Inside Macintosh: Processes

Chapter 6 - Deferred Task Manager

This chapter describes how your application or device driver can use the Deferred Task Manager to defer the execution of lengthy tasks until interrupts are reenabled. Time-consuming tasks, if executed at interrupt time, can prevent the execution of interrupt tasks having the same or lower priority. The Deferred Task Manager allows you to improve interrupt handling by deferring a task until all other interrupts have been serviced.

Lengthy tasks are often initiated by slot cards. As a result, you probably need to read the information in this chapter only if your application or driver deals with slot-card interrupts. However, you can use the services provided by the Deferred Task Manager whenever you need to install a lengthy interrupt task capable of running with all interrupts enabled. You can, for example, defer the execution of completion routines, Time Manager routines, and VBL tasks.

To use this chapter, you should be familiar with interrupts and interrupt tasks in general. See the chapter "Introduction to Processes and Tasks" in this book for an overview of both interrupt and noninterrupt processing. Because the Deferred Task Manager maintains all deferred tasks in a queue until their execution, you should also be familiar with operating-system queues, as described in the chapter "Queue Utilities" in Inside Macintosh: Operating System Utilities.

This chapter begins with a description of interrupt priority levels and explains when you might need to use the Deferred Task Manager. Then it shows how you can use the Deferred Task Manager to defer a task. The chapter concludes with a description of the Deferred Task Manager's data structure and routine.

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Chapter Contents

About the Deferred Task Manager

Using the Deferred Task Manager

Checking for the Deferred Task Manager

Installing a Deferred Task

Defining a Deferred Task

Deferring a Slot-Based VBL Task

Deferred Task Manager Reference

Data Structure

Deferred Task Manager Routine

Application-Defined Routine

Deferred Tasks

Summary of the Deferred Task Manager

Pascal Summary

Data Type

Deferred Task Manager Routine

Application-Defined Routine

C Summary

Data Type

Deferred Task Manager Routine

Application-Defined Routine

Assembly-Language Summary

Deferred Task Manager Queue Element

Global Variables

Result Codes