📕 Process Synchronization in Operating Systems
Process synchronization is a critical aspect of operating systems that deals with coordinating the execution of multiple processes to ensure that they do not interfere with each other. In this tutorial, we will discuss the basics of process synchronization, including how it works, the critical section problem, and solutions to it.
📕 How Process Synchronization in OS Works?
In a multi-process environment, each process has its own execution sequence, and their execution may overlap or conflict with each other. Process synchronization aims to ensure that processes execute without interference and that resources are used efficiently. In order to achieve this, processes must communicate with each other and coordinate their execution.
One common technique used in process synchronization is the use of locks or semaphores. These tools are used to prevent multiple processes from accessing the same resource simultaneously, ensuring that each process obtains exclusive access to the resource when it needs it.
📕 Race Condition
A race condition occurs when multiple processes try to access and manipulate shared resources simultaneously. This can lead to unpredictable behavior and data corruption, as the order in which processes access the resource is not guaranteed.
For example, suppose two processes try to update the same variable simultaneously. The value of the variable may not be consistent, as each process may overwrite the changes made by the other process.
📕 What is the Critical Section Problem?
The critical section problem is a problem that arises when multiple processes try to access a shared resource simultaneously. The critical section is the part of the code where the shared resource is accessed and modified. The problem occurs when two or more processes try to access the critical section simultaneously, leading to race conditions and inconsistent data.
📕 Requirements of Synchronization
In operating systems, synchronization refers to the coordination of the execution of multiple processes to ensure that they do not interfere with each other. In order to achieve this coordination, there are three primary requirements that must be met: mutual exclusion, progress, and bounded waiting.
âš¡ Mutual Exclusion
Mutual exclusion refers to the requirement that only one process can access a shared resource at any given time. This means that if one process is currently accessing the resource, all other processes must wait until the resource becomes available.
To enforce mutual exclusion, operating systems typically use locks or semaphores. These tools are used to prevent multiple processes from accessing the same resource simultaneously, ensuring that each process obtains exclusive access to the resource when it needs it.
âš¡ Progress
The progress requirement ensures that if no process is currently executing in the critical section (i.e., the section of code where the shared resource is accessed and modified) and a process wants to access it, it should not be kept waiting indefinitely.
This requirement is typically achieved by using a queue to manage the order in which processes access the critical section. When a process requests access to the critical section, it is added to the queue, and the process currently executing in the critical section must release the resource before the next process in the queue can access it.
âš¡ Bounded Waiting
The bounded waiting requirement ensures that a process should not have to wait indefinitely to access the critical section. This means that there must be a limit to the amount of time that a process can be kept waiting to access a shared resource.
To enforce bounded waiting, operating systems typically use fairness algorithms that ensure that no process is starved of resources for an extended period of time. For example, the operating system may use a priority system that gives higher priority to processes that have been waiting for a long time.
📕 Solutions To The Critical Section Problem
The critical section problem is a classic synchronization problem in computer science that arises when multiple processes or threads share a common resource and need to access it simultaneously. The problem is to design a mechanism that allows only one process to access the shared resource at a time, while ensuring that the other processes wait their turn and do not interfere with each other. There are several solutions to the critical section problem, which we will discuss in detail below.
âš¡ Solution 1: Using Locks
One of the simplest and most commonly used solutions to the critical section problem is to use locks. A lock is a synchronization mechanism that allows only one process to access a shared resource at a time. When a process wants to access the critical section, it must first acquire the lock. If the lock is already held by another process, the requesting process is blocked and put on a wait queue until the lock becomes available.
Once a process has finished accessing the critical section, it releases the lock, allowing the next process in the wait queue to acquire it and access the critical section. This ensures that only one process can access the shared resource at a time and that the other processes wait their turn.
âš¡ Solution 2: Using Semaphores
Another solution to the critical section problem is to use semaphores. A semaphore is a synchronization mechanism that allows multiple processes to access a shared resource at the same time, but only up to a certain limit.
A binary semaphore, also known as a mutex, is a special type of semaphore that is used to enforce mutual exclusion. When a process wants to access the critical section, it must first acquire the mutex. If the mutex is already held by another process, the requesting process is blocked and put on a wait queue until the mutex becomes available.
Once a process has finished accessing the critical section, it releases the mutex, allowing the next process in the wait queue to acquire it and access the critical section. This ensures that only one process can access the shared resource at a time and that the other processes wait their turn.
âš¡ Solution 3: Using Monitors
A monitor is a higher-level synchronization mechanism that provides a way to encapsulate critical sections and synchronize access to shared resources. In a monitor, all shared data and methods are contained within a single module or object, which can be accessed only by acquiring a lock on the monitor.
When a process wants to access the shared resource, it first acquires the lock on the monitor, which ensures mutual exclusion. Once the lock is acquired, the process can access the shared data and methods within the monitor.
Monitors also provide a way to implement condition variables, which allow processes to wait for a specific condition to occur before continuing. For example, a process may wait for a certain value to be set before continuing.
âš¡ Solution 4: Using Atomic Operations
An atomic operation is an operation that is guaranteed to be executed as a single, indivisible step. Atomic operations are typically provided by the hardware or operating system, and they can be used to implement synchronization mechanisms.
For example, the compare-and-swap (CAS) operation is an atomic operation that is commonly used to implement locks and other synchronization mechanisms. The CAS operation allows a process to atomically compare the current value of a variable with a desired value, and if they are equal, to set the variable to a new value.
Using CAS, a process can attempt to acquire a lock by setting a variable to a specific value. If the variable is already set to that value, the process has successfully acquired the lock. If the variable is not set to that value, the process retries until it successfully acquires the lock.
In conclusion, the critical section problem can be solved using various synchronization mechanisms such as locks, semaphores, monitors, and atomic operations. Each of these solutions ensures mutual exclusion
Thanks for reading, and happy coding!
Understanding Process Management in Operating Systems -> Mutex and Producer-Consumer Problem: Synchronization Techniques in Operating Systems