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Ricart–Agrawala Algorithm (Distributed Mutual Exclusion)

The Ricart–Agrawala Algorithm is a distributed mutual exclusion algorithm designed to allow processes in a distributed system to agree on accessing a shared resource without central coordination. It was introduced by R. Ricart and A. Agrawala in 1981 and is based on message passing for synchronization and mutual exclusion.

Description:

Each process in the system sends a request message to all other processes, asking for permission to enter the critical section. Processes respond with a reply only if they are not requesting the critical section or if their request has a higher priority (timestamp). A process can enter the critical section only when it has received a reply from all other processes, indicating no conflict. This algorithm uses timestamps to order the requests and resolve conflicts, ensuring that the process with the earliest timestamp is granted access first.

Key Points:

Distributed approach: No central coordinator is needed. Message passing for synchronization. Uses timestamps to ensure fair access.

Source: Ricart, G., & Agrawala, A. (1981). "An Optimal Algorithm for Mutual Exclusion in a Distributed System". ACM Transactions on Computer Systems.