. The efficacy and power of QoS negotiation are demonstrated for an automated flight control system implemented on a network of PCs running RTPOOL. This system is used to fly an F-16 fighter aircraft modeled using the Aerial Combat (ACM) F-16 Flight Simulator. Experimental results indicate that QoS negotiation, while maintaining real-time guarantees, enables graceful QoS degradation under conditions in which traditional schedulability analysis and admission control schemes fail. Index TermsÐQuality-of-service (QoS), QoS negotiation, QoS levels and rewards, schedulability analysis and admission control, automated flight systems. 1

Abstract-We study the problem of guaranteeing synchronous message deadlines in token ring networks where the timed to-ken medium access control protocol is employed. Synchronous bandwidth, defined as the maximum time for which a node can transmit its synchronous messages every time it receives the token, is a key parameter in the control of synchronous message transmission. To ensure the transmission of synchronous messages before their deadlines, synchronous capacities must be properly allocated to individual nodes. We address the issue of appropriate allocation of the synchronous capacities. Several synchronous bandwidth allocation schemes are analyzed in terms of their ability to satisfy deadline constraints of synchronous messages. We show that an inappropriate allocation of the syn-chronous capacities could cause message deadlines to be missed, even if the synchronous traffic is extremely low. We propose

In a distributed environment, tasks often have processing demands on multiple different sites. A distributed task is usually divided up into several subtasks, each one to be executed at some site in order. In a real-time system, an overall deadline is usually specified by an application designer indicating when a distributed task is to be finished. However, the problem of how a global deadline is automatically translated to the deadline of each individual subtask has not been well studied. This paper examines (through simulations) four strategies for subtask deadline assignment in a distributed soft real-time environment. Keywords: soft real-time, distributed systems, deadline assignment, scheduling. 1 Introduction Consider a radar surveillance system whose task is to track flying objects, decide whether an object is friendly or hostile, and in the latter case, come up with a combat strategy. This system requires the cooperation of several different components: a radar sensor componen...

Next generation real-time systems will require greater.flexibility and pre-dictability than is commonly found in today's systems. These future systems include the space station, integrated vision/robotics/AI systems, collections of humans/robots coordinating to achieve common objectives (usually in haz-ardous environments such as undersea exploration or chemical plants), and various command and control applications. The complexity of such systems due to timing constraints, concurrency, and distribution is high. It is accepted that the synchronization, failure atomicity, and permanence properties of trans-actions aid in the development of distributed systems. However, little work has been done in exploiting transactions in a real-time context. We have been at-tempting to categorize real-time data into classes depending on their time, synchronization, atomicity, and permanence properties. Then, using the se-mantics of the data and the applications, we are developing special, tailored, real--time transactions that only supply the minimal properties necessary for that class. This reduces the system overhead in supporting access to various types of data. The eventual goal is to verify that timing requirements can be met.

We study the problem of guaranteeing synchronous message deadlines in communication networks where the timed token medium access control protocol is employed. Synchronous capacity, defined as the maximum time for which a node can transmit its synchronous messages every time it receives the token, is a key parameter in the control of synchronous message transmission. To ensure the transmission of synchronous messages before their deadlines, synchronous capacities must be properly allocated to individual nodes. In this paper, we develop and analyze an optimal synchronous capacity allocation scheme. An optimal scheme can allocate the synchronous capacities in such a way that the synchronous message deadlines are guaranteed if there exists any allocation scheme that can do so. The optimality of the allocation scheme proposed in this paper is formally proved and the bounds for its Worst Case Achievable Utilization are derived. Key Words: Hard Real-Time, Distributed System, FDDI, Timed Token...

Complex distributed tasks often involve parallel execution of subtasks at different nodes. To meet the deadline of a global task, all of its parallel subtasks have to be finished on time. Comparing to a local task (which involves execution at only one node), a global task may have a much harder time making its deadline because it is fairly likely that at least one of its subtasks run into an overloaded node. Another problem with complex distributed tasks occurs when a global task consists of a number of serially executing subtasks. In this case, we have the problem of dividing up the end-to-end deadline of the global task and assigning them to the intermediate subtasks. In this paper, we study both of these problems. Different algorithms for assigning deadlines to subtasks are presented and evaluated. Keywords: soft real-time, distributed systems, parallel systems, deadline assignment, scheduling. 1 Introduction In traditional soft real-time applications, a task is considered a singl...

In a distributed hard real-time system, communications between tasks on different processors must occur in bounded time. The inevitable communication delay is composed of both the delay in transmitting a message on the communications media, and also the delay in delivering the data to the destination task. This paper derives schedulability analysis bounding the media access delay and the delivery delay. Two access protocols are considered: a simple timed token passing approach, and a real-time priority broadcast bus. A simple delivery approach is considered where the arrival of a message generates an interrupt --- the so-called `on demand' approach. 1. INTRODUCTION A hard real-time system is often composed from a number of periodic and sporadic tasks which communicate their results by passing messages; in a distributed system these messages are sent between processors across a communications device. In order to guarantee that the timing requirements of all tasks are met, the communica...