In operating systems, a critical section refers to a segment of code that is executed by multiple concurrent threads or processes, and which accesses shared resources. These shared resources may include variables, data structures, CPUs, or any I/O device. The critical section cannot be executed by more than one process at the same time, and the operating system faces difficulties in allowing and disallowing processes from entering the critical section. The critical section problem is used to design a set of protocols that can ensure that the race condition among the processes will never arise.
A critical section typically consists of two parts: the entry section and the exit section. The entry section handles the entry into the critical section, acquires the resources needed for execution by the process, and ensures mutual exclusion. The exit section handles the exit from the critical section, releases the resources, and informs the other processes that the critical section is free.
To synchronize the cooperative processes, a solution to the critical section problem must provide mutual exclusion, progress, and bounded waiting. Mutual exclusion means that only one process can be inside the critical section at any time, and if any other processes require the critical section, they must wait until it is free. Progress means that if a process is not using the critical section, then it should not stop any other process from accessing it. Bounded waiting means that each process must have a limited waiting time and should not wait endlessly to access the critical section.
Some software-based solutions for the critical section problem include Petersons solution, semaphores, and monitors. Some hardware-based solutions involve atomic instructions such as TestAndSet, compare and swap, Unlock and Lock. The implementation of critical sections varies among different operating systems, and a synchronization mechanism is required at the entry and exit of the program to ensure exclusive use of critical sections.
In summary, a critical section in operating systems is a segment of code that accesses shared resources and must be executed atomically by multiple...
