Distributed Reactive Programming Tools2010

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 ScienceVrije Universiteit Brussel

48th International Conference on Objects, Models, Components, Patterns -- TOOLS 2010June 28 - July 2 2010Malàga, Spain

Tuesday 29 June 2010

The mobile ticket trader application


Pervasive Computing and Mobile Ad Hoc Networks



Mobile devices



Mobile devices

Intermittent connectivity



Mobile devices


Spontaneous interactions



Mobile devices


Scarce infrastructure




Mobile devices



Representation of physical objects



Distributed Event-driven Architecture






Mobile devices








Mobile devices

Ad Hoc Discovery








Mobile devices

Decentralized

Ad Hoc Discovery








Mobile devices

Decentralized

Resilient

Ad Hoc Discovery








Mobile devices

Event streams

Decentralized

Resilient

Ad Hoc Discovery








Mobile devices

Event streams

Decentralized

Resilient

Ad Hoc Discovery Broadcasting



• 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


Event Loop Concurrency in AmbientTalk



“do m immediately”

obj

obj.m()



“do m eventually”

obj<-m()



?

future



?

future

when: future becomes: { |value| // process reply}


Publishing & discovering objects by topic

ticketVendor



ticketVendor

deftype TicketVendor deftype TicketVendor



ticketVendor

export: ticketVendor as: TicketVendordeftype TicketVendor deftype TicketVendor



ticketVendor

export: ticketVendor as: TicketVendorwhenever: TicketVendor discovered: { |ticketVendor| // React on ticketVendor appearance when: ticketVendor disconnected: { // React on disappearance } when: ticketVendor reconnected: { // React on reappearance }}




ticketVendor



Ad Hoc Discovery



ticketVendor



Ad Hoc Discovery

Decentralized


Asynchronous communication

ticketVendor

getLocation

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 }}



ticketVendor




ticketVendor


Resilient


Ambient References

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 }

werchterVendors

Broadcasting


AmbientTalk/R

gui.centerOn(GPS_Location.latitude, GPS_Location.longitude);

GPS_Location

latitude longitude

_.latitude _.longitude

gui.centerOn(_, _)

GPS_Location


AmbientTalk/R


GPS_Location

latitude longitude


gui.centerOn(_, _)


latitude longitude


AmbientTalk/R


GPS_Location

latitude longitude


gui.centerOn(_, _)gui.centerOn(_, _)


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.update(lat, lon)};

GPS_Location


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.update(lat, lon)};

GPS_Location

Event streams


vendorLocation

vendorLocation

Ambient Behaviors

exportBehavior: GPS_Location as: TicketVendorLocation to: { |buyer| buyer.interestedIn == “Rock Werchter” };

def @Any vendorLocation := ambientBehavior: TicketVendorLocation where: { def interestedIn := “Rock Werchter” };

GUI.showLocationOnM

GPS_Location


latitude longitude

gui.centerOn(_, _)


vendorLocation

vendorLocation

TicketVendorLocation

Ambient Behaviors



GUI.showLocationOnM

GPS_Location


latitude longitude

gui.centerOn(_, _)


vendorLocation

vendorLocation

vendorLocation

TicketVendorLocation

Ambient Behaviors



GUI.showLocationOnM

GPS_Location


latitude longitude

gui.centerOn(_, _)


vendorLocations

vendorLocations

vendorLocations

Ambient Behaviors


def @All vendorLocations := ambientBehavior: TicketVendorLocation where: { def interestedIn := “Rock Werchter” } timeout: 2000;

GPS_Location

GPS_Location


vendorLocations

vendorLocations

vendorLocations

Ambient Behaviors



GPS_Location

GPS_Location

GPS_Location


vendorLocations

vendorLocations

vendorLocations

Ambient Behaviors



GPS_Location

GPS_Location


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

• Own location changed

• Price of interesting ticket offers changed

def werchterVendors := findOffers(“Rock Werchter”, 120, 500);

gui.updateWithOffers(werchterVendors);


Reactive Queries

def werchterVendors := ambient: TicketVendor where: { |tv| tv.event == “Rock Werchter”};

def locations := werchterVendors<-getLocation()@Refresh(2.seconds);

locations.each: { |coordinates| GUI.showLocationOnMap(coordinates) };

werchterVendors


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.


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/amopcopTuesday 29 June 2010

http://soft.vub.ac.be/soft/research/amopcop

http://soft.vub.ac.be/soft/research/amopcop

Distributed Reactive Programming Tools2010

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