Build A
Portable Multitasking Environment
in ``C''
——————————— #1 – Switching Contexts

This is the first in a series of three construction articles in which you build a portable multitasking environment for programming. The purpose of the series is two-fold:

1. To Explain the programming concepts and constructs which come into play when building, programming, and operating within a multitasking environment.

2. To Construct a general-purpose multitasking environment for programming which is portable to most stack-based languages and to most most mini, micro, and mainframe computers (so your multitasking programs will be portable).

The ``task'' is divided up into three construction articles, each of which builds upon the code and concepts of the previous one but is complete in itself (it does not depend on the successive articles). The three articles are:

#1

Switching Contexts

#2

Organizing a Task Force

#3

Managing Resources

This article is the first in the series. It explains the concept of context switching and constructs a general-purpose and portable context switch...

• Contents
• What's a Context Switch?
  • The No-Return / Multiple-Return Approach
  • The Switch Function Approach
  
  
• Building a Context Switch in ``C''
  • The Thread Cluster - Data Structure
  • The Thread Cluster - Code Structure
    • Achieving Atomicity with Signals and Semaphores
    • Switching Between Contexts: mpthd
  • Creating and Destroying Contexts: mpthd and mpthd
  
  
• Putting the Context Switch to Good Use
  • Software-Driven Switching Interprocess Communication
  • Hardware-Driven Switching Resource Management
  
  
• Conclusions