The critical section is a term used in the field of operating systems to describe a portion of code that accesses a shared resource. The critical section is considered to be a critical area because it can cause problems if two or more processes attempt to access the shared resource simultaneously. To prevent these problems, the critical section must be synchronized, or protected, so that only one process can access the shared resource at a time.
There are several synchronization mechanisms that can be used to protect the critical section, including semaphores, monitors, and mutexes. Each of these mechanisms provides a way for processes to coordinate their access to the shared resource, and to ensure that the critical section is executed in a safe and predictable manner.
Semaphores: A semaphore is a data structure that is used to control access to a shared resource. It acts as a gatekeeper, allowing only one process to access the resource at a time. The semaphore keeps track of the number of available resources, and if a process requests a resource that is not available, the process will be blocked until the resource becomes available. Semaphores are used to control access to resources, prevent race conditions, and ensure that processes are executed in a predictable order.
For example, consider a system that has two processes, P1 and P2, that both need to access a shared resource, R. To prevent race conditions, a semaphore could be used to control access to the resource. P1 and P2 would both request access to the semaphore, and the semaphore would ensure that only one process accesses the resource at a time. If P1 acquires the resource, P2 would be blocked until P1 releases the resource.
Monitors: A monitor is a higher-level synchronization mechanism that provides a way for processes to coordinate their access to shared resources. Monitors provide a set of synchronization primitives, such as wait and signal, that allow processes to coordinate their access to shared resources. Monitors also provide a way for processes to block until a specific condition is met, such as the availability of a resource.
For example, consider a system that has two processes, P1 and P2, that both need to access a shared resource, R. To prevent race conditions, a monitor could be used to control access to the resource. P1 and P2 would both request access to the monitor, and the monitor would ensure that only one process accesses the resource at a time. The monitor would also provide a set of synchronization primitives, such as wait and signal, that would allow processes to coordinate their access to the resource.
Mutexes: A mutex (short for “mutual exclusion”) is a type of semaphore that is specifically designed for controlling access to a single resource. Like a semaphore, a mutex is used to coordinate access to a shared resource, but it allows only one process to access the resource at a time. If a process requests access to a resource that is already being accessed by another process, the process will be blocked until the resource becomes available.
For example, consider a system that has two processes, P1 and P2, that both need to access a shared resource, R. To prevent race conditions, a mutex could be used to control access to the resource. P1 and P2 would both request access to the mutex, and the mutex would ensure that only one process accesses the resource at a time. If P1 acquires the resource, P2 would be blocked until P1 releases the resource.
In conclusion, the critical section is a crucial aspect of synchronization in operating systems, as it defines the portion of code that accesses a shared resource and is considered to be critical because it can cause problems if two or more processes attempt to access the shared resource simultaneously. By using synchronization mechanisms such as semaphores, monitors, and mutexes, operating systems can protect the critical section and ensure that the shared resource is accessed in a safe and predictable manner.
For example, in a banking system, a shared resource could be a bank account, and the critical section could be the code that updates the account balance. To ensure that the account balance is updated correctly, the critical section must be protected so that only one process can access the account at a time. Using a synchronization mechanism, such as a mutex, the operating system can ensure that the critical section is executed in a safe and predictable manner, and that the account balance is updated correctly.
In general, the critical section is an important aspect of operating systems, as it provides a way for processes to coordinate their access to shared resources, and to ensure that the resources are used in a safe and efficient manner. By using synchronization mechanisms to protect the critical section, operating systems can provide robust and predictable access to shared resources, and can ensure that multiple processes work together in a coordinated manner.
