Guidelines for Multithreaded Interfaces

      By a multithreaded interface we mean one usable by multithreaded clients. Good interface design is a challenging art, and has a whole literature of its own (for example, see Parnas [11] and Lampson [9]). We have not found designing multithreaded interfaces to be very much more difficult than designing single-threaded ones. In one respect it is harder: care must be taken that serializing access to shared mutable state defined by the interface does not restrict the usefulness of that interface. In another respect it is easier: a multithreaded interface can avoid the various ad hoc techniques used when a single-threaded interface must deal with concurrency inherent in the application. Threads provide a convenient framework for designing solutions to the problem of cancelling undesired computations.