LAMPORT’S ALGORITHM

BY

Neelamani Samal

What is Lamport’s Algorithm

• It is a computer algorithm

• Intended to improve the safety in the

usage of shared resources

•  Using mutual exclusion.

Related Terms

• Mutual exclusion

• Types of mutual exclusion algorithm

• Critical Section(C.S.)

• Logical Clock

• Causal Ordering Of Messages

Algorithm

• Every site Si keeps a request_queuei,

• contains mutual exclusion requests ordered by their timestamps

• messages to be delivered in the FIFO order between every pair of sites

System Models

• Requesting The C.S.

• Executing The C.S.

• Releasing The C.S.`

Example

• We have S1,S2,S3 as sites

• S1,S2 request for CS

• S2 Being first

S1

S2

S3

(1,2)

(2,1)

S1,S2 making requesr for entering CS

S1

S2

S3

(1,2)

(2,1)

Site S2 enters CS

(1,2) (1,2),(2,1)

(1,2),(2,1)

(1,2),(2,1)

S2 enters CS

S1

S2

S3

(1,2)

(2,1)

Site S2 exitsCS and release message

(1,2) (1,2),(2,1)

(1,2),(2,1)

(1,2),(2,1)

S2 exits CS

S1

S2

S3

(1,2)

(2,1)

Site S1 entersCS

(1,2) (1,2),(2,1)

(1,2),(2,1)

(1,2),(2,1)

S1enters CS

(2,1)

(2,1)

Performance Analysis

• Total No. of REQUEST (N-1)

• Total No. Of REPLY (N-1)

• Total No. Of RELEASE (N-1)

• Total = 3(N-1)

Conclusion

Though it does not explain the Modern scenario of distributed

systems but , it gave the basic of developing the present way

of handling distributed resources.