Practical exception handling and resolution in concurrent programs

Two complementary techniques have evolved for providing fault-tolerance in software: forward error recovery and backward error recovery. Few implementations permit both approaches to be combined within a particular application. Fewer techniques are available for the construction of fault-tolerant software for systems involving concurrent processes and multiple processors. Many schemes for supporting forward or backward recovery are based on some concept of an atomic action. The authors propose a mechanism for supporting an atomic action in a system of communicating sequential processes (CSP). The atomic action is used as the basic unit for providing fault-tolerance. The atomic action is called an FT-action, and both forward and backward error recovery are performed in the context of an FT-action.

Multi-core processors are present in everyone's daily life. Consequently, concurrent programming has reemerged as a pressing concern for everyone interested in exploring all the potential computational power in these machines. But, the emergence of new concurrency models and programming languages also brings new challenges in terms of how one can deal with abnormal occurrences, much due to the heterogenous parallel control flow. Unexpectedly, sequential Exception Handling models remain as the most used tool for robustness, even in the most recent concurrent programming languages. Though, the appearance of more complex models, such as programming languages with implicit concurrency, might pose a challenge too big for these sequential mechanisms. In this article we will provide evidences why such models are not generally suited to deal with faults in programs with implicit concurrency and, in the light of more recent advances in concurrent Exception Handling, we will discuss the attributes of a model for addressing this problem.

Architectures based on Coordinated Atomic action (CA action) concepts have been used to build concurrent fault-tolerant systems. This conceptual model combines concurrent exception handling with action nesting to provide a general mechanism for both enclosing interactions among system components and coordinating forward error recovery measures. This paper proposes an architectural model to guide the formal specification of concurrent fault-tolerant systems. This architecture provides built-in CSP (Communicating Sequential Process) processes and predefined channels to coordinate exception handling of the user-defined components. As a result, a formal and general architecture supporting software fault-tolerance are ready to be used.

A rule-based approach to proactive exception handling in business processes

A comparative study of exception handling mechanisms for building dependable object-oriented software

Stephen J. Hartley Oxford University Press, New York, 1998, 260 pp. ISBN 0-19-511315-2, $45.00 Concurrent Programming is a thorough treatment of Java multi-threaded programming for both a stand-alone and distributed environment. Designed mostly for students in concurrent or parallel programming classes, the text is also an excellent reference for the practicing professional developing multi-threaded programs or applets. Hartley first provides a complete explanation of the features of Java necessary to write concurrent programs, including topics such as exception handling, interfaces, and packages. He then gives the reader a solid background to write multi-threaded programs and also presents the problems introduced when writing concurrent programs—namely race conditions, mutual exclusion, and deadlock. Hartley also provides several software solutions that do not require the use of common process and thread mechanisms. Once the groundwork is laid for writing concurrent programs, Hartley then takes a different approach than most Java references. Rather than presenting how Java handles mutual exclusion with the synchronized keyword (although it is covered later), he first looks at semaphore-based solutions to classic concurrent problems such as bounded-buffer, readers-writers, and the dining philosophers. Hartley also uses the same approach to develop Java classes for monitors and message passing. This unique approach to introducing concurrency allows the readers to both understand how Java threads are synchronized and how the basic synchronization mechanism can be used to construct more abstract tools such as semaphores. If there is a shortcoming with the text it is with the lack of sufficient coverage of remote method invocation (RMI), although there is a section covering RMI. This is quite understandable as RMI is a fairly recent phenomenon with the Java community. Also, the classes that Hartley provides could easily implement RMI rather than sockets to handle communication. The strengths of the book include its ease in reading, several examples at the end of chapters, a package similar to Xtango that provides algorithm animation, and a supportive web site by the author (see www.mcs.drexel.edu/~shartley/ConcProgJava/index.html ) including compressed source code. As Java becomes more dominant on the server side of multi-tier applications, writing thread-safe concurrent applications becomes even more important. Concurrent Programming is a strong step towards teaching students and professionals such skills. Greg Gagne, Westminster College of Salt Lake City Salt Lake City, Utah

Exception handling in workflow management systems (WFMSs) is a very important problem since it is not possible to specify all possible outcomes and alternatives. Effective reuse of existing exception handlers can greatly help in dealing with workflow exceptions. On the other hand, cooperative support for user-driven resolution of unexpected exceptions and workflow evolution at runtime is vital for an adaptive WFMS. We have developed ADOME-WFMS via a meta-modeling approach as a comprehensive framework in which the problem of workflow exception handling can be adequately addressed. In this chapter, we present an overview of exception handling in ADOME-WFMS with procedures for supporting the following: reuse of exception handlers, thorough and automated resolution of expected exceptions, effective management of Problem Solving Agents, cooperative exception handling, user-driven computer supported resolution of unexpected exceptions, and workflow evolution.

Exception handling in a complex concurrent and distributed system (e.g. one involving cooperating rather than just competing activities) is often a necessary, but a very difficult, task. No widely accepted models or approaches exist in this area. The object-oriented paradigm, for all its structuring benefits, and real-time requirements each add further difficulties to the design and implementation of exception handling in such systems. In this paper, we develop a general structuring framework based on the coordinated atomic (CA) action concept for handling exceptions in an object-oriented distributed system, in which exceptions in both the value and the time domain are taken into account. In particular, we attempt to attack several difficult problems related to real-time system design and error recovery, including action-level timing constraints, time-triggered CA actions, and time-dependent exception handling. The proposed framework is then demonstrated and assessed using an industrial real-time application-the Production Cell III case study.

This paper shows how modern structuring techniques can be employed in integrating complex web applications such as travel agency systems. The main challenges the developers of such systems face are dealing with legacy web services and incorporating means for tolerating errors. Because of the very nature of such systems, exception handling is the main recovery technique to be applied in their development. We employ coordinated atomic actions to allow disciplined handling of such abnormal situations by recursively structuring the integrated system and by associating handlers with such actions. We use protective wrappers in such a way that each operation on legacy components is transformed into an atomic action with a well-defined interface. To accommodate a combined use of several ready-made environments (such as communication packages, services and run-time supports), we employ a multilevel exception handling. We believe that these techniques are generally applicable for both: structuring integrated web applications and providing their fault tolerance.

Component-based software systems built out of reusable software components are being used in a wide range of applications which have high dependability requirements. In order to accomplish the required levels of dependability, it is necessary to incorporate into these complex systems means for to cope with software faults. Exception handling is a well-known technique for adding forward error recovery to software systems supported by various mainstream programming languages. However, exception handling for component-based applications at the architectural level introduces new challenges which are not addressed by traditional exception handling systems, such as unavailability of source code, specially when off-the-shelf components are employed. In this paper, we present an exception handling system which adds fault tolerance to component-based systems at the architectural level. Our solution considers issues which are specific to component-based applications, such as unavailability of source code. We also present a framework which implements the proposed exception handling system for applications built using the C2 architectural style.KeywordsService RequestException HandlingArchitectural LevelDependable SoftwareClient ComponentThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

In a contract, exceptional clauses specify sanctions that come in force when the primary obligations are not fulfilled. An important aspect of exception handling is their resolution: determining which particular exception clause should be enforced when a violation is detected. This paper presents a specification and resolution technique for electronic contracts that can be used by a third party exception resolution service.

Open Multithreaded Transactions form an advanced transaction model that provides features for controlling and structuring not only accesses to objects, as usual in transaction systems, but also threads taking part in transactions. The model allows several threads to enter the same transaction in order to perform a joint activity. It provides a flexible way of manipulating threads executing inside a transaction by allowing them to be forked and terminated, but it restricts their behavior in order to guarantee correctness of transaction nesting and isolation among transactions. In addition, transactions are exception handling contexts, and the model therefore provides forward and backward error recovery. In this paper we show that the model is indeed powerful, and that a complex application, i.e. an online auction system, can be designed and implemented in a very elegant way.

Today networks are too cumbersome due to the incoherent integration of various technologies developed over time. Convergence of data, voice, and video has caused the retro-fitting of a network to support non-native traffic types and this has led to sub-par performance for every traffic type. Fundamental changes are warranted to support high bandwidth traffic. The network must guarantee end-to-end delivery and provide inherent protection within the physical structure. We propose that the main traffic types of today's applications should be carried using the following features: connection-oriented service, traffic grooming to fill those connection oriented pipes, and forward error recovery with protection provided in the physical layer. We present some of our research results.

The authors propose the concept of concurrent correspondent modules as a strategy to implement software fault tolerance. It is based on the concurrent execution of the primary, and its redundant correspondent versions. Error detection and forward error recovery are performed by the comparative test. Using Ada tasks in conjunction with the abort facility, concurrent correspondent modules are easily and efficiently implemented. The use of concurrent Ada enhances the power of concurrent correspondent modules, making this an elegant, effective and feasible alternative to other fault-tolerant approaches. >

This paper discusses some of the typical characteristics of modern Web applications and analyses some of the problems the developers of such systems have to face. One of such types of applications is integrated Web application, i.e. application that integrates several independent Web services. The paper focuses on providing software fault tolerance for such systems. The solution we put forward employs the concept of co-ordinated atomic (CA) actions for structuring such applications and for providing fault tolerance using exception handling. The paper discusses important design and implementation decisions we have made while developing a travel agency (TA) case study and attempts to generalize them to allow CA actions to be easily applied for building dependable Web applications.