ABSTRACT   Understanding multithreading and its impact on software development is a demanding task. This lecture discusses the design of object-oriented, concurrent applications using multiple threads, and the implementation of such applications in C++ and Java. Naturally, a 3-hours presentation cannot cover all aspects relevant to multithreading. The talk instead focuses on one particularly important aspect: concurrency control techniques, among them mutual exclusion, guarded suspension, and more advanced techniques such as reader/writer synchronization. In order to implement these patterns in C++ or Java, one needs to know which concurrency control instruments are supported in each of the languages. Along with an introduction to the respective features in C++ and Java, strengths and weaknesses in both languages are discussed.  Not covered in this talk are thread activities and cooperative interaction e.g. starting threads, thread completion, termination policies. Also omitted are differences between thread APIs, as well as thread scheduling and priorities. These aspects are subject of a full-day seminar. Access to shared resources. In multithreaded environments concurrently running components often share resources. Concurrent access to shared resources can corrupt the resource or put it into an inconsistent state if access for modification of the resource through two concurrent threads is interleaved. For this reason, one of the most urgent problem to be tackled in multithreaded programming is control of access to shared resources and, in particular, to shared data. The talk explains which data is shared, explicitly or implicitly, in C++ and Java, and suggests programming techniques for concurrency control in both languages. One of the suggested techniques is classification of access methods using the conflict set method.  Concurrency Control Techniques. In order to control the access to shared data, multithreaded environments support concurrency control instruments like mutex and condition variable. The talk explains how these instruments can be used and discusses three typical control patterns and their implementation in object-oriented languages such as C++ and Java: monitor, guarded suspension, and reader/writer. Tips and tricks are provided for improving the design of a concurrent program. Performance tuning is suggested by avoiding useless notifications or unnecessary waiting or polling. Also, typical pitfalls are mentioned: the notorious nested monitor problem is explained.  Implementation Aspects. The third part of the talk is devoted to implementation aspects such as programming techniques for turning existing classes into thread-safe classes or designing new classes especially for use in multithreaded systems. The decomposition into concurrency control and ground functionality is proposed and a discussion of combining both, via inheritance or delegation, completes the talk.

Level:	intermediate
Duration:	1.5-3.0 hours
Prerequisites:	working knowledge of C++ or Java;   familiarity with concurrency control not required
Presented at:	Software Development , Washington DC, September 1997  Object World , Frankfurt, October 1997 C++ World , San Jose CA, November 1997 Object Expo France , Paris, November 1997 C++ World / OOP, Munich, February 1998 (presented by Klaus Kreft)  Software Development , San Francisco CA, February 1998