Concurrent Models and Distributed Algorithms BenOr Algorithm A randomized algorithm for solving the consensus problem in asynchronous systems

1. BenOr Simulation

2. Initial State
Process
Number: 6
x = initial value
y = final value

3. (step k = 0)
init(v) on all port

4. Reporting phase:
First step: k = 1
each process
send m(R, 1, *)
P6 → crash

5. Reporting phase
(R, k = 1)
no consensus
1) wait n – f process messages
2) n – f different messages
3) send (P, k = 1, y = ?)
All processes send m (P, k = 1, y = ?)

6. Propose phase
(P, k = 1)
1) wait n – f process messages
2) case 3: y = ? → random choice
(0 or 1)
P1 = 1, P2 = 1, P3= 1, P4 = 1, P5 = 1
k = k + 1 = 2

7. Reporting phase
(R, k = 2)
each process
send m(R, 1, *)

8. Reporting phase
(R, k = 2)
1) wait n – f process messages
2) same y
3) all process send m (P, k =2, y = 1)

9. Propose phase
(P, k = 2)
1) wait n – f process messages
2) case 1: same v
3) all process → decide(y)

10. Consensus OK!

11. BenOr Simulation - END