Covariance, contravariance, and synchronization constraints (1996) [1 citations — 1 self]
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Abstract:
Abstract: Object Orientation and concurrent progamming are a natural match. Objects correspond to processes in a concurrent program; a message from one object to another invoking a method of the latter, corresponds naturally to (message passing) interaction between processes in a concurrent program. Despite this close correspondence, progress in developing an OO approach to concurrency has been limited. One important problem has been the so-called inheritance anomaly which is concerned with how and how easily synchronization constraints specified in a base class may be modified in a derived class. Our concern in the current paper is more basic. We address the question of what types of modifications in the synchronization constraints inherited from the base class ought to be permitted to be made in the derived class. We identify the modifications that are reasonable, especially when the problem is viewed from the point of view of a client of the class. We point out that when viewed from this perspective, some of the current proposals for expressing synchronization constraints allow precisely the wrong types of modifications to be made in the derived classes. We also analyze the relation between this question and the problems that inheritance encounters already in the sequential case, such as the covariance versus contravariance conflict. 1
Citations
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