Scheduling and Context Switching in XINU

Introduction

This section describes how XINU manages processes in terms of context switching and process scheduling.

First - there are a few things you have to remember:

• A context switch happens when one processes loses control of the CPU (stops executing) and another starts.
• In order to perform a context switch, several things must happen:
• First, enough information about the currently running process must be saved so that it may later be restarted from exactly where it left off.
• Second, the next process to be run must be selected. This is part of Process Scheduling (the parts of process scheduling that make up this task are the priority function and arbitration rule).
• Finally, the chosen process must be started (this is called dispatching the process).
• In many operating systems (as in XINU) process priorities are assigned by the creator of the process (externally assigned priorities).