Lamport's Distributed Mutual Exclusion Algorithm is a contention-based algorithm for mutual exclusion on a distributed system.
Contents
Nodal properties
- Every process maintains a queue of pending requests for entering critical section in order. The queues are ordered by virtual time stamps derived from Lamport timestamps.
Algorithm
Requesting process
- Pushing its request in its own queue (ordered by time stamps)
- Sending a request to every node.
- Waiting for replies from all other nodes.
- If own request is at the head of its queue and all replies have been received, enter critical section.
- Upon exiting the critical section, remove its request from the queue and send a release message to every process.
Other processes
- After receiving a request, pushing the request in its own request queue (ordered by time stamps) and reply with a time stamp.
- After receiving release message, remove the corresponding request from its own request queue.
- If own request is at the head of its queue and all replies have been received, enter critical section.
Message complexity
This algorithm creates 3(N − 1) messages per request, or (N − 1) messages and 2 broadcasts. 3(N − 1) messages per request includes:
Drawbacks
There exist multiple points of failure.
References
Lamport's distributed mutual exclusion algorithm Wikipedia(Text) CC BY-SA