14 - Detailed Real-Time Software Design

Summary

After structuring the system into tasks (in Chapter 13), this chapter describes the detailed software design. In this step, the internals of composite tasks that contain nested objects are designed, detailed synchronization issues of tasks accessing passive classes are addressed, connector classes are designed that encapsulate the details of inter-task communication, and each task's internal event sequencing logic is defined. Several examples are given in Pseudocode of the detailed design of task synchronization mechanisms, connector classes for inter-task communication, and task event sequencing logic.

The detailed software design is depicted on a detailed concurrent communication diagram, which adds more detail to the concurrent communication diagram developed during task structuring. It depicts the internal design of clustered tasks and the design of connector objects.

Section 14.1 describes the design of composite tasks, including the internal design of temporal and control clustering tasks. Section 14.2 describes the synchronization of access to classes using different synchronization mechanisms, including the mutual exclusion algorithm and the multiple readers and writers algorithm. Section 14.3 describes the synchronization of access to passive objects using the monitor concept. Section 14.4 describes the design of connectors for inter-task communication, in particular for synchronous and asynchronous message communication. Section 14.5 describes the detailed software design of tasks using task behavior specifications and event sequencing logic. Section 14.6 provides detailed software design examples of task communication and synchronization in real-time robot and vision systems. Finally, Section 14.7 briefly describes implementing concurrent tasks in Java using threads.

DESIGN OF COMPOSITE TASKS

A composite task is a task that encapsulates one or more nested objects. This section describes the detailed design of composite tasks, which includes tasks that were structured using the task clustering criteria. Such tasks are designed as composite active classes that contain nested passive classes. In a real-time design, typical nested classes are entity classes, input/output classes, and state machine classes.

After considering the relationship between tasks and classes, this section describes situations where it is useful to divide the responsibility between tasks and classes. Next, the design of two composite tasks is described in detail: a temporal clustering task and a control clustering task.