1. Loosely-coupled Distributed Reactive
Programming in Mobile Ad Hoc Networks
Andoni Lombide Carreton, Stijn Mostinckx,
Tom Van Cutsem and Wolfgang De Meuter
Department of Computer Science
Vrije Universiteit Brussel
48th International Conference on Objects, Models, Components, Patterns -- TOOLS 2010
June 28 - July 2 2010
Malàga, Spain
Tuesday 29 June 2010

2. The mobile ticket trader application
Tuesday 29 June 2010

3. Pervasive Computing and Mobile Ad Hoc
Networks
Tuesday 29 June 2010

4. Pervasive Computing and Mobile Ad Hoc
Networks
Mobile devices
Tuesday 29 June 2010

5. Pervasive Computing and Mobile Ad Hoc
Networks
Mobile devices
Tuesday 29 June 2010

6. Pervasive Computing and Mobile Ad Hoc
Networks
Mobile devices
Intermittent connectivity
Tuesday 29 June 2010

7. Pervasive Computing and Mobile Ad Hoc
Networks
Mobile devices
Spontaneous interactions
Intermittent connectivity
Tuesday 29 June 2010

8. Pervasive Computing and Mobile Ad Hoc
Networks
Scarce infrastructure
Mobile devices
Spontaneous interactions
Intermittent connectivity
Tuesday 29 June 2010

9. Pervasive Computing and Mobile Ad Hoc
Networks
Scarce infrastructure
Mobile devices
Representation of physical objects
Spontaneous interactions
Intermittent connectivity
Tuesday 29 June 2010

10. Pervasive Computing and Mobile Ad Hoc
Networks
Representation of physical objects
Mobile devices
Spontaneous interactions
Distributed
Event-driven Architecture
Scarce infrastructure
Intermittent connectivity
Tuesday 29 June 2010

11. Pervasive Computing and Mobile Ad Hoc
Networks
Representation of physical objects
Mobile devices
Spontaneous interactions
overy
o c Disc
Ad H Distributed
Event-driven Architecture
Scarce infrastructure
Intermittent connectivity
Tuesday 29 June 2010

12. Pervasive Computing and Mobile Ad Hoc
Networks
Representation of physical objects
Mobile devices
Spontaneous interactions
overy
o c Disc
Ad H Distributed
Event-driven Architecture
Scarce infrastructure
ecent ralized
D Intermittent connectivity
Tuesday 29 June 2010

13. Pervasive Computing and Mobile Ad Hoc
Networks
Representation of physical objects
Mobile devices
Spontaneous interactions
overy
o c Disc
Ad H Distributed
Event-driven Architecture
Res
ilien
Scarce infrastructure t
ecent ralized
D Intermittent connectivity
Tuesday 29 June 2010

14. Pervasive Computing and Mobile Ad Hoc
Networks
Representation of physical objects
Mobile devices
Spontaneous interactions
Event streams
overy
o c Disc
Ad H Distributed
Event-driven Architecture
Res
ilien
Scarce infrastructure t
ecent ralized
D Intermittent connectivity
Tuesday 29 June 2010

15. Pervasive Computing and Mobile Ad Hoc
Networks
Representation of physical objects
Mobile devices
Event streams
Spontaneous interactions
as ting
ro adc
overy B
o c Disc
Ad H Distributed
Event-driven Architecture
Res
ilien
Scarce infrastructure t
ecent ralized
D Intermittent connectivity
Tuesday 29 June 2010

16. Distributed Event-driven Architecture
• Spontaneous discovery of nearby peers
and their ticket offers
• Disconnection/reconnection
• Location of interesting peers changed
• Own location changed
• Price of interesting ticket offers changed
Tuesday 29 June 2010

17. Event Loop Concurrency in AmbientTalk
Tuesday 29 June 2010

18. Event Loop Concurrency in AmbientTalk
“do m immediately”
obj.m()
obj
Tuesday 29 June 2010

19. Event Loop Concurrency in AmbientTalk
“do m eventually”
obj<-m()
Tuesday 29 June 2010

20. Event Loop Concurrency in AmbientTalk
“do m eventually”
obj<-m()
Tuesday 29 June 2010

21. Event Loop Concurrency in AmbientTalk
?
future
Tuesday 29 June 2010

22. Event Loop Concurrency in AmbientTalk
?
future
when: future becomes: { |value|
// process reply
}
Tuesday 29 June 2010

23. Event Loop Concurrency in AmbientTalk
?
future
when: future becomes: { |value|
// process reply
}
Tuesday 29 June 2010

24. Publishing & discovering objects by topic
ticketVendor
Tuesday 29 June 2010

25. Publishing & discovering objects by topic
ticketVendor
deftype TicketVendor deftype TicketVendor
Tuesday 29 June 2010

26. Publishing & discovering objects by topic
ticketVendor
deftype TicketVendor deftype TicketVendor
export: ticketVendor as: TicketVendor
Tuesday 29 June 2010

27. Publishing & discovering objects by topic
ticketVendor
deftype TicketVendor deftype TicketVendor
export: ticketVendor as: TicketVendor
whenever: TicketVendor discovered: { |ticketVendor|
// React on ticketVendor appearance
when: ticketVendor disconnected: {
// React on disappearance
}
when: ticketVendor reconnected: {
// React on reappearance
}}
Tuesday 29 June 2010

28. Publishing & discovering objects by topic
ticketVendor
deftype TicketVendor deftype TicketVendor
export: ticketVendor as: TicketVendor
whenever: TicketVendor discovered: { |ticketVendor|
// React on ticketVendor appearance
when: ticketVendor disconnected: {
// React on disappearance
}
when: ticketVendor reconnected: {
// React on reappearance
}}
Tuesday 29 June 2010

29. Publishing & discovering objects by topic
ticketVendor
deftype TicketVendor deftype TicketVendor
export: ticketVendor as: TicketVendor
whenever: TicketVendor discovered: { |ticketVendor|
// React on ticketVendor appearance
covery
when: ticketVendor disconnected: {
// React on disappearance
Ad H oc Dis
}
when: ticketVendor reconnected: {
// React on reappearance
}}
Tuesday 29 June 2010

30. Publishing & discovering objects by topic
ticketVendor
deftype TicketVendor deftype TicketVendor
export: ticketVendor as: TicketVendor
whenever: TicketVendor discovered: { |ticketVendor|
// React on ticketVendor appearance
covery
when: ticketVendor disconnected: {
// React on disappearance
Ad H oc Dis
}
when: ticketVendor reconnected: { alized
// React on reappearance D ecentr
}}
Tuesday 29 June 2010

31. Asynchronous communication
getLocation
ticketVendor
when: TicketVendor discovered: { |ticketVendor|
when: ticketVendor<-getLocation()@Due(timeout) becomes: { |loc|
// Update user interface with the location
} catch: TimeoutException using: { |e|
// Remove ticket offer from user interface
}
}
Tuesday 29 June 2010

32. Asynchronous communication
getLocation
ticketVendor
when: TicketVendor discovered: { |ticketVendor|
when: ticketVendor<-getLocation()@Due(timeout) becomes: { |loc|
// Update user interface with the location
} catch: TimeoutException using: { |e|
// Remove ticket offer from user interface
}
}
Tuesday 29 June 2010

33. Asynchronous communication
getLocation
ticketVendor
when: TicketVendor discovered: { |ticketVendor|
when: ticketVendor<-getLocation()@Due(timeout) becomes: { |loc|
// Update user interface with the location
} catch: TimeoutException using: { |e|
// Remove ticket offer from user interface
}
}
Tuesday 29 June 2010

34. Asynchronous communication
ticketVendor
when: TicketVendor discovered: { |ticketVendor|
when: ticketVendor<-getLocation()@Due(timeout) becomes: { |loc|
// Update user interface with the location
} catch: TimeoutException using: { |e|
// Remove ticket offer from user interface
}
}
Tuesday 29 June 2010

35. Asynchronous communication
ticketVendor
when: TicketVendor discovered: { |ticketVendor|
when: ticketVendor<-getLocation()@Due(timeout) becomes: { |loc|
// Update user interface with the location
} catch: TimeoutException using: { |e|
// Remove ticket offer from user interface
}
}
Tuesday 29 June 2010

36. Asynchronous communication
ticketVendor
when: TicketVendor discovered: { |ticketVendor|
when: ticketVendor<-getLocation()@Due(timeout) becomes: { |loc|
// Update user interface with the location
} catch: TimeoutException using: { |e|
// Remove ticket offer from user interface
}
}
Tuesday 29 June 2010

37. Asynchronous communication
ticketVendor
Res
ilien
t
when: TicketVendor discovered: { |ticketVendor|
when: ticketVendor<-getLocation()@Due(timeout) becomes: { |loc|
// Update user interface with the location
} catch: TimeoutException using: { |e|
// Remove ticket offer from user interface
}
}
Tuesday 29 June 2010

38. Ambient References
ting
werchterVendors
as
ro adc
B
def werchterVendors := ambient: TicketVendor where: { |tv|
tv.event == “Rock Werchter”
};
whenAll: werchterVendors<-getLocation()@Expires(5.seconds)
becomes: { |locations|
// Update the map GUI with the locations
}
Tuesday 29 June 2010

39. Ambient References
ting
werchterVendors
as
ro adc
B
def werchterVendors := ambient: TicketVendor where: { |tv|
tv.event == “Rock Werchter”
};
whenAll: werchterVendors<-getLocation()@Expires(5.seconds)
becomes: { |locations|
// Update the map GUI with the locations
}
Tuesday 29 June 2010

40. AmbientTalk/R
gui.centerOn(GPS_Location.latitude, GPS_Location.longitude);
GPS_Location
_.latitude _.longitude
latitude longitude
gui.centerOn(_, _)
Tuesday 29 June 2010

41. AmbientTalk/R
gui.centerOn(GPS_Location.latitude, GPS_Location.longitude);
GPS_Location
_.latitude _.longitude
latitude longitude
gui.centerOn(_, _)
Tuesday 29 June 2010

42. AmbientTalk/R
gui.centerOn(GPS_Location.latitude, GPS_Location.longitude);
GPS_Location
_.latitude _.longitude
latitude longitude
gui.centerOn(_, _)
Tuesday 29 June 2010

43. AmbientTalk/R
def Coordinate := isolate: {
def latitude := 0;
def longitude := 0;
def distanceTo(anotherCoordinate) {
// Compute via Haversine formula
};
def @Mutator update(newLatitude, newLongitude) {
latitude := newLatitude;
longitude := newLongitude;
};
};
def GPS_Location := makeReactive(Coordinate.new());
GPS.addLocationObserver: { |lat, lon|
GPS_Location
GPS_Location.update(lat, lon)
};
Tuesday 29 June 2010

44. AmbientTalk/R
def Coordinate := isolate: {
def latitude := 0;
def longitude := 0;
def distanceTo(anotherCoordinate) {
// Compute via Haversine formula
};
def @Mutator update(newLatitude, newLongitude) {
latitude := newLatitude;
longitude := newLongitude;
}; Event streams
};
def GPS_Location := makeReactive(Coordinate.new());
GPS.addLocationObserver: { |lat, lon|
GPS_Location
GPS_Location.update(lat, lon)
};
Tuesday 29 June 2010

45. Ambient Behaviors
exportBehavior: GPS_Location as: TicketVendorLocation
to: { |buyer| buyer.interestedIn == “Rock Werchter” };
GPS_Location
_.latitude _.longitude
GUI.showLocationOnM vendorLocation
latitude longitude
gui.centerOn
(_, _)
vendorLocation
def @Any vendorLocation := ambientBehavior: TicketVendorLocation
where: { def interestedIn := “Rock Werchter” };
Tuesday 29 June 2010

46. Ambient Behaviors
exportBehavior: GPS_Location as: TicketVendorLocation
to: { |buyer| buyer.interestedIn == “Rock Werchter” };
TicketVendorLocation
GPS_Location
_.latitude _.longitude
GUI.showLocationOnM vendorLocation
latitude longitude
gui.centerOn
(_, _)
vendorLocation
def @Any vendorLocation := ambientBehavior: TicketVendorLocation
where: { def interestedIn := “Rock Werchter” };
Tuesday 29 June 2010

47. Ambient Behaviors
exportBehavior: GPS_Location as: TicketVendorLocation
to: { |buyer| buyer.interestedIn == “Rock Werchter” };
TicketVendorLocation
GPS_Location
_.latitude _.longitude
GUI.showLocationOnM vendorLocation
latitude longitude
gui.centerOn
(_, _)
vendorLocation
def @Any vendorLocation := ambientBehavior: TicketVendorLocation
where: { def interestedIn := “Rock Werchter” };
Tuesday 29 June 2010

48. Ambient Behaviors
exportBehavior: GPS_Location as: TicketVendorLocation
to: { |buyer| buyer.interestedIn == “Rock Werchter” };
TicketVendorLocation
GPS_Location
_.latitude _.longitude
GUI.showLocationOnM vendorLocation
latitude longitude
gui.centerOn
(_, _)
vendorLocation
def @Any vendorLocation := ambientBehavior: TicketVendorLocation
where: { def interestedIn := “Rock Werchter” };
Tuesday 29 June 2010

49. Ambient Behaviors
exportBehavior: GPS_Location as: TicketVendorLocation
to: { |buyer| buyer.interestedIn == “Rock Werchter” };
TicketVendorLocation
GPS_Location
_.latitude _.longitude
GUI.showLocationOnM vendorLocation
latitude longitude
vendorLocation
gui.centerOn
(_, _)
vendorLocation
def @Any vendorLocation := ambientBehavior: TicketVendorLocation
where: { def interestedIn := “Rock Werchter” };
Tuesday 29 June 2010

50. Ambient Behaviors
exportBehavior: GPS_Location as: TicketVendorLocation
to: { |buyer| buyer.interestedIn == “Rock Werchter” };
TicketVendorLocation
GPS_Location
_.latitude _.longitude
GUI.showLocationOnM vendorLocation
latitude longitude
vendorLocation
gui.centerOn
(_, _)
vendorLocation
def @Any vendorLocation := ambientBehavior: TicketVendorLocation
where: { def interestedIn := “Rock Werchter” };
Tuesday 29 June 2010

51. Ambient Behaviors
exportBehavior: GPS_Location as: TicketVendorLocation
to: { |buyer| buyer.interestedIn == “Rock Werchter” };
GPS_Location
vendorLocations
vendorLocations
GPS_Location
vendorLocations
def @All vendorLocations := ambientBehavior: TicketVendorLocation
where: { def interestedIn := “Rock Werchter” } timeout: 2000;
Tuesday 29 June 2010

52. Ambient Behaviors
exportBehavior: GPS_Location as: TicketVendorLocation
to: { |buyer| buyer.interestedIn == “Rock Werchter” };
GPS_Location
vendorLocations
GPS_Location
vendorLocations
GPS_Location
vendorLocations
def @All vendorLocations := ambientBehavior: TicketVendorLocation
where: { def interestedIn := “Rock Werchter” } timeout: 2000;
Tuesday 29 June 2010

53. Ambient Behaviors
exportBehavior: GPS_Location as: TicketVendorLocation
to: { |buyer| buyer.interestedIn == “Rock Werchter” };
GPS_Location
vendorLocations
GPS_Location
vendorLocations
GPS_Location
vendorLocations
def @All vendorLocations := ambientBehavior: TicketVendorLocation
where: { def interestedIn := “Rock Werchter” } timeout: 2000;
Tuesday 29 June 2010

54. Ambient Behaviors
exportBehavior: GPS_Location as: TicketVendorLocation
to: { |buyer| buyer.interestedIn == “Rock Werchter” };
GPS_Location
vendorLocations
vendorLocations
GPS_Location
vendorLocations
def @All vendorLocations := ambientBehavior: TicketVendorLocation
where: { def interestedIn := “Rock Werchter” } timeout: 2000;
Tuesday 29 June 2010

55. Ambient Behaviors
def findOffers(event, maxPrice, maxDistance) {
// Subscribe to ticket offers
def @All allNearbyOffers := ambientBehavior: TicketOfferT timeout: 2000;
// Filter out interesting ticket offers
allNearbyOffers.filter: { |offer|
(offer.eventName == event).and: {
(offer.price <= maxPrice).and: {
GPS_Location.distanceTo(offer.location) <= maxDistance }}};
};
• Disconnection/reconnection
• Location of interesting peers changed
def werchterVendors :=
findOffers(“Rock Werchter”, 120, 500);
• Own location changed
gui.updateWithOffers(werchterVendors);
• Price of interesting ticket offers changed
Tuesday 29 June 2010

56. Reactive Queries
werchterVendors
def werchterVendors := ambient: TicketVendor where: { |tv|
tv.event == “Rock Werchter”
};
def locations := werchterVendors<-getLocation()@Refresh(2.seconds);
locations.each:
{ |coordinates| GUI.showLocationOnMap(coordinates) };
Tuesday 29 June 2010

57. Reactive Queries
werchterVendors
def werchterVendors := ambient: TicketVendor where: { |tv|
tv.event == “Rock Werchter”
};
def locations := werchterVendors<-getLocation()@Refresh(2.seconds);
locations.each:
{ |coordinates| GUI.showLocationOnMap(coordinates) };
Tuesday 29 June 2010

58. Limitations and Future Work
• AmbientTalk/R yields a higher computational overhead than plain
AmbientTalk.
• Event message order preservation not guaranteed on very fine-grained levels
over different communication partners.
• No real-time guarantees.
• Event consumers can only create and cancel their distributed dependencies:
they cannot limit the number of propagated events.
Tuesday 29 June 2010

59. Conclusion
• Decentralized publish/subscribe architecture based on UDP broadcasting
allows spontaneous and loosely-coupled group interactions.
• Reactive interpreter allows reacting to and processing of events without
relying on “callback-spaghetti”.
• Ambient behaviors and reactive queries reconcile both programming styles.
• Event propagation happens with asynchronous messages among distributed
event loops: no concurrency issues and resilient to intermittent network
connectivity.
http://soft.vub.ac.be/soft/research/amopcop
Tuesday 29 June 2010