Concurrency Annotations and Reusability Klaus-Peter Lo..hr

Widespread acceptance of concurrent object-oriented programming in the field can only be expected if smooth integration with sequential programming is achieved. This means that a common language base has to be used, where the concurrent syntax differs as little as possible from the sequential one but is associated with a "natural " concurrent semantics that makes library support for concurrency superfluous. In addition, not only should sequential classes be reusable in a concurrent context, but concurrent classes should also be reusable in a sequential context. It is suggested that concurrency annotations be inserted into otherwise sequential code. They are ignored by a sequential compiler, but a compiler for the extended concurrent language will recognize them and generate the appropriate concurrent code. The concurrent version of the language supports active and concurrent objects and favours a declarative approach to synchronization and locking which solves typical concurrency problems in an easier and more readable way than previous ap-proaches. Concurrency annotations are introduced using Eiffel as the sequential base. Key words Concurrent object-oriented programming, reusable concurrent code, concurrency annotations, Eiffel, CEiffe