Virtual Net: A Decentralized Architecture for Interaction in Mobile Virtual Worlds

Algorithm 7

Leader election.

1. On any replica:

2. Upon r_L∉R ∧ r_c ≠ self

3.  LE ← true

4.  r_c ← SelectLeader()

5.  If r_c = self then

6.   Reliably broadcast LE_QUERY to G∩R

7.

8. SelectLeader()

9.  R_c  :=

10.  If = 1, then

11.   Return r_i: r_i∈R_c

12.  Else

13.   Return r_i: r_i∈R_c  ∧ r_i.ID =

14.

15.

16 Upon LE_QUERY from r_c

17.  If r_c∈R ∧ r_c = SelectLeader(), then

18.   LE ← true

19.   LE_STATE ← (Q_d, E, cid, G, epoch)

20.   Reliably send LAST_STATE to r_c

21.  Else

22.   Reliably send NACK to r_c

23.

24. Upon LOAD_LEADER(Q_d’, E’, epoch’, cid’, G’, Init)

    from r_c  ∧ r_c∈R ∧ r_c = SelectLeader()

25.  (Q_d, E, cid, G, epoch) ← (Q_d’, E’, cid’, G’, epoch’ + 1)

26.  (r_L, r_c) ← (r_c, ⊥)

27.  LE ← false

28.  If newReplica = true, then                 // New replica initialization is

29.   Initialize(Init)                      needed, in case that a group

30.   newReplica ← false                   reconfiguration is interrupted

                              by a leader election

31.

32.

33. Upon NACK from r_i

34.  If self = Selectleader()

35.   Reliably send LE_QUERY to r_i

36.  Else

37.   r_c ← ⊥

38.

39. Upon LE_STATE(Q_d,i, E_i, cid_i, G_i, epoch_i) from r_i

40.  Events←Events∪  

41.  Decisions←Decision∪  

42.  Configs←Configs∪  

43.  Epochs←Epochs∪  

44.  Senders←Senders∪  

45.

46. Upon G∩R ⊆ Senders

47.  Q_d ← Longest(Events)

48.  E ← Merge(Decisions)

49.   (cid, G) ← Latest(Configs)

50.  epoch ← Latest(Epochs)

51.  Init← (t₀,, (λ_c, state),          // state: current application

    ,S)                          state

52.  LOAD_ LEADER ← (Q_d, E, epoch, cid, G, Init)

53.  Reliably broadcast LOAD_LEADER to G∩R

54.  Broadcast G to S