Qualifying Types with Bracket Methods in Timor.

Abstract

A new kind of type is described whose objects ("qualifiers") have bracket methods which can modify the run-time behaviour of other objects ("targets"). Bracket methods can qualify either specific methods of a target or can separately qualify their reader and writer methods, thus allowing general qualifiers to be developed for standard activities such as synchronisation, monitoring and protection. Qualifiers are associated with a target when it is created, in the form of a qualifier list. Individual qualifiers can be dynamically added to and removed from the list even while the target object is active.

Support for Object Oriented Transactions in Timor.

“…In this sense the body statement of Timor, when used in isolation -as in earlier papers on qualifying types and bracket methods (e.g. [4,5]) -can be viewed as a convenient short form for target.body(...).…”

“…Several cases of enhancing functionality in this sense have already been described in earlier papers [4,5], including the addition of synchronisation, monitoring and protection to objects. In this paper we present more advanced features of Timor that make it possible to develop components which for example can (a) allow copies of objects to be automatically created and updated in parallel with the original objects in a system, and (b) allow an existing system to be transformed into a transaction processing system in the traditional database sense.…”

“…We assume that an application system which is to be enhanced by the transaction components presented in this section consists of a number of Timor objects (which can have different types) that can be visited by processes/threads which make method calls on the objects. If the system to be enhanced is already a concurrent one, we assume further that its previous synchronisation requirements were satisfied by the use of dynamic synchronising qualifiers along the lines described in [4], and that when the system is transformed into a transaction system these are removed from the objects which they qualify by deleting them from the qualifier lists of target objects (as described in [5]). The transaction components which we now present can thus take over the responsibility for synchronisation (as part of their function of achieving atomicity, consistency and isolation) without side effects occurring from an earlier synchronisation strategy.…”

“…modifications to the replica database. In principle this is easily achieved using Timor qualifiers (qualifying objects) with call-in bracket methods [5].…”

“…neither at the programming language source code level nor in terms of the intermediate or machine code produced by the compiler), assuming that the original application system was written in Timor. A knowledge of the basic paper on qualifying types [5] is assumed in the rest of this paper.…”