Operating System Tutorial

Operating System Tutorial Types of Operating System Evolution of Operating System Functions of Operating System Operating System Properties Operating System Services Components of Operating System Needs of the Operating System

Operating Systems

Linux Operating System Unix Operating System Ubuntu Operating System Chrome Operating Systems Fedora Operating System MAC Operating System MS Windows Operating System Solaris Operating System Cooperative Operating System CorelDRAW Operating System CentOS FreeBSD Operating Systems Batch Operating System MS-DOS Operating System Commercial Mobile Operating Systems

Differences

Difference Between Multi-programming and Multitasking Difference between C-LOOK and C-SCAN Difference between Rotational Latency and Disk Assess Time Trap vs Interrupt Difference between C-SCAN and SSTF Difference between SCAN and FCFS Difference between Seek Time and Disk Access Time Difference between SSTF and LOOK Difference between Process and Program in the Operating System Difference between Protection and Security in Operating System

How To

How to implement Monitors using Semaphores How to Install a Different Operating System on a PC

Questions

What is Kernel and Types of Kernel What is DOS Operating System What is Thread and Types of Thread What is Process Scheduler and Process Queue What is Context Switching What is CPU Scheduling What is Producer-Consumer Problem What is Semaphore in Operating System Monitors in Operating System What is Deadlock What is Paging and Segmentation What is Demand Paging What is Virtual Memory What is a Long term Scheduler What is Page Replacement in Operating System What is BSR Mode What is Convoy Effect What is Job Sequencing in Operating System Why is it critical for the Scheduler to distinguish between I/O-bound and CPU-bound programs Why is there a Need for an Operating System

Misc

Process Management Process State Scheduling Algorithm FCFS (First-come-First-Serve) Scheduling SJF (Shortest Job First) Scheduling Round-Robin CPU Scheduling Priority Based Scheduling HRRN (Highest Response Ratio Next) Scheduling Process Synchronization Lock Variable Mechanism TSL Mechanism Turn Variable Mechanism Interested Variable Mechanism Deadlock Avoidance Strategies for Handling Deadlock Deadlock Prevention Deadlock Detection and Recovery Resource Allocation Graph Banker’s Algorithm in Operating System Fixed Partitioning and Dynamic Partitioning Partitioning Algorithms Disk Scheduling Algorithms FCFS and SSTF Disk Scheduling Algorithm SCAN and C-SCAN Disk Scheduling Algorithm Look and C-Look Disk Scheduling Algorithm File in Operating System File Access Methods in Operating System File Allocation Method Directory Structure in Operating System N-Step-SCAN Disk Scheduling Feedback Queue in Operating System Contiguous Memory Allocation in Operating System Real-time Operating System Starvation in Operating System Thrashing in Operating System 5 Goals of Operating System Advantages of Operating System Advantages of UNIX Operating System Bit Vector in Operating System Booting Process in Operating System Can a Computer Run Without the Operating System Dining Philosophers Problem in Operating System Free Space Management in Operating System Inter Process Communication in Operating System Swapping in Operating System Memory Management in Operating System Multiprogramming Operating System Multitasking Operating Systems Multi-user Operating Systems Non-Contiguous Memory Allocation in Operating System Page Table in Operating System Process Scheduling in Operating System Segmentation in Operating System Simple Structure in Operating System Single-User Operating System Two Phase Locking Protocol Advantages and Disadvantages of Operating System Arithmetic operations in binary number system Assemblers in the operating system Bakery Algorithm in Operating System Benefits of Ubuntu Operating System CPU Scheduling Criteria in Operating System Critical Section in Operating System Device Management in Operating System Linux Scheduler in Operating System Long Term Scheduler in Operating System Mutex in Operating System Operating System Failure Peterson's Solution in Operating System Privileged and Non-Privileged Instructions in Operating System Swapping in Operating System Types of Operating System Zombie and Orphan Process in Operating System 62-bit operating system Advantages and Disadvantages of Batch Operating System Boot Block and Bad Block in Operating System Contiguous and Non - Contiguous Memory Allocation in Operating System Control and Distribution Systems in Operations Management Control Program in Operating System Convergent Technologies in Operating System Convoy Effect in Operating System Copy Operating Systems to SSD Core Components of Operating System Core of UNIX Operating System Correct Value to return to the Operating System Corrupted Operating System Cos is Smart Card Operating System Cosmos Operating Systems Examples Generation of Operating System Hardware Solution in Operating System Process Control Block in Operating System Function of Kernel in Operating System Operating System Layers History of Debian Operating Systems Branches and Architecture of Debian Operating Systems Features and Packages of Debian Operating Systems Installation of Operating System on a New PC Organizational Structure and Development in Debian Operating Systems User Interface in Operating System Types Of Memory in OS Operating System in Nokia Multilevel Paging in OS Memory Mapping Techniques in OS Memory Layout of a Process in Operating System Hardware Protection in Operating System Functions of File Management in Operating System Core of Linux Operating System Cache Replacement Policy in Operating System Cache Line and Cache Size in Operating System What is Memory Mapping? Difference Between Network Operating System And Distributed Operating System What is the difference between a Hard link and a Soft Link? Principles of Preemptive Scheduling Process Scheduling Algorithms What is NOS? What is the Interrupt I/O Process? What is Time Sharing OS What is process termination? What is Time-Sharing Operating System

Critical Section in Operating System

What is Critical section?

In operating systems, a critical section is a section of code that is executed by multiple threads or processes and accesses shared resources, such as variables or data structures. A critical section must be executed atomically, which means that it should not be interrupted by another thread or process that also wants to access the same shared resource.

The purpose of implementing critical sections is to ensure that shared resources are accessed in a mutually exclusive manner, so that the results of each thread's or process's operations on the shared resource are consistent and correct.

To prevent race conditions, which occur when two or more threads or processes access the same shared resource simultaneously and the outcome depends on the order in which the operations are performed, operating systems use synchronization mechanisms such as semaphores and monitors to enforce mutual exclusion in critical sections.

Example of Critical Section

A common example of a critical section is a bank account that is shared among multiple threads or processes. Suppose that two threads attempt to simultaneously withdraw money from the account, and the balance is updated after each withdrawal operation. If the threads do not access the account in a mutually exclusive manner, race conditions can occur, and the resulting balance may be incorrect.

To address this problem, the code that withdraws money from the account must be executed in a critical section. In this critical section, the mutual exclusion property ensures that only one thread can access the account at a time, and the balance is updated atomically to ensure consistency and correctness.

Here is an example of a critical section that withdraws money from a bank account:

  1. Enter critical section
  2. Read the current balance of the account
  3. Withdraw the requested amount from the account
  4. Update the account balance
  5. Exit critical section

In this example, only one thread or process can execute the critical section at a time, and any other thread that attempts to enter the critical section must wait until the first thread has completed its operation and exited the critical section. By enforcing mutual exclusion and atomicity in the critical section, the bank account is protected from race conditions and ensures that the resulting balance is correct and consistent.

Characteristics of Critical Section

The characteristics of a critical section in an operating system include the following:

  • Shared Resource: The critical section involves accessing a shared resource that is shared among multiple threads or processes.
  • Mutual Exclusion: Only one thread or process can access the shared resource in a critical section at any given time to prevent race conditions and ensure correctness of operations.
  • No pre-emption: Once a thread or process enters a critical section, it cannot be pre-empted or interrupted by another thread or process until it exits the critical section. This ensures that the thread or process can complete its operations on the shared resource in a mutually exclusive manner.
  • Finite Execution Time: A critical section must execute in a finite amount of time to avoid causing delays in other processes or threads that are waiting to access the shared resource.
  • Blocking: If a thread or process is unable to enter a critical section due to the presence of another thread or process that is currently accessing the shared resource, it must block or wait until it can enter the critical section.
  • Atomicity: Operations performed within the critical section must be performed atomically, meaning that they must execute as a single, indivisible operation. This ensures that the shared resource is left in a consistent state after each operation, regardless of any race conditions that may arise.

Solution of critical section problems

There are several solutions to the critical section problem in operating systems, which ensure that only one thread or process can access a shared resource at any given time. Some of the commonly used solutions are:

  • Locks:One of the most popular solutions to the critical section problem is the use of locks, such as mutexes and semaphores, which are synchronization mechanisms that allow threads or processes to acquire exclusive access to a shared resource. A thread or process that wants to enter the critical section acquires the lock and releases it when it exits the critical section.
  • Atomic Operations: Atomic operations are operations that execute as a single, indivisible unit, and cannot be interrupted by other threads or processes. By using atomic operations for operations within the critical section, the mutual exclusion property is automatically enforced.
  • Monitors: Monitors are higher-level synchronization constructs that encapsulate data and procedures into a single module. Monitors provide mechanisms to enter and exit the critical section and ensure that only one thread or process can access the shared resource at any given time.
  • Peterson's Algorithm: Peterson's algorithm is a classical solution to the critical section problem that uses two shared variables to enforce mutual exclusion. The algorithm allows each thread to enter its critical section while preventing other threads from entering their critical section at the same time.
  • Test-and-Set Instruction: The test-and-set instruction is a hardware instruction that can be used to implement mutual exclusion. The instruction reads a memory location and sets it to a specified value in a single atomic operation. By using the test-and-set instruction, threads or processes can acquire and release locks in a mutually exclusive manner.