Using consistent subcuts for detecting stable properties

We present a general protocol for detecting whether a property holds in a distributed system, where the property is a member of a subclass of stable properties we call the locally stable properties. Our protocol is based on a decentralized method for constructing a maximal subset of the local states that are mutually consistent, which in turn is based on a weakened version of vectored time stamps. The structure of our protocol lends itself to refinement, and we demonstrate its utility by deriving some specialized property-detection protocols, including two previously known protocols that are known to be effective

The Isis project: Fault-tolerance in large distributed systems

This final status report covers activities of the Isis project during the first half of 1992. During the report period, the Isis effort has achieved a major milestone in its effort to redesign and reimplement the Isis system using Mach and Chorus as target operating system environments. In addition, we completed a number of publications that address issues raised in our prior work; some of these have recently appeared in print, while others are now being considered for publication in a variety of journals and conferences

Detection of global state predicates

The problem addressed here arises in the context of Meta: how can a set of processes monitor the state of a distributed application in a consistent manner? For example, consider the simple distributed application as shown here. Each of the three processes in the application has a light, and the control processes would each like to take an action when some specified subset of the lights are on. The application processes are instrumented with stubs that determine when the process turns its lights on or off. This information is disseminated to the control processes, each of which then determines when its condition of interest is met. Meta is built on top of the ISIS toolkit, and so we first built the sensor dissemination mechanism using atomic broadcast. Atomic broadcast guarantees that all recipients receive the messages in the same order and that this order is consistent with causality. Unfortunately, the control processes are somewhat limited in what they can deduce when they find that their condition of interest holds

Runtime monitoring of timing constraints in distributed real-time systems

Embedded real-time systems often operate under strict timing and dependability constraints. To ensure responsiveness, these systems must be able to provide the expected services in a timely manner even in the presence of faults. In this paper, we describe a run-time environment for monitoring of timing constraints in distributed real-time systems. In particular, we focus on the problem of detecting violations of timing assertions in an environment in which the real-time tasks run on multiple processors, and timing constraints can be either inter-processor or intra-processor constraints. Constraint violations are detected at the earliest possible time by deriving and checking intermediate constraints from the user-specified constraints. If the violations must be detected as early as possible, then the problem of minimizing the number of messages to be exchanged between the processors becomes intractable. We characterize a sub-class of timing constraints that occur commonly in distributed real-time systems and whose message requirements can be minimized. We also take into account the drift among the various processor clocks when detecting a violation of a timing assertion. Finally, we describe a prototype implementation of a distributed run-time monitor.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48087/1/11241_2005_Article_BF01088521.pd

Analysis of snapshot algorithms by time approximation.

Law Chi Hung.Thesis (M.Phil.)--Chinese University of Hong Kong, 2004.Includes bibliographical references (leaves 86-91).Abstracts in English and Chinese.Abstract --- p.iAcknowledgement --- p.ivContents --- p.vList of Figures --- p.viiiList of Tables --- p.xChapter 1 --- Introduction --- p.1Chapter 1.1 --- Motivation --- p.4Chapter 1.2 --- Thesis Organization --- p.7Chapter 2 --- Literature Review --- p.9Chapter 2.1 --- Logical Time --- p.9Chapter 2.1.1 --- Event Model --- p.9Chapter 2.1.2 --- Lamport's Logical Clock --- p.10Chapter 2.1.3 --- Mattern's Vector Time --- p.14Chapter 2.2 --- Snapshot Algorithms --- p.18Chapter 2.2.1 --- Preliminaries --- p.19Chapter 2.2.2 --- Chandy-Lamport --- p.22Chapter 2.2.3 --- Lai-Yang and Mattern --- p.24Chapter 2.2.4 --- Sato --- p.25Chapter 3 --- Ad-hoc Network System --- p.29Chapter 3.1 --- Event Model --- p.30Chapter 3.2 --- Snapshot Problem --- p.32Chapter 4 --- Time Approximation in Distributed Systems --- p.37Chapter 4.1 --- Definitions --- p.38Chapter 4.1.1 --- Preliminary --- p.38Chapter 4.1.2 --- Event Ordering --- p.39Chapter 4.1.3 --- Clock --- p.40Chapter 4.1.4 --- Time Approximation Levels --- p.41Chapter 4.1.5 --- Offline Algorithm --- p.41Chapter 4.2 --- Time Approximation in Static Network Systems --- p.42Chapter 4.2.1 --- Stable Snapshot --- p.43Chapter 4.2.2 --- Snapshot --- p.50Chapter 4.2.3 --- Latest Snapshot --- p.52Chapter 4.2.4 --- Time Approximation Levels --- p.54Chapter 4.3 --- Time Approximation in Ad-hoc Network Systems --- p.54Chapter 4.3.1 --- Snapshot --- p.56Chapter 4.3.2 --- Latest Snapshot --- p.61Chapter 4.3.3 --- Time Approximation Levels --- p.61Chapter 4.3.4 --- Bi-vector Clock --- p.63Chapter 4.3.5 --- Strong Snapshot Problem --- p.67Chapter 5 --- Snapshot Algorithm for Ad-hoc Network Systems --- p.69Chapter 5.1 --- Algorithm --- p.70Chapter 5.1.1 --- Notations --- p.70Chapter 5.1.2 --- Rules of Maintaining Si and Ti in Pi --- p.72Chapter 5.1.3 --- The Properties --- p.73Chapter 5.1.4 --- Algorithm --- p.78Chapter 5.2 --- Enhancements --- p.82Chapter 5.2.1 --- Reduction of Stored States and Exchanged Logs --- p.82Chapter 5.2.2 --- LCC Synchronization --- p.82Chapter 6 --- Conclusion --- p.84Bibliography --- p.86Publications --- p.9

Combating state explosion in the detection of dynamic properties of distributed computations

In the context of asynchronous distributed systems, many important applications depend on the ability to check that all observations of the execution of a distributed program, or distributed computation, satisfy a desired (or undesired) temporal evolution of states, or dynamic property. Examples include the implementation of distributed algorithms, automated testing via oracles, debugging, and building fault-tolerant applications through exception detection and handling. When a distributed program exhibits a high degree of concurrency, the number of possible observations of an execution can grow exponentially, quickly leading to an explosion in the amount of space and time required to check a dynamic property. In the worst case, detection of such properties may be defeated. This is the run-time counterpart of the well-known state explosion problem studied in model checking. In this thesis, we study the problem of state explosion as it arises in the detection of dynamic properties. In particular, we consider the potential of applying well-known techniques for dealing with state explosion from model checking to the case of dynamic property detection. Significant semantic similarities between the two problems means that there is great potential for deriving techniques for dealing with state explosion in dynamic property detection based on existing model checking techniques. However, differences between the contexts in which model checking and dynamic property detection take place mean that not all approaches to dealing with state explosion in model checking may carryover to the run-time case. We investigate these similarities and differences and provide the development and analysis of two approaches for combating state explosion in dynamic property detection based on model checking methods: on-the-fly automata theoretic model checking, and partial order reduction.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Atomic spectrometry update – a review of advances in environmental analysis

This is the 34th annual review of the application of atomic spectrometry to the chemical analysis of environmental samples. This Update refers to papers published approximately between August 2017 and June 2018 and continues the series of Atomic Spectrometry Updates (ASUs) in Environmental Analysis that should be read in conjunction with other related ASUs in the series, namely: clinical and biological materials, foods and beverages; advances in atomic spectrometry and related techniques; elemental speciation; X-ray spectrometry; and metals, chemicals and functional materials. The review is not intended to be a comprehensive overview but selective with the aim of providing a critical insight into developments in instrumentation, methodologies and data handling that represent a significant advance in the use of atomic spectrometry in the environmental science