Asynchronous transfer of control in Ada 9X

Abstract

The Taft proposal is described in detail. It involves introducing a new "and" clause into the select statement thereby providing a means of programming asynchronous transfer of control without the use of the abort facility. An evaluation of the proposal considers some of its limitations, the major one of which is the possibility of deadlock if a group of tasks use the facility to affect each other. Ways of removing this difficulty are considered. The model is then compared with the alternative of introducing asynchronous exceptions. Finally a unified model is presented that combines the advantages of the Taft proposal and asynchronous exceptions.