Download - Programming with Live Distributed Objects

TRUST Autumn 2008 Conference: November 11-12, 2008

Programming with Live Distributed Objects

Krzysztof Ostrowski†

in collaboration with

Ken Birman†, Danny Dolev§, Jong Hoon Ahnn†

†Cornell University, §Hebrew University

http://liveobjects.cs.cornell.edu

TRUST Autumn 2008 Conference: November 11-12, 2008“Live Objects", Krzysztof Ostrowski 2

Introduction


Modern Software Development

“Live Objects", Krzysztof Ostrowski 3

reusable, replaceablecomponents

developer

shared

documentreplicated

datadistributedlock reliab

lemulticast

A

B

C D

application

object-orientation

typedcontracts


Object-Orientation has Benefits


rapid drag-and-drop visual design

in a managed, typed OO environment(Java, .NET, COM)

developer

shared

documentreplicated


lemulticast

A

B

C D

application

reusabilityexamplebenefits modularity, decoupling

type safetybehavioral reflection

more conceptual design


Object-Orientation has Benefits




developer

shared

documentreplicated


lemulticast

A

B

C D

application





Distributed Systems: Out of Luck




developer

shared

documentreplicated


lemulticast

A

B

C D

application





Building a Collaborative App


shareddocument




replicationmiddleware

update




replicationmiddleware

obtaindocument

copy


Using Obscure, Proprietary APIs


ssize_t recvfrom( int socket, void *buffer, size_t length, int flags, struct sockaddr *address, socklen_t *address_len);

Channel channel = new JChannel( "UDP:PING:FD:STABLE:NAKACK:UNICAST:" + "FRAG:FLUSH:GMS:VIEW_ENFORCER:” + "STATE_TRANSFER:QUEUE");

obscureproprietary

low-level

confusing


Tightly Coupled Components


ApplicationLayer

MiddlewareLayer

shared

documentreplicated


lemulticast

distributed application

tightlycoupled,unseparable


Many Layers In the Middleware


Layer 1

Layer 2

Layer 3

Layer 4




shared document

replicateddata

distributedlock

reliablemulticast

shared

documentreplicated


lemulticast


distributed components

composition




shared document

replicateddata

distributedlock

reliablemulticast

shared

documentreplicated


lemulticast



composition




shared document

replicateddata

distributedlock

reliablemulticast

shared

documentreplicated


lemulticast

unreliable multicast




shared document

replicateddata

distributedlock

reliablemulticast

shared

documentreplicated


lemulticast


overlay




shared document

replicateddata

distributedlock

shared

documentreplicated


lemulticast


overlaymembership

reliablemulticast




shared document

replicateddata

distributedlock

shared

documentreplicated


lemulticast


overlay

reliablemulticast

membership

failuredetector


Protocols = Components ???


canreuse

reliable multicastchannel

stronglytyped

well-definedcontracts

canreplace

:T1

:T2


…But Not In Java/.NET/COM/*


canreuse

reliable multicastchannel

stronglytyped

well-definedcontracts

canreplace

:T1

:T2


Related Work


Distributed objectsEmerald, Argus, Globus, Linda, F.T. Corba, Croquet

Protocol compositionx-Kernel, Horus, Ensemble, BAST

Protocol typesCSP, π-calculus, BPEL, SSDL, WSCL, CFSM, TLA, IOA, IA, temporal logic,

Protocol specificationsHorus, Ensemble, Chockler et al. [2001]

Distributed environmentsJini, JXTA, WS-* specifications


Related Work








Every Protocol Instance = Object


my custom protocol (class)

runningprotocolinstance(object)

new()


Every Protocol Instance = Object


Internet as a managed environment (runtime)

protocol participant

running instance of a distributed protocol (object)



Objects


Defining Live Distributed Objects


user

computer

local instance of a protocol stack

(“proxy”)

live object




localstate and

logic live object

m m

mm m

m

m

networkmessages




live object

“endpoint” communication & control

interface

black boxcan encapsulate state and threads

of execution

events


Live Objects vs. .NET Objects


ordinaryobject

state & logic




accessprotocol

m m

remote object

mm

m

backendservice

(state & logic)

client

server




remote object

m m

mm

mclient

server

clientm

m

backendservice(state & logic)




m m

(replicated) remote object

mm

m

backend service(state & logic)

client

mm

server1

mm

mm

m

server2




proxies collectively provide “service”to one another

m m

m

m

live object

mm

m

no backend




m m

mm m

m

m

live object

BEHAVIOR

Service = Behavior



References


Creating a Live Object


developer

node1 node2 nodeK

user1 user2 userK




create ina visualdesigner

node1 node2 nodeK

live objectreferenceXML (recipe)




distribute

1. over email,

2. embedded inside of a document,

3. through a shared folder node1 node2 nodeK

------------------------------------------------------------------

------

XML




store referencese.g. as files

node1 node2 nodeK

XML XML XMLXML XMLXMLXMLXML XML XMLXML

XMLXMLXML




dereference(execute)

node1 node2 nodeK

XML XML XMLXML XMLXMLXMLXML XML XMLXML

XMLXMLXML

liveobjectsruntime

liveobjectsruntime

liveobjectsruntime




parse XML,create proxy,run proxy

node1 node2 nodeK

liveobjectsruntime

liveobjectsruntime

liveobjectsruntime

a2a1




runningobject

node1 node2 nodeK

a2a1




node1 node2 nodeK

a2a1

XML

liveobjectsruntime




node1 node2 nodeK

a2a1 aK



Composition


Connecting Objects


c2 c3c1

use the same membership object

membership object

to membership

servicem3m2m1


Connecting Objects


s2 s3s1

c2 c3c1

m1 m2 m3

m4 m5 m6

membership service

“group”object

membership object

client node

servernode


Connecting Objects


a4 a5 a6

client endpoints

a1 a2 a3

C C C

C C C

S S S

S S S

server endpoints


Dependencies as Endpoints


fj

dk

ai

membershipobject

discoveryobject

cl

failuredetectorobject

node

yourobject


Creating Composite Objects


x2 x3x1

y1 y2 y3 XML

XMLreference to x

reference to y

compositereference

instructions to connect endpoints




liveobjectsruntime

XML

XMLreference to x

reference to y

activate

this is happening on a single machine




liveobjectsruntime

XML

XMLreference to x

reference to y

infer type

infer type





liveobjectsruntime

XML

XMLreference to x

reference to y

: θXML

XML : θ'A

Binfer types ofA and B





liveobjectsruntime

XML

XMLreference to x

reference to y

: θXML

XML : θ'A

B

B : τ'

A : τ

test

τ µ τ'

can endpoint of type τ

be connected to endpoint of type τ'

???




liveobjectsruntime

XML

XMLreference to x

reference to y

x1

create proxy of x





liveobjectsruntime

XML

XMLreference to x

reference to y

x1

create proxy of y

y1





liveobjectsruntime

XML

XMLreference to x

reference to y

x1

connectproxies

y1





XML

liveobjectsruntime

XMLXML

XML

y1

z1

x1

v1



Compatibility


Defining Endpoint Types


x1

y1

A

B

is thislegal?




x1

y1

A:τ

B:τ'

endpoint of type τ

endpoint of type τ'




x1

y1

A:τ

B:τ'τ µ τ'

compatible

???




event : e event' : e'e e'

θ θ'τ τ'

Can we connect A: and B:‘ ?




event : e event' : e'e e'

θ θ'τ τ'

Provided Required'

θ θ'τ τ'

Provided Þ Required'


Defining Live Object Types


IP multicast

θ

channel:τ

receive:ɛreceive

send:ɛsend

θ:Reliable atomic broadcastθ:

sametype

wildly different semantics



Types




live objecttype

A:τ

B:τ'

C:τ"

θ

θ=(E, … )

E={A:τ,B:τ',C:τ"}list of endpoints:




live objecttype

A:τ

B:τ'

C:τ"

θ

θ=(E, … )

E={A:τ,B:τ',C:τ"}endpoint

type

list of endpoints:

A:τ

B:τ'C:τ"

A:τ

B:τ'C:τ"

A:τ

B:τ'C:τ"

every proxy must have endpoints A:τ,B:τ',C:τ"




live objecttype

A:τ

B:τ'

C:τ"

θ

θ=(E, … )

E={A:τ,B:τ',C:τ"}

receive:ɛreceive

view:ɛview

send:ɛsend

leave:ɛleave

join:ɛjoin

τ=(I, O, … )endpoint

type

list of endpoints:

input events

outputevents


Behavioral Constraints


live objecttype

A:τ

B:τ'

C:τ"

θ

θ=(E,Pθ,Rθ)

constraints provided constraints required

E={A:τ,B:τ',C:τ"}

receive:ɛreceive

view:ɛview

send:ɛsend

leave:ɛleave

join:ɛjoin

τ=(I,O,Pτ,Rτ)endpoint

type

list of endpoints:

input events

outputevents

constraints provided

constraints required




[ObjectConstraint(“Security”, “Level=5”)][ObjectClass(“Channel”)]interface Channel {

[EndpointConstraint(“Order”, “Total”)][Endpoint(“C”)]ChannelEndpoint C { get; }

}

annotation

alias for a live object type



Constraints




A:τ

B:τ'

C:τ"

θ

A:τ A:τ A:τ

structure we’ve defined:the world of events

that occur atinstances of endpoint A




A:τ

B:τ'

C:τ"

θ

A:τ A:τ A:τ

occurs...everywhere...somewhere...

span across instancesproxies are anonymous




A:τ

B:τ'

C:τ"

θ

A:τ A:τ A:τ

“receive(x), receive(y) occur

in the same ordereverywhere”


Constraint Formalisms


A:τ

τ=(I,O,Pτ,Rτ)

Pτ=

X: φX

Y: φY

Z: φZ

formula in X

formula in Y

formula in Z

PÞP' iff "X φX Þ φ'X(X)

constraints expressed in different formalisms

point-wise comparison

logical consequence in formalism “X”




A:τ

τ=(I,O,Pτ,Rτ)

Pτ=

X: φX

Y: φY

Z: φZ

formula in X

formula in Y

formula in Z








A:τ

τ=(I,O,Pτ,Rτ)

Pτ=X: φX

formula in X

Xparse(I,O,φX:string)

liveobjectsruntimeenvironment

C:ConstraintX1

2

n compare(C, C')

pluggable module “X”




A:τ

τ=(I,O,Pτ,Rτ)

Pτ=X: φX

formula in X



C:ConstraintX1

2

n compare(C, C')




Authentication


Authentication


A:τ

θ=(E,Pθ,Rθ)

X: βX says φX

formula in X

type of the object that must assert it

Pθ=

PÞP' iff "X βX β'X ˄ φX Þ φ'X(X)

additionalrequirement


Authentication



2

3

says XML φX

verify(…, φX)

ok

createproxy

infer type1

XML :θ

4 θ said φX



Demo



http://liveobjects.cs.cornell.edu