Friday, December 3, 1993

Distributed Coordination

Ring algorithm to elect a new coordinator (section 13.7.2)

Requires n^2 messages for n the number of processes in the system
Messages passing from left to right on ring on unidirectional links
Each process has a unique priority number
The goal is to find the process with the highest priority number and inform all
	processes of this fact
Each process has an active list containing the priority numbers of all active
	processes in the system

If Pi detects coordinator failure
	create a new active list, initially empty
	send elect(i) to right neighbor
	add i to active list

If Pi receives message elect(j) from left neighbor, must respond in one of
three ways:
	- if this is first elect message Pi has seen or sent
		create a new active list
		add i and j to the active list
		send elect(i) to right neighbor
		send elect(j) to right neighbor
	- if i <> j (elect(j) does not contain Pi's number)
		add j to active list
		send elect(j) to right neighbor
	- if i == j (message received is elect(i)) then active list for Pi
		contains all active processes' priority numbers
		largest number is now new coordinator
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