The Process

• What is a process?
• Multitasking
• How does the OS track processes
• Context switching and Scheduling
• Process API

What’s a process

A program in execution

Multitasking

• Modern OSes run dozens to hundreds of processes simultaneously
• Could exceed the hardware capacity

CPU Memory Virtualization

• Time-slicing of CPU(s) is done to simulate concurrency
• Memory is partitioned as well
• Per-process view is a uniform address space
• Lazy/On-demand loading of processes lowers total burden

Contrast that to batch processing where jobs were done individually and synchronously. Cringe.

Forms of Multitasking

• Cooperative multitasking: processes voluntarily give control to the OS
• Preemptive multitasking: OS policies transitions (how?)
• Real-time systems: hard, fixed time constraints

01/29/2021

Scheduler

• Composed of policies (high level) and mechanisms (low level) to select which process is allocated resources.

Unix Process API

• Manage processes
• Create processes
• Synchronization
• Communication

The Unix process API consists of flexible and orthogonal (meaning they are disparate so they are composable) system calls.

• Creation: fork
• Program execution: exec
• Synchronization: wait
• Termination: exit