Critical-Section Problem

Process Structure

• Each process has a general structure of code as such:

  

• Entry section requests permission for the process to enter its critical section

• Critical section is where the process accesses/updates shared data (data that is shared with other processes

  • When one process is executing in its critical section, no other process is allowed to execute in its critical section.

A Solution to the Critical-Race Problem

A solution to the critical-race problem must satisfy three requirements:

1. Mutual exclusion — if a process is executing in its critical section, then no other processes can be executing in their critical sections.
2. Progress —

Handling Critical Sections

Two general approaches: preemptive vs nonpreemptive kernels:

• Preemptive
• Nonpreemptive

Peterson’s Solution

Hardware-Based Solutions

Memory Barriers

Hardware Instructions

Atomic Variables

Mutex Locks