WoTUG-20

Fortunately, it is possible to introduce the CSP model into Java through sets of classes implemented on top of its monitor support. By restricting interaction between active Java objects to CSP synchronisation primitives, Java thread semantics become compositional and systems with arbitrary levels of complexity become possible. Multi-threaded Web applets and distributed applications become simpler to design and implement, race hazards never occur, difficulties such as starvation, deadlock and livelock are easier to confront and overcome, and performance is no worse than that obtained from directly using the raw monitor primitives.

The advantages of teaching parallelism in Java purely through the CSP class libraries will be discussed. (These libraries were developed jointly at Kent and Oxford Universities in the U.K. and the University of Twente in the Netherlands.)

Channels are very close to the scheduler, in fact they may be part of the scheduler. Using channels allows scheduling on communication within the program and without any explicit command from the programmer. Scheduling based on communication results in a very fast non-pre-emptive scheduling algorithm that is faster than pre-emptive scheduling to ensure fair scheduling. The program will get better real-time characteristics and the scheduler of the Java Virtual Machine can be tuned for better performance for embedded systems.

Composition constructs provide a more easy way to build robust and better-structured concurrent programs. In chapter 2 the channel interface is described and in chapter 4 the use of the channel is described by three composition (communication) constructs: (1) the sequential communication construct, (2) the parallel communication construct, and (3) the alternative communication constructs. Chapter 5 describes several examples in terms of building blocks that illustrate the use of channels and composition constructs and by which simple concurrent programs can be built.