Capsules: a shared memory access mechanism for Concurrent C/C++

Concurrent C/C++ is a superset of C and C++ that provides parallel programming facilities based on message passing. Upon porting Concurrent C/C++to a shared memory multiprocessor, the authors believed it would be appropriate to supplement Concurrent C/C++ with explicit facilities for synchronizing accesses to shared data structures. The capsule, which is a shared memory access mechanism designed especially for Concurrent C/C++ to match the C++data abstraction facility called the class, is discussed. Capsules are like monitors but they have significant advantages. Capsules satisfy T. Bloom´s (1979) criteria for expressiveness of synchronization conditions, support inheritance, allow operations to execute in parallel, and permit them to time out. The design of capsules is reviewed. The author evaluates existing shared memory mechanisms, describes capsules, gives examples of capsules, compares capsules with monitors, and discusses how capsules are implemented by the Concurrent C compiler