Transaction Support for Ada

This paper describes the transaction support framework OPTIMA and its implementation for Ada 95. First, a transaction model that fits concurrent programming languages is presented. Then the design of the framework is given. Applications from many different domains can benefit from using transactions; it is therefore important to provide means to customize the framework depending on the application requirements. This flexibility is achieved by using design patterns. Class hierarchies with classes implementing standard transactional behavior are provided, but a programmer is free to extend the hierarchies by implementing application-specific functionalities. An interface for Ada programmers is presented and its use demonstrated via a simple example

Object-Oriented Stable Storage

This report is the result of a diploma thesis of Xavier Caron, a computer science student at the Software Engineering Lab (LGL), which is part of the Swiss Federal Institute of Technology in Lausanne (EPFL). The LGL is currently developing an object-oriented library providing transaction support for Ada programmers. Transactions are actions that have the well-known ACID properties (Atomicity, Consistency, Isolation, and Durability). Durability of objects can be achieved by saving their state to so-called "stable storage". The goal of this project is to implement the two following forms of stable storage: 1) Stable storage using a technique called mirroring. The integrity of the stored data must be guaranteed even in the presence of crash failures. 2) Stable storage based on replication. Using the distributed programming facilities of Ada 95, a mechanism must be devised that allows to broadcast the information that has to be made durable to a group of collaborating machines for storage. Of course, it should also be possible to retrieve the data in a consistent manner. This report describes the system design and implementation in Ada 95

Concurrency Control for Transactional Drago

The granularity of concurrency control has a big impact on the performance of transactional systems. Concurrency control granu- larity and data granularity (data size) are usually the same. The e ect of this coupling is that if a coarse granularity is used, the overhead of data access (number of disk accesses) is reduced, but also the degree of concurrency. On the other hand, if a ne granularity is chosen to achieve a higher degree of concurrency (there are less con icts), the cost of data access is increased (each data item is accessed independently, which increases the number of disk accesses). There have been some pro- posals where data can be dynamically clustered/unclustered to increase either concurrency or data access depending on the application usage of data. However, concurrency control and data granularity remain tightly coupled. In Transactional Drago, a programming language for building distributed transactional applications, concurrency control has been un- coupled from data granularity, thus allowing to increase the degree of concurrency without degrading data access. This paper describes this approach and its implementation in Ada 95

Implementing Exceptions in Open Multithreaded Transactions Based On Ada 95 Exceptions

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Combining Tasking and Transactions, Part II: Open Multithreaded Transactions

This position paper is a follow-up paper of the one presented at the last IRTAW workshop. The paper describes a model for providing transaction support for concurrent programming languages such as Ada 95. In order to achieve smooth integration, the use of the concurrency features provided by the Ada language should not be restricted inside a transaction. A transaction model that meets this requirement is presented. Tasks inside such a transaction may spawn new tasks, but also external tasks are allowed to join an ongoing transaction. A blocking commit protocol ensures that no task leaves the transaction before its outcome has been determined. Exceptions are used to inform all participants in case a transaction aborts. The design of a library that provides support for the transaction model is presented, and possible interfaces for the Ada programmer are discussed

Auction System Design Using Open Multithreaded Transactions

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

Open Multithreaded Transactions: Keeping Threads and Exceptions under Control

Although transactional models have proved to be very useful for numerous applications, the development of new models to reflect the ever-increasing complexity and diversity of modern applications is a very active area of research. Analysis of the existing models of multithreaded transactions shows that they either give too much freedom to threads and do not control their participation in transactions, or unnecessarily restrict the computational model by assuming that only one thread can enter a transaction. Another important issue, which many models do not address properly, is providing adequate exception handling features. In this paper a new model of multithreaded transactions is proposed. Its detailed description is given, including rules of thread behaviour when transactions start, commit and abort, and rules of exception raising, propagation and handling. This model is supported by enhanced error detection techniques to allow for earlier error detection and for localised recovery. General approaches to implementing transaction support are discussed and a detailed description of an Ada implementation is given. Special attention is paid to outlining typical applications for which this model is suitable and to comparing it with several known approaches (Coordinated Atomic actions, CORBA, and Argus)

Open Multithreaded Transactions: A Transaction Model for Concurrent Object-Oriented Programming

To read the abstract, please go to my PhD home page

Transaction Support for Ada

This paper describes the transaction support framework OPTIMA and its implementation for Ada 95. First, a transaction model that fits concurrent programming languages is presented. Then the design of the framework is given. Applications from many different domains can benefit from using transactions; it is therefore important to provide means to customize the framework depending on the application requirements. This flexibility is achieved by using design patterns. Class hierarchies with classes implementing standard transactional behavior are provided, but a programmer is free to extend the hierarchies by implementing application-specific functionalities. An interface for Ada programmer