	US 7,580,997 B2
	State recovery
Keith Sterling, London (United Kingdom); Richard Hughes, London (United Kingdom); Allan Jenkins, London (United Kingdom); William Box, London (United Kingdom); and Ian Middleton, London (United Kingdom)
Assigned to Jacobs Rimell Limited, London (United Kingdom)
Appl. No. 10/492,551 PCT Filed Oct. 15, 2002, PCT No. PCT/GB02/04667 § 371(c)(1), (2), (4) Date Apr. 14, 2004, PCT Pub. No. WO03/034223, PCT Pub. Date Apr. 24, 2003.
Claims priority of application No. 0124702.2 (GB), filed on Oct. 15, 2001.
Prior Publication US 2005/0044239 A1, Feb. 24, 2005
Int. Cl. G06F 15/173 (2006.01)

U.S. Cl. 709—224 [709/227; 709/228; 700/1; 700/5; 700/12; 711/100; 711/5; 711/111]

15 Claims

1. A method of recovering a modeled state of an entity in a distributed networked system following failure and recovery of an entity monitoring application, which said entity monitoring application comprises a counter, which said counter represents the modeled state of the entity in the system, comprising the steps of:

(a) incrementing the counter in response to receiving an increment request to increment the state of the entity;

(b) determining, in response to receiving a decrement request to decrement the state of the entity, if the decrement request is paired with an increment request received subsequent to the recovery of the entity monitoring application, and:

if so, then decrementing the counter; and

if not, then discarding the decrement request such that the decrement request has no effect on the counter; and

(c) repeating steps (a) and (b) such that the modeled state of the entity converges with a true state of the entity as all decrement requests not paired with the increment request received subsequent to the recovery of the entity monitoring application are discarded;

wherein the counter refers to a number of concurrent user sessions;

wherein the counter is implemented in volatile memory;

wherein the system comprises a plurality of entities and the entity monitoring application comprises a plurality of counters corresponding to the plurality of entities.