Summary

This chapter has introduced the concept of interleaving both as a way of executing multiple processes on a single processor and as a way of modeling concurrent execution. The chapter has dealt mainly with modeling concurrency:

• The model of concurrency is interleaved and asynchronous. By asynchronous we mean that processes proceed at arbitrary relative speeds and consequently their actions can be arbitrarily interleaved.

• The parallel composition of two or more processes modeled as finite state processes results in a finite state process that can generate all possible interleavings of the execution traces of the constituent processes.

• Process interaction is modeled by shared actions, where a shared action is executed at the same time by all the processes that share the action. A shared action can only occur when all the processes that have the action in their alphabets are ready to participate in it – they must all have the action as an eligible choice.

• Process labeling, relabeling and hiding are all ways of describing and controlling the actions shared between processes. Minimization can be used to help reduce the complexity of systems with hidden actions.

• Parallel composition and the labeling operator describe the static structure of a model. This structure can be represented diagrammatically by structure diagrams.

• Concurrent execution in Java is programmed simply by creating and starting multiple threads.