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Real-Time Systems Symposium (RTSS), 2012 IEEE 33rd

Date 4-7 Dec. 2012

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  • [Front cover]

    Publication Year: 2012 , Page(s): C4
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  • [Title page i]

    Publication Year: 2012 , Page(s): i
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  • [Title page iii]

    Publication Year: 2012 , Page(s): iii
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  • [Copyright notice]

    Publication Year: 2012 , Page(s): iv
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  • Table of contents

    Publication Year: 2012 , Page(s): v - vii
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  • Message from the Chairs

    Publication Year: 2012 , Page(s): viii
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  • Conference Committee

    Publication Year: 2012 , Page(s): ix - xi
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  • Reviewers

    Publication Year: 2012 , Page(s): xii
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  • Keynote

    Publication Year: 2012 , Page(s): xiii
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    Summary form only given. All widely used software and networking abstractions lack temporal semantics. The notion of correct execution of a program written in every widely-used programming language, in nearly every processor instruction-set, and the most widely used networking protocols today does not depend on timing. Timing properties emerge from an implementation, rather than being part of the design. But temporal behavior matters in almost all systems, but most particularly in networked embedded systems, where temporal behavior affects not just the value delivered by a system but also its correctness. This talk will argue that time can and must become part of the semantics of programs and networks. To illustrate that this is both practical and useful, we will describe recent efforts at Berkeley in the design and analysis of timing-centric distributed software systems. In particular, we will focus on the PTIDES project, which provides a timing-centric programming model for distributed real-time systems that leverages recent advances in network time synchronization. View full abstract»

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  • Investigation of Scratchpad Memory for Preemptive Multitasking

    Publication Year: 2012 , Page(s): 3 - 13
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (289 KB) |  | HTML iconHTML  

    We present a multitasking scratchpad memory reuse scheme (MSRS) for the dynamic partitioning of scratchpad memory between tasks in a preemptive multitasking system. We specify a means to compute the worst-case response time (WCRT) and schedulability of task sets executed using MSRS. Our scratchpad-related preemption delay (SRPD) is an analog of cache-related preemption delay (CRPD), proposed in previous work as a way to compute the worst-case cost imposed upon a preempted task by preemption in a multitasking system. Unlike CRPD, however, SRPD is independent of the number of tasks and the local memory size. We compare SRPD with CRPD by experiment and determine that neither dominates the other, i.e. either may be better for certain task sets. However, MSRS leads to improved schedulability versus cache when contention for local memory space is high, either because the local memory size is small, or because the task set is large, provided that the cost of loading blocks from external memory to scratchpad is similar to the cost of loading blocks into cache. View full abstract»

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  • Curbing Aggregate Member Flow Burstiness to Bound End-to-End Delay in Networks of TDMA Crossbar Real-Time Switches

    Publication Year: 2012 , Page(s): 14 - 25
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1277 KB) |  | HTML iconHTML  

    To integrate the nowadays rapidly expanding distributed real-time systems, we need multi-hop real-time switched networks. A (if not "the") widely recognized/adopted real-time switch architecture is the TDMA crossbar real-time (TCRT) switch architecture. However, the original TCRT switch architecture assumes per-flow queueing. To support scalability, however, queue sharing (i.e. flow aggregation), must be allowed. With simple flow aggregation, flow burstiness can grow and infect, making schedulability and end-to-end delay bound analysis an open problem. To deal with this, we propose the real-time aggregate scheme. The scheme complies with the existing TCRT switch architecture, and deploys spatial-temporal isolation and over-provisioning to curb aggregate member flows' burstiness. This allows us to derive the closed-form end-to-end delay bound, and give the corresponding resource planning and admission control strategies. Simulations are carried out to show the effectiveness of the design. View full abstract»

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  • Controlling Preemption for Better Schedulability in Multi-Core Systems

    Publication Year: 2012 , Page(s): 29 - 38
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (315 KB) |  | HTML iconHTML  

    Interest in real-time multiprocessor scheduling has been rekindled as multi-core chips are increasingly used for embedded real-time systems. While tasks may be preemptive or non-preemptive (due to their transactional operations), deadline guarantees are usually made only for those task sets in each of which all tasks are preemptive or non-preemptive, not a mixture thereof, i.e., all or nothing. In this paper, we develop a schedulability analysis framework that guarantees the timing requirements of a given task set in which a task can be either preemptive or non-preemptive. As an example, we apply this framework to the prioritization policy of EDF (Earliest Deadline First), yielding schedulability tests of mpn-EDF (Mixed Preemptive/Non-preemptive EDF), which is a generalization of both fp-EDF (fully-preemptive EDF) and np-EDF (non-preemptive EDF). In addition to their deadline guarantees for any task set that is composed of a mixture of preemptive and non-preemptive tasks, the tests outperform the existing schedulability tests of np-EDF (a special case of mpn-EDF) by up to 109.1%. Using these tests, we also improve schedulability by disallowing preemptions of some preemptive tasks. For this, we develop an algorithm that optimally disallows preemption of a preemptive task under a certain assumption, and demonstrate via simulation that the algorithm discovers up to 30.9% additional task sets that are schedulable with the proposed scheduling scheme, but not with fp-EDF or np-EDF. View full abstract»

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  • Optimal Fixed Priority Scheduling with Deferred Pre-emption

    Publication Year: 2012 , Page(s): 39 - 50
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (707 KB) |  | HTML iconHTML  

    The schedulability of systems using fixed priority pre-emptive scheduling can be improved by the use of non-pre-emptive regions at the end of each task's execution, an approach referred to as deferred pre-emption. Choosing the appropriate length for the final non-pre-emptive region of each task is a trade-off between improving the worst-case response time of the task itself and increasing the amount of blocking imposed on higher priority tasks. In this paper we present an optimal algorithm for determining both the priority ordering of tasks and the lengths of their final non-pre-emptive regions. This algorithm is optimal for fixed priority scheduling with deferred pre-emption, in the sense that it is guaranteed to find a schedulable combination of priority ordering and final non-pre-emptive region lengths if such a schedulable combination exists. View full abstract»

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  • Extending Task-level to Job-level Fixed Priority Assignment and Schedulability Analysis Using Pseudo-deadlines

    Publication Year: 2012 , Page(s): 51 - 62
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (515 KB) |  | HTML iconHTML  

    In global real-time multiprocessor scheduling, a recent analysis technique for Task-level Fixed-Priority (TFP) scheduling has been shown to outperform many of the analyses for Job-level Fixed-Priority (JFP) scheduling on average. Since JFP is a generalization of TFP scheduling, and the TFP analysis technique itself has been adapted from an earlier JFP analysis, this result is counter-intuitive and in our opinion highlights the lack of good JFP scheduling techniques. Towards generalizing the superior TFP analysis to JFP scheduling, we propose the Smallest Pseudo-Deadline First (SPDF) JFP scheduling algorithm. SPDF uses a simple task-level parameter called pseudo-deadline to prioritize jobs, and hence can behave as a TFP or JFP scheduler depending on the values of the pseudodeadlines. This natural transition from TFP to JFP scheduling has enabled us to incorporate the superior TFP analysis technique in an SPDF schedulability test. We also present a pseudo-deadline assignment algorithm for SPDF scheduling that extends the well-known Optimal Priority Assignment (OPA) algorithm for TFP scheduling. We show that our algorithm is optimal for the derived schedulability test, and also present a heuristic to overcome the computational complexity issue of the optimal algorithm. Our simulation results show that the SPDF algorithm with the new analysis significantly outperforms state-of-the-art TFP and JFP analysis. View full abstract»

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  • A Generalized Parallel Task Model for Recurrent Real-time Processes

    Publication Year: 2012 , Page(s): 63 - 72
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (266 KB) |  | HTML iconHTML  

    A model is considered for representing recurrent precedence-constrained tasks that are to execute on multiprocessor platforms. A recurrent task is specified as a directed a cyclic graph (DAG), a period, and a relative deadline. Each vertex of the DAG represents a sequential job, while the edges of the DAG represent precedence constraints between these jobs. All the jobs of the DAG are released simultaneously and need to complete execution within the specified relative deadline of their release. The task may release jobs in this manner an unbounded number of times, with successive releases occurring at least the specified period apart. The scheduling problem is to determine whether such a recurrent task can be scheduled to always meet all deadlines upon a specified number of processors that are dedicated for the use of this task. This problem is shown to be computationally intractable, but amenable to efficient approximate solutions. EDF is shown to be a good approximate scheduling algorithm. Polynomial and pseudo-polynomial schedulability tests, of differing effectiveness, are presented for determining whether a given task can be scheduled by EDF to always meet all deadlines on a specified number of processors. View full abstract»

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  • Distributed Sensing for High Quality Structural Health Monitoring Using Wireless Sensor Networks

    Publication Year: 2012 , Page(s): 75 - 84
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (369 KB) |  | HTML iconHTML  

    In recent years, using wireless sensor networks (WSNs) for structural health monitoring (SHM) has attracted increasing attention. Traditional centralized SHM algorithms developed by civil engineers can achieve the highest damage detection quality since they have the raw data from all the sensor nodes. However, directly implementing these algorithms in a typical WSN is impractical considering the large amount of data transmissions and extensive computations required. Correspondingly, many SHM algorithms have been tailored for WSNs to become distributed and less complicated. However, the modified algorithms usually cannot achieve the same damage detection quality of the original centralized counterparts. In this paper, we select a classical SHM algorithm: the eigen-system realization algorithm (ERA), and propose a distributed version for WSNs. In this approach, the required computations in the ERA are updated incrementally along a path constructed from the deployed sensor nodes. This distributed version is able to achieve the same quality of the original ERA using much smaller wireless transmissions and computations. The efficacy of the proposed approach is demonstrated through both simulation and experiment. View full abstract»

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  • pCruise: Reducing Cruising Miles for Taxicab Networks

    Publication Year: 2012 , Page(s): 85 - 94
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (631 KB) |  | HTML iconHTML  

    In taxicab industry, a long standing challenge is how to reduce taxicab's mileage spent without a fare, i.e., cruising mile. The current solution for this challenge usually requires the participation of the passengers. To solve the issue without the passengers involved, in this paper, we propose a cruising system, pCruise, for taxicab drivers to maximize theirs profits by finding the optimal route to pick up a passenger, thus reducing the cruising mile. In pCruise, base on collected GPS records about other near taxicabs, a taxicab characterizes its cruising process with a cruising graph. When a taxicab becomes vacant and tries to find a passenger, cruising graph will provide the shortest cruising route with at least one expected available passengers for this taxicab. With the shortest cruising routes, taxicabs will significantly reduce theirs cruising miles. We evaluate pCruise based on a 7 days 10 GB real world GPS dataset from a city with more than 15,000 taxicabs. The evaluation results show that pCruise can assist taxicab drivers to reduce cruising miles by 41% on average. View full abstract»

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  • RadioSense: Exploiting Wireless Communication Patterns for Body Sensor Network Activity Recognition

    Publication Year: 2012 , Page(s): 95 - 104
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (613 KB) |  | HTML iconHTML  

    Automatically recognizing human activities in a body sensor network (BSN) enables many human-centric applications. Many current works recognize human activities through collecting and analyzing sensor readings from on-body sensor nodes. These sensing-based solutions face a dilemma. On one hand, to guarantee data availability and recognition accuracy, sensing-based solutions have to either utilize a high transmission power or involve a packet retransmission mechanism. On the other hand, enhancing the transmission power increases a sensor node's energy overheads and communication range. The enlarged communication range in consequence increases privacy risks. A packet retransmission mechanism complicates on-body sensor nodes' MAC layer and hence increases energy overheads. In contrast to the sensing-based solutions, we build Radio Sense, a prototype system that exploits wireless communication patterns for BSN activity recognition. Using Radio Sense, we benchmark three system parameters (transmission (TX) power, packet sending rate, and smoothing window size) to design algorithms for system parameter selection. The algorithms aim to balance accuracy, latency, and energy overheads. In addition, we investigate the minimal amount of training data needed for reliable performance. We evaluate our Radio Sense system with multiple subjects' data collected over a two-week period and demonstrate that Radio Sense achieves reliable performance in terms of accuracy, latency, and battery lifetime. View full abstract»

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  • RASS: A Portable Real-time Automatic Sleep Scoring System

    Publication Year: 2012 , Page(s): 105 - 114
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (358 KB) |  | HTML iconHTML  

    It is a well known fact that the quality of sleep is an important factor in health-related quality of life (HRQoL), and people could prevent potential problems by tracking the quality of their sleep. Unfortunately sleep scoring, which is a systematic way to address the sleep staging as well as the scoring of arousals, respiratory, cardiac, and movement events, is usually conducted with specialized equipment which is expensive and operated by specialists in dedicated sleep centers. Related research studies and products (e.g. ZEO) tried to solve this problem, but they either used multiple probes that cause discomfort to the patient, or could not score in real time. In this paper, we design and implement RASS, a portable Real-time Automatic Sleep Scoring system. RASS only requires one probe, which is inexpensive and, as a result, may be used at home or during travel. RASS accurately scores the sleeping state and detects sleep apnea in real-time based on the sensing results of pulse, blood oxygen, activity, sound and light signals. An alarm will be generated when a severely abnormal sleep state is detected. RASS has been tested with 48 patients, and the test results show that RASS could achieve higher than 84% accuracy. View full abstract»

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  • A PTAS for Assigning Sporadic Tasks on Two-type Heterogeneous Multiprocessors

    Publication Year: 2012 , Page(s): 117 - 126
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    Consider the problem of determining a task-to-processor assignment for a given collection of implicit-deadline sporadic tasks upon a multiprocessor platform in which there are two distinct kinds of processors. We propose a polynomial-time approximation scheme (PTAS) for this problem. It offers the following guarantee: for a given task set and a given platform, if there exists a feasible task-to-processor assignment, then given an input parameter, ϵ, our PTAS succeeds, in polynomial time, in finding such a feasible task-to-processor assignment on a platform in which each processor is 1+3ϵ times faster. In the simulations, our PTAS outperforms the state-of-the-art PTAS and also for the vast majority of task sets, it requires significantly smaller processor speedup than (its upper bound of) 1+3ϵ for successfully determining a feasible task-to-processor assignment. View full abstract»

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  • Efficient Admission Control for Enforcing Arbitrary Real-Time Demand-Curve Interfaces

    Publication Year: 2012 , Page(s): 127 - 136
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (363 KB) |  | HTML iconHTML  

    Server-based resource reservation protocols (e.g., periodic and bandwidth-sharing servers) have the advantage of providing temporal isolation between subsystems co-executing upon a shared processing platform. For many of these protocols, temporal isolation is often obtained at the price of over-provisioned reservations. Other more fine-grained approaches such as real-time calculus permit a precise characterization of the resources required by a subsystem via demand-curve interfaces. However, an important, unsolved challenge for subsystems specified by such interfaces is the development of efficient enforcement techniques to guarantee temporal isolation between the subsystems. Admission control algorithms can be used in this regard to ensure that the cumulative subsystem demand never violates the demand-curve specified by the interface. In this paper, we address the challenge by designing admission controllers for complex, arbitrary demand-curve interfaces and proposing enforcement techniques. First, we propose an exact algorithm and show that its complexity is infeasible for long-running systems. To address this drawback, we then design an approximation algorithm and associated enforcement techniques to handle unpredictable execution times. We validate, via simulations, that our approximate approach is significantly more efficient than the exact approach with only minor decrease in the accuracy of the admission controller. View full abstract»

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  • Static Approximation Algorithms for Regularity-based Resource Partitioning

    Publication Year: 2012 , Page(s): 137 - 148
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (534 KB) |  | HTML iconHTML  

    As a hierarchical real-time system framework, the Regularity-based Resource Partition Model allocates physical resources in time intervals determined by integral numbers of a time unit to tasks in different applications. A Regularity-based Resource Partition is characterized by its regularity and availability factor. An important problem is how to schedule a group of resource partitions with the specification of their regularities and availability factors. Mok and Feng have provided the AAF-Single algorithm which works only on a single-resource platform. Li and Cheng have recently extended AAF-Single to AAF-Multi for multiresource platforms without violating the schedulability bound given by Feng. However, the resource utilization of these two algorithms could be significantly improved. This paper is dedicated to developing optimized resource partitioning algorithms for the Regularity-base Resource Partition Model. We first decompose the resource partitioning problem into two sub problems, and invoke the Pfair algorithm to solve the first sub problem. Then we introduce a category of approximation algorithms called Static Approximation Algorithms (SAA) to solve the second sub problem. An SAA adjusts the availability factors of the resource partitions with a specific boundary sequence. We prove that the schedulability bound of any feasible SAA is at most 0.5. Furthermore, we develop an optimal SAA called Magic7. Simulation shows that Magic7-enhanced algorithms improve the resource utilization by 10% or more. View full abstract»

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  • Quantifying the Effect of Rare Timing Events with Settling-Time and Overshoot

    Publication Year: 2012 , Page(s): 149 - 160
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (277 KB) |  | HTML iconHTML  

    For hard real-time systems, worst-case timing models are employed to validate whether timeliness properties, such as meeting deadlines, are always satisfied. We argue that such a deadline-interface should be generalised in view of two separate motivations: (a) applications can tolerate bounded non-satisfaction of timeliness properties due to inherent robustness or relaxed quality requirements, and (b) worst-case timing models do not expose the occurrence of certain rare yet predictable events. As a more expressive interface, we propose the Rare-Event with Settling-Time (REST) model wherein, during rare events nominal timing models can be violated up to a known bound. Such a violation may lead to non-satisfaction of the timeliness properties up to a certain bound. We characterise this bound in terms of (a) the longest interval when the deadlines are not met, which we call the settling-time, and (b) the maximum number of jobs that can miss deadlines during the settling-time called the overshoot. We propose two models of rare events, characterised on an interval domain. For a single stream of jobs, we provide methods to tightly compute the settling-time and overshoot. For multiple streams of jobs on a single processor, we show that amongst schedulers agnostic to the occurrence of the rare event, the EDF scheduler optimally minimises the settling-time. In contrast, RM is not optimal within the class of fixed priority schedulers. View full abstract»

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  • QoS-Based Resource Allocation for Next-Generation Spacecraft Networks

    Publication Year: 2012 , Page(s): 163 - 172
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1147 KB) |  | HTML iconHTML  

    Current spacecraft systems generally have monolithic structures, but a "fractionated" architecture is being considered for next generation spacecrafts. A fractionated spacecraft system is a cluster of independent modules that communicate wirelessly to maintain cluster flight formations and realize the functions usually performed by a monolithic satellite. The envisioned benefits of the fractionated approach include enhanced responsiveness, greater flexibility, robustness and co-existence of multiple missions from different sources with varying degree of trust. The fractionated architecture, however, introduces significant new challenges from the perspective of resource allocation and management. The mobile nature of the clusters and the modules within the cluster implies that the network topology is highly time-varying. A cluster with multiple missions can require messages to be transmitted across the network with varying degrees of QoS requirements such as timeliness and data delivery reliability. The system must determine the appropriate and timely resource allocation for these missions. In this paper, we address these resource allocation challenges by introducing an abstraction of dynamic graphs, and extending the QoS based Resource Allocation Model (Q-RAM) to operate on these dynamic graphs. We develop a mechanism to decompose a dynamic graph into multiple static sub-graphs using which the resource allocation problem is partitioned into multiple sub-problems within each of these static sub-graphs. We have experimentally evaluated our solution by building a simulation framework called SatSim, which can handle a variety of satellite configurations and mobility models. The proposed solution is shown to achieve a near-optimal solution for the resource allocation problem in time-varying networks, while reducing time complexity significantly. View full abstract»

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  • Static and Dynamic Analysis of Timed Distributed Traces

    Publication Year: 2012 , Page(s): 173 - 182
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (273 KB) |  | HTML iconHTML  

    This paper presents an algorithm for checking global predicates from distributed traces of cyber-physical systems. For an individual agent, such as a mobile phone or a robot, a trace is a finite sequence of state observations and message histories. Each observation has a possibly inaccurate timestamp from the agent's local clock. The challenge is to symbolically over approximate the reachable states of the entire system from the unsynchronized traces of the individual agents. The presented algorithm first approximates the time of occurrence of each event, based on the synchronization errors of the local clocks, and then over approximates the reach sets of the continuous variables between consecutive observations. The algorithm is shown to be sound, it is also complete for a class of agents with restricted continuous dynamics and when the traces have precise information about timing synchronization inaccuracies. The algorithm is implemented in an SMT solver-based tool for analyzing distributed Android apps. Experimental results illustrate that interesting properties like safe separation, correct geocast delivery, and distributed deadlocks can be checked for up-to twenty agents in minutes. View full abstract»

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