Mutual Exclusion

Mutual Exclusion is a property of process synchronization that states that “no two processes can exist in the critical section at any given point of time”. The term was first coined by Dijkstra. Any process synchronization technique being used must satisfy the property of mutual exclusion, without which it would not be possible to get rid of a race condition. 

The need for mutual exclusion comes with concurrency. There are several kinds of concurrent execution:

1. Interrupt handlers
2. Interleaved, preemptively scheduled processes/threads
3. Multiprocessor clusters, with shared memory
4. Distributed systems

Mutual exclusion methods are used in concurrent programming to avoid the simultaneous use of a common resource, such as a global variable, by pieces of computer code called critical sections •

The requirement of mutual exclusion is that when process P1 is accessing a shared resource R1, another process should not be able to access resource R1 until process P1 has finished its operation with resource R1.

Examples of such resources include files, I/O devices such as printers, and shared data structures.

During concurrent execution of processes, processes need to enter the critical section (or the section of the program shared across processes) at times for execution. It might happen that because of the execution of multiple processes at once, the values stored in the critical section become inconsistent. In other words, the values depend on the sequence of execution of instructions – also known as a race condition. The primary task of process synchronization is to get rid of race conditions while executing the critical section.

This is primarily achieved through mutual exclusion.