Principles of Secure Operating Systems: Processes & IPC

Strict Alternation Technique

Processes alternate access to critical regions.

Shared Memory

Memory accessible by multiple processes.

Scheduler

Manages process execution and switching.

Entry Section

Code for requesting access to critical region.

Exit Section

Code for releasing access from critical region.

Remainder Section

Code executed outside critical region.

Hardware Solutions to race conditions

Techniques like disabling interrupts for mutual exclusion.

what happens when you Disable Interrupts

Prevents context switching during critical region access.

Semaphore

Synchronization primitive for controlling access to resources.

Non-critical Section

Code that does not access shared resources.

Shared Storage

Memory area used by multiple processes.

Blocking in ICP

Preventing process execution until a condition is met.

Waiting Forever in terms of processes

Condition where a process cannot enter critical region.

Process Execution

Running of a process by the CPU.

What does User Process Control do or not do?

User processes shouldn't disable interrupts.

Multiprocessor Issues

Disabling interrupts affects only one CPU.

Strict Alternation

Processes alternate access to critical region.

Critical Region (CR)

Section of code accessing shared resources.

Enter-Region Call

Process waits to enter the critical region.

Leave-Region Call

Process signals exit from the critical region.

Non-Critical Section (non-CR)

Code section not accessing shared resources.

Process Blocking

One process waiting due to another's state.

Turn Initialization

Initially set to 0 for strict alternation.

Process Coordination

Managing access to shared resources among processes.

Race Condition

Situation where processes compete for resources.

Concurrency

Multiple processes executing simultaneously.

Shared Memory Access

Processes reading/writing to common memory space.

What is Peterson's solution?

A software-based approach that ensures mutual exclusion between two processes.

What does Peterson's solution allow processes to do?

Safely access a critical region.

Mutual Exclusion

Prevention of simultaneous access to critical regions.

Critical Region

Section of code requiring exclusive access.

Busy Waiting

Process waits in a loop for a condition.

Turn Variable

Indicates whose turn it is to enter critical region.

Rule 1 for solution to race conditions

No two processes in critical regions simultaneously.

Rule 3 solution to race conditions

Non-critical processes cannot block others.

Rule 4 solution to race conditions

No process should wait indefinitely for access.

Thread Synchronization

Coordination of threads to prevent resource conflicts.

What does Spinlock do in Petersons solution ?

Busy waiting lock that wastes CPU time.

Rule 2 for solution to race conditions

No assumptions may be made about speeds or the number of CPUs