On Deciding Readiness and Failure Equivalences for Processes

In this paper, we study the complexity of deciding readiness and failure equivalences for finite state processes and recursively defined processes specified by normed context-free grammars (CFGs) in Greibach normal form (GNF). The results are as follows: (1) Readiness and failure equivalences for processes specified by normed GNF CFGs are both undecidable. For this class of processes, the regularity problem with respect to failure or readiness equivalence is also undecidable. Moreover, all these undecidability results hold even for locally unary processes. In the unary case, these problems become decidable. In fact, they are Π^p₂-complete, We also show that with respect to bisimulation equivalence, the regularity for processes specified by normed GNF CFGs is NL-complete. (2) Readiness and failure equivalences for finite state processes are PSPACE-complete. This holds even for locally unary finite state processes. These two equivalences are co-NP-complete for unary finite state processes. Further, for acyclic finite state processes, readiness and failure equivalences are co-NP-complete and they are NL-complete in the unary case. (3) For finite tree processes, we show that finite trace, readiness, and failure equivalences are all L-complete. Further, the results remain true for the unary case. Our results provide a complete characterization of the computational complexity of deciding readiness and failure equivalences for several important classes of processes.     

Priority systems with many identical processes

In this paper, we consider the termination problem for systems with an arbitrary number of identical priority finite-state processes. In our model, the number of finite-state processes involved in the computation is arbitrary, and a priority is assigned to each transition of a process to indicate the degree of importance or urgency. We show that the termination problem is undecidable for such systems, even when the underlying interprocess communication structure is a star. The undecidability result holds for systems with acyclic processes as well. However, if we require that no two processes reside in the same state (except the starting state) during the course of the computation, the termination problem is PSPACE-complete. Finally, we show that if the priority relation is empty, the problem becomes PTIME-complete.     

Communication facilities for distributed transaction-processingsystems

The study of communication designs in the context of the Raid system, a robust and adaptable distributed database system for transaction processing, is discussed. Related research work on local interprocess communication, remote interprocess communication, and communication protocols for both local area and wide area networks is briefly summarized. A series of experiments on the performance of the facilities available for building the Raid communication software is described. Raid's communication software, called Raidcomm, has evolved as a result of the knowledge gained both from other systems and from the authors' experiments. Several communication services and mechanisms that can be used to make Raid efficient are identified     

Proof systems for message-passing process algebras

We give sound and complete proof systems for a variety of bisimulation based equivalences over a message-passing process algebra. The process algebra is a generalisation of pureCCS where the actions consist of receiving and sending messages or data on communication channels; the standard prefixing operatora.p is replaced by the two operatorsc?x.p andc!e.p and in addition messages can be tested by a conditional construct. The various proof systems are parameterised on auxiliary proof systems for deciding on equalities or more general boolean identities over the expression language for data. The completeness of these proof systems are thus relative to the completeness of the auxiliary proof systems.     

Decidability of infinite-state timed CCP processes and first-order LTL

The ntcc process calculus is a timed concurrent constraint programming (ccp) model equipped with a first-order linear-temporal logic (LTL) for expressing process specifications. A typical behavioral observation in ccp is the strongest postcondition (sp). The ntcc sp denotes the set of all infinite output sequences that a given process can exhibit. The verification problem is then whether the sequences in the sp of a given process satisfy a given ntcc LTL formula.

This paper presents new positive decidability results for timed ccp as well as for LTL. In particular, we shall prove that the following problems are decidable: (1) the sp equivalence for the so-called locally-independent ntcc fragment; unlike other fragments for which similar results have been published, this fragment can specify infinite-state systems, (2) verification for locally-independent processes and negation-free first-order formulae of the ntcc LTL, (3) implication for such formulae, (4) Satisfiability for a first-order fragment of Manna and Pnueli's LTL. The purpose of the last result is to illustrate the applicability of ccp to well-established formalisms for concurrency.     

Trace Machines for Observing Continuous-Time Markov Chains

In this paper, we study several linear-time equivalences (Markovian trace equivalence, failure and ready trace equivalence) for continuous-time Markov chains that refer to the probabilities for timed execution paths. Our focus is on testing scenarios by means of push-button experiments with appropriate trace machines and a discussion of the connections between the equivalences. For Markovian trace equivalence, we provide alternative characterizations, including one that abstracts away from the time instances where actions are observed, but just reports on the average sojourn times in the states. This result is used for a reduction of the question whether two finite-state continuous-time Markov chains are Markovian trace equivalent to the probabilistic trace equivalence problem for discrete-time Markov chains (and the latter is known to be solvable in polynomial time).     

Unifying behavioral equivalences of timed transition systems

Timed transition systems are one of the most popular real-time models for concurrency. In the paper, various behavioral equivalences of timed transition systems are defined and studied. In particular, categories of this model are constructed, and their properties are studied. In addition, based on the open maps concept, abstract characterization of the considered equivalences is given. Such an approach makes it possible to develop a metatheory designed for unified definition and study of timed behavioral equivalences in the “linear time-branching time” spectrum of semantics.     

Perseus: Retrospective on a portable operating system

We describe the operating system Perseus, developed as part of a study into the issues of computer communications and their impact on operating system and programming language design. Perseus was designed to be portable by virtue of its kernel-based structure and its implementation in Pascal. In particular, machine-dependent code is limited to the kernel and most operating systems functions are provided by server processes, running in user mode. Perseus was designed to evolve into a distributed operating system by virtue of its interprocess communication facilities, based on message-passing. This paper presents an overview of the system and gives an assessment of how far it satisfied its original goals. Specifically, we evaluate its interprocess communication facilities and kernel-based structure, and discuss its portability. We close with a brief history of the project, pointing out major milestones and stumbling blocks.     

Primitives for distributed computing in a heterogeneous local areanetwork environment

Epsilon is a testbed for monitoring distributed applications involving heterogeneous computers, including microcomputers, interconnected by a local area network. Such a hardware configuration is usual but raises difficulties for the programmer. First, the interprocess communication mechanisms provided by the operating systems are rather cumbersome to use. Second, they are different from one system to another. Third, the programmer of distributed applications should not worry about system and/or network aspects that are not relevant for the application level. The authors present the solution chosen in Epsilon. A set of high-level communication primitives has been designed and implemented to provide the programmer with an interface independent of the operating system and of the underlying interprocess communications facilities. A program participating in a distributed application can be executed on any host without any change in the source code except for host names     

Equivalences for a biological process algebra

This paper investigates Bio-PEPA, the stochastic process algebra for biological modelling developed by Ciocchetta and Hillston. It focuses on Bio-PEPA with levels where molecular counts are grouped or concentrations are discretised into a finite number of levels. Basic properties of well-defined Bio-PEPA systems are established after which equivalences used for the stochastic process algebra PEPA are considered for Bio-PEPA, and are shown to be identical for well-defined Bio-PEPA systems. Two new semantic equivalences parameterised by functions, called g-bisimilarity and weak g-bisimilarity are introduced. Different functions lead to different equivalences for Bio-PEPA. Congruence is shown for both forms of g-bisimilarity under certain reasonable conditions on the function and the use of these equivalences are demonstrated with a biologically-motivated example where two similar species are treated as a single species, and modelling of alternative pathways in the MAPK kinase signalling cascade.     

一种带有断开恢复功能的Socket通信方法*

Socket是UNIX平台上网络编程的基础,Socket API提供了进程之间的通信功能,但如果通信的一方发生故障重新启动,通信连接就会断开,应用层必须显式地重新建立连接才可以继续通信。对传统Socket通信机制进行了综合分析,在保证效率的前提下,提出了一种新型的Socket通信方法。采用这种方法,可以为分布在网络上不同主机上的进程间通信提供具有故障恢复能力的可靠通信。     

Experience with PMS-Prolog: A distributed,coarse-grain-parallel prolog with processes,modules and streams

PMS-Prolog is an implementation of Prolog designed for distributed systems, and therefore uses coarsegrain parallelism in preference to the fine-grain parallelism of other implementations. Prolog processes are formally defined and interprocess communication is explicit. An overview of PMS-Prolog is provided, followed by an examination of the PMS-Prolog solutions to four problems. These solutions are also compared to other solutions from the literature. From this, the strengths and weaknesses of the PMS-Prolog model can be seen. Avenues for improving the model are then suggested.     

State Restoration in Systems of Communicating Processes

In systems of asynchronous processes using messagelists with SEND–RECEIVE primitives for interprocess communication recovery primitives are defined to perform state restoration: MARK saves a particular point in the execution of the program; RESTORE resets the system state to an earlier point (saved by MARK); and PURGE discards redundant information when it is no longer needed for possible state restoration.     

一种面向嵌入式系统的进程间消息信方法的设计

描述了具有典型意义的多CPU嵌入式系统的体系结构,详细介绍了一种应用于此种嵌入式系统的分布式操作系统进程间消息通信的方法,又将此方法和常用的分布式操作系统的进程间消息通信方法进行了比较。     

LINUX进程间通信的模型检测

模型检测是一种强大的自动分析验证技术.分析了LINUX进程间通信的部分源代码并进行手工形式化建模,使用有限状态自动机描述模型,继而转换成SPIN的输入语言PROMELA,对其进行模型检测,验证了系统的有界性和可终止性,并就进程间通信中容易发生的问题提出了改进方案.     

An attribute grammar approach to compiler optimization of intra-module interprocess communication

Earlier work has shown the effectiveness of hand-applied program transformations optimizing high-level interprocess communication mechanisms. This paper describes the static analysis techniques necessary to ensure correct compiler application of the optimizing transformations. These techniques include both dataflow analysis and interprocess analysis. This paper focuses on the analysis of communication mechanisms within program modules; however, the analysis techniques can be generalized to handle inter-module optimization analysis as well. The major contributions of this paper include the application of dataflow analysis and the extension of interprocedural analysis—interprocess analysis—to real concurrent programming languages and, more specifically, to the optimization of interprocess communication and synchronization mechanisms that use both static and dynamic channels. In addition, the use of attribute grammars to perform interprocess analysis is significant. This paper also describes an implementation of both intra-process dataflow and interprocess analysis techniques using attribute grammars.This work was supported by NSF under Grant Number CCR88-10617.     

Trace and Testing Equivalence on Asynchronous Processes

We study trace and may-testing equivalences in the asynchronous versions of CCS and π-calculus. We start from the operational definition of the may-testing preorder and provide finitary and fully abstract trace-based characterizations for it, along with a complete in-equational proof system. We also touch upon two variants of this theory by first considering a more demanding equivalence notion (must-testing) and then a richer version of asynchronous CCS. The results throw light on the difference between synchronous and asynchronous communication and on the weaker testing power of asynchronous observations.