Systems Supporting Distributed Collaboration

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Systems Supporting Distributed Collaboration
Prasun Dewan
Department of Computer Science University of
North Carolina CB 3175 Sitterson Hall Chapel
Hill, NC 27599-3175 dewan_at_cs.unc.edu http/www.c
s.unc.edu/dewan
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Definition

• Oxford Work jointly esp at literary or artistic
  production
• Malone helps people work together more
  effectively
• Lynch et al makes users aware they are part of a
  group
• Wells software and hardware for shared
  interactive environment
• Ellis supports groups engaged in a common task
  and provides an interface to shared environment
• Peter Johnson-Lenz computer-mediated culture,
  intentional group processes plus supporting
  software
• Johansen specialized computer aids for
  collaborative work groups
• Winograd state of mind

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Definition
Collaborative Application

• Same output?
• Symmetric?
• N-User?

I/O
I/O
Coupling
User 2
User 1
Potentially Real-Time
4
Traditional Collaborative Applications
File
Mail
Talk
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Benefits Towards Being There
Face-to-Face
Interaction
Computer-Supported
Interaction
Network
6
Gesture Cam Remote Surrogate
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Benefits Beyond Being There
Face-to-Face
Hollan Stornetta 92
Interaction
Computer-Supported
Interaction
Network
8
Action Workflow
Status By Candidate Workflow Step
Manage Review
Manager
Director
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Combining Both Goals?

• IM
• Feel transported to a common abstract world
• Can specify mood
• Collaborative nanoManipulator

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Collaboration vs. Virtual Environments
VE
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Collaboration vs. Real-Time Distributed Apps.
Collaborative Applications
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Collaboration vs. Mobile Apps.
Mobile Applications
Collaborative Applications
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Relationship with Object-Oriented and User
Interface- Technology
Interactive Applications
O-O Applications
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Traditional System Aspects
Applications
Shared Screen
FC vs. CC
Interoperability
Extensibility/Composability
Applications
Telepointer Jitter
Performance/Resource Management
Functionality/Abstraction
Coupling
System Support
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Views of Collaboration Systems

• Ensure actual needs met.
• Conceptual depth, avoid duplication.
• Build on existing knowledge.
• See integrated sets of features

• Problems
• Issues
• Disciplines
• Systems
• Applications and Infrastructures

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Problems Application Areas

• Business Management
• National Collaboratory
• Software Engineering
• Engineering/Design
• Writing

• Decision making, business processes, monitor
  state.
• Connected labs.
• Team development, pair programming
• Just in time VR-based
• Distributed co-authoring.

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Problems Application Areas

• Education
• Medicine
• Air Traffic Control
• Command and Control
• Games/Casual Interaction
• Any complex task!

• Distance presentation, remote lab., colab
  projects
• Remote consult, workflow
• Coordinate controllers
• Coordination
• Sharing of information/actions
• Is collaborative

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Generic Tasks

• Social Interaction
• Information Exchange
• Presentation
• Consulting
• Comment/Discuss
• Compose Artifact

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Generic Tasks Product Life Cycle

• Design
• Implementation
• Debugging/Testing
• Inspection/Review

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Specific Experimental Tasks

• Annotate/discuss research article/software
  specs/video
• Present lecture to remote and local audience
• Rank job candidates
• Choose videos to rent, take on road trip
• Get status report on action items and feedback
  from each participant
• Choose name for new game
• Search for shopping list online

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Views of Collaboration Systems

• Problems
• Issues
• Disciplines
• Systems Applications and Infrastructures

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Issues Semantics

• Session Management How do distributed users
  create, destroy, join, and leave collaborative
  sessions?
• Single-User Interface What are the application
  semantics if there is a single user in the
  session?
• Coupling what feedback does a user receive in
  response to the input of another user?
• Access Control How do we ensure that users do
  not execute unauthorized commands?
• Concurrency Control How do we ensure that
  concurrent users do not enter inconsistent
  commands?

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Issues Semantics (Contd.)

• Process Control How do we ensure that users
  follow prescribed group processes?
• Merging How do we merge concurrent commands
  entered by different users?
• Undo/Redo What are the semantics of undo/redo
  in a collaborative session?
• Awareness How are users made aware of out of
  band'' activities of their collaborator?

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Issues Implementation

• Objects What kind of objects are composed in a
  collaborative application?
• Collaboration Awareness Which of these objects
  are collaboration aware and how are these objects
  integrated with existing, collaboration-unaware
  objects?
• Layers How are these objects arranged in
  layers?
• Concurrency How is the application decomposed
  into concurrent threads?
• Distribution How are the application objects
  placed in different address spaces and hosts?

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Issues Implementation (Contd.)

• Replication/Migration Which of these objects
  are centralized and which are replicated? Which
  of the centralized objects can migrate?
• Display Consistency How to ensure actions are
  executed in the same order on computers that
  share them?
• Real-Time Support What kind of services are
  provided to ensure real-time interaction with
  tolerable jitter and latency?

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Views of Collaboration Systems

• Problems
• Issues
• Disciplines
• Systems Applications and Infrastructures

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Computer Science Disciplines

• Operating Systems
• Database Management Systems
• Programming Languages
• User Interface Systems
• Software Engineering

• Distributed file, memory, scheduling, OS-based
  IM
• Concurrency Control, Recovery
• Shared object constructs
• I/O distribution of window systems, toolkits
• Application area, process control, patterns

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Views of Collaboration Systems

• Problems
• Issues
• Disciplines
• Systems Applications and Infrastructures

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Systems Applications

• RTCALendering
• Cognoter whiteboard
• CES (Transaction-based Collaborative Editing
  System)
• Grove Outline Editor
• Information Lens Typed Email
• Coordinator Speech-Act Workflow
• Quilt Editor Annotations
• IBIS Discussions
• Video Walls
• Hydra
• GroupDraw optimistic CC
• PREP Diff-based Editor
• MUDs (Multiuser Dungeons)
• DIVE (Distributed Interactive
• Virtual Environment)/ MASSIVE

• MIT (Sarin Greif)
• Xerox (Stefik et al)
• MIT (Liskov)
• MCC (Ellis)
• MIT (Malone )
• Stanford (Winograd 88)
• Bellcore (Leland)
• MCC (Ellis)
• Xerox (Abel)
• U. Toronto (Buxton)
• U. Calgary (Greenberg)
• CMU (Neuwirth)
• Xerox (Curtis)
• Sweden (Fahlen)/ Nottingham (Benford)

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Applications Products

• Groove Apps
• OneNote
• Spreadsheet
• Word Processor
• IM

• Microsoft
• Microsoft
• Google
• Google/Writely
• Everyone

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Systems Infrastructures

• NLS (Engelbart 68)
• Colab (Stefik 85)
• VConf (Lantz 86)
• Rapport (Ahuja 89)
• XTV (Abdel-Wahab, Jeffay Feit 91)
• Rendezvous (Patterson 90)
• Suite (Dewan Choudhary 92)
• TeamWorkstation (Ishii 92)
• Weasel (Graham 95)
• Habanero (Chabert et al 98)
• JCE (Abdel-Wahab 99)
• Disciple (Marsic 01)
• Sync (Munson Dewan 96)
• App-Sharer (Chung, Junuzovic, Dewan 06)

• Post Xerox
• Xerox
• Stanford
• Bell Labs
• UNC/ODU
• Bellcore
• Purdue
• Japan
• Queens
• U. Illinois
• ODU
• Rutgers
• UNC

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Infrastructure Products

• VNC (Li, Stafford-Fraser, Hopper 01)
• NetMeeting (MSFT)
• Groove (MSFT)
• Advanced Reality
• LiveMeeting -Pay by minute service model (MSFT)
• Webex (service model)
• MeetingPlace (Cisco)
• CollaborateNow (IBM)

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Multiple Views
Coupling
Cognoter
WYSIWIS Interaction
Database Transactions
NetMeeting
Software Engineering
Design
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Course Goals

• Study State-of-the-art
• Applications
• Shared Word, Browser
• Infrastructure
• Groove, Shared Objects
• Project
• Survey
• Writing
• Integrate with Survey Paper
• Programming
• Integrate with 243/Program Product
• Presentation
• Research
• Assignments
• Using applications and infrastructures
  collaboratively

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Projects

• Infrastructure-based
• Application-/usage- based
• Something usable as this area is
• Practical (probably)
• Unexplored
• Build on top of existing infrastructure
• Sync
• Asynchronous and synchronous
• Application Sharer
• Synchronous existing and new applications

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Application-based

• Make familiar apps collaborative
• Microsoft Office
• Open Office
• Basics implemented
• Make it really work, efficiently
• Eclipse
• Jazz provides some asynchronous support
• Sangam some synchronous support
• Can provide semi-synchronous support
• Loosely coupled pair programming
• Probably remain a prototype

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Application-based

• Custom application for data shared through
  Wikis/Google spreadsheet
• Shared shopping list
• Recreation activities
• Organizing pot-luck parties (custom Evite)
• Departmental activities
• Organizing study groups
• Scheduling departmental picnics
• Signup sheet for demos in 242
• Creating groups in 790-063

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Application-based

• Teaching and TA Award
• Currently nominations requested and then some
  magic happens.
• Allow entry of data and voting and linking of
  teaching evaluations and other data.
• Departmental calendar
• Every week mail sent to coordinator by a certain
  time.
• Calendar emailed and updated by a central person.
• Make this distributed and allow people to enter
  data way in advance.
• Same with Systems Tea

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Application-based

• Qual scheduler
• Automatic did not work.
• Semi-automatic, collaborative.
• Students enter courses and time constraints
• Faculty members enter expertise and time
  constraints
• Schedulers form committees and assign times
  based.
• System checks qual constraints met.
• TA/RA Matcher
• Students and faculty enter preferences.
• Administrators can see all data.
• Students and faculty can see filtered data.
• E.g. one on one matches.

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Application-based

• Undergrad Advising
• filling a form.
• Looking up requirements
• Scheduling a meeting
• Some initial work done by a 145 team

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Infrastructure-based

• Shared layer
• VNC and NetMeeting share different user-interface
  layers
• Benefits of different sharing different layers.
• Can we dynamically change shared layer?
• Dynamic policies, performance model
• Work on application sharer

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Infrastructure-based

• Scheduling
• Feedback vs. Feedthrough processing
• Give sufficient time to both using proportional
  scheduling.
• Energy-aware collaboration
• Energy dissipation a function of amount and rate
  of information communication
• Can study and adjust the coupling (send summary
  information in batches)

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Infrastructure-based

• Locking
• Many locking schemes
• Lock whole spreadsheet vs. individual cell.
• Provide one comprehensive mechanism.
• Partly designed but not implemented.
• Lock-free Consistency management
• Locking ensures displays are consistent no race
  conditions.
• Consistency without locks operation
  transformation
• Called optimistic CC misnomer
• For the mathematically inclined

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Infrastructure-based

• Context-specific presence
• Can synchronously monitor idle time.
• Can synchronously monitor every input in shared
  apps.
• Synchronously summarize application-specific
  information
• E.g. whose mail are you reading?
• Access control
• Needed because we collaborate
• But it is a pain
• Let us collaborate on setting access control.
• An implementation exists
• User studies

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Example collaborative application
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Example collaborative application
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Example collaborative application
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Example collaborative application
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Example collaborative application
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Implementation Alternatives

• Collaboration-unaware apps
• Screen/window (Application) sharing
• Based on existing UI architectures
• App sharing system is collaboration-aware
• ???
• Based on other, ideally popular architectures
• Maybe based on some other cola-aware
  infrastructure
• Collaboration-aware apps
• Based on some architecture or collaboration-aware
  infrastructure

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Does App Sharing work?
Different Window Sizes, Data
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Implementation Alternatives

• Collaboration-unaware apps
• Screen/window (Application) sharing
• Based on existing UI architectures
• App sharing system is collaboration-aware
• ???
• Based on other, ideally popular architectures
• Maybe based on some other colab-aware
  infrastructure
• Collaboration-aware apps
• Based on some architecture or collaboration-aware
  infrastructure

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Model, View and Controller (MVC)
View
Controller
Model
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Model, View and Controller (MVC)
Controller
View
Model
View
Controller
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Model Code

• public class ConcertExpense
• float unitCost 0
• int numberOfAttendees 0
• PropertyChangeSupport propertyChange
  new PropertyChangeSupport(this)
• public float getTicketPrice() return
  unitCost
• public void setTicketPrice(float newVal)
  
• if (newVal unitCost) return
• float oldVal unitCost int oldTotal
  getTotal()
• unitCost newVal
• propertyChange.firePropertyChange("ticket
  Price", oldVal, newVal)
• propertyChange.firePropertyChange("total"
  , oldTotal, getTotal())
• public int getNumberOfAttendees()
  return numberOfAttendees
• public void setNumberOfAttendees(int
  newVal)
• if (numberOfAtendees newVal) return
• int oldVal numberOfAttendees int oldTotal
  getTotal()
• numberOfAttendees newVal
  propertyChange.firePropertyChange("numberOfAttend
  ees", oldVal, newVal)
• propertyChange.firePropertyChange("total"
  , oldTotal, getTotal())

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MVC Composition

• package main
• import budget.ConcertExpense
• import bus.uigen.ObjectEditor
• public class MVCBudget
• public static void main(String args)
• ConcertExpense model new ConcertExpense ()
• ObjectEditor.edit(model)

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Distributed MVC
Controller
View
Model
View
Controller
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DistributedModel Code

• public class ConcertExpense extends
  UnicastRemoteObject implements Remote
• float unitCost 0
• int numberOfAttendees 0
• RemotePropertyChangeSupport
  propertyChange new RemotePropertyChangeSupport(t
  his)
• public float getTicketPrice() throws
  RemoteException return unitCost
• public void setTicketPrice(float newVal)
  
• unitCost newVal
• propertyChange.firePropertyChange("ticket
  Price", null, newVal)
• propertyChange.firePropertyChange("total"
  , null, getTotal())
• public int getNumberOfAttendees() throws
  RemoteException return numberOfAttendees
• public void setNumberOfAttendees (int
  newVal) throws RemoteException
• numberOfAttendees newVal
• propertyChange.firePropertyChange("number
  OfAttendees", null, newVal)
• propertyChange.firePropertyChange("total"
  , null, getTotal())
• public float getTotal() throws
  RemoteException return unitCostnumberOfAttendees
  
• public void addRemotePropertyChangeListene
  r(RemotePropertyChangeListener l) throws
  RemoteException
• propertyChange.addRemotePropertyChange
  Listener(l)

Distribution-Aware
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Notification

• public interface PropertyChangeListener
• public void propertyChange(PropertyChangeEve
  nt evt)

Does not extend Remote
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Remote Notification
package util import java.beans.PropertyChangeEven
t import java.rmi.Remote import
java.rmi.RemoteException public interface
RemotePropertyChangeListener extends Remote
public void remotePropertyChange(PropertyChange
Event evt) throws RemoteException
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Registering a Model

• import java.rmi.Naming
• public class AConcertExpenseRegisterer
• public final static String RMI_PORT 1099
  // default port for RMI service
• public final static MODEL_NAME
  myDemoBudget
• public static void main (String args)
• try
• String host_name
• java.net.InetAddress.getLocalHost().getCanonica
  lHostName()
• ConcertExpense model new ConcertExpense()
• String budgetName "//" host_name ""
  RMI_PORT "/" MODEL_NAME
• Naming.rebind(budget_name, model)
• catch (Exception e)
• e.printStackTrace()

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Looking up a Model

• import java.rmi.Naming
• import bus.uigen.ObjectEditor
• public class AConcertExpenseComposer
• final static String REMOTE_HOST
  dewan-cs.cs.unc.edu
• final static FULL_MODEL_NAME //"
  REMOTE_HOST "" AConcerExpenseRegisterer.RM
  I_PORT "/" AConcertExpenseRegisterer.MODEL_
  NAME
• public static void main (String args)
• try
• ConcertExpense model (ConcertExpense)
  Naming.lookup(MODEL_NAME)
• // connect to generic model and view
• ObjectEditor.edit(model)
• catch (Exception e)
• e.printStackTrace()

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Compile Runtime steps

• Compile steps
• rmic budget.ConcertExpense
• Runtime steps
• Start rmi service
• set CLASSPATHltmodel, stubs, skel directorygt
• rmiregistry 1099
• Start registerer
• Start composer at each users workstation

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Screen Sharing vs. MVC Sharing
Data convergence after each user command
WYSIWIS
66
Transactions/Disconnection
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Transactions/Disconnection
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Concurrent Transactions
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Concurrent Transactions
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Concurrent Transactions
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Concurrent Transactions
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Concurrent Transactions
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Concurrent Transactions
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Concurrent Transactions
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Conflicting Transactions
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Conflicting Transactions
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Conflicting Transactions
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Conflicting Transactions
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Overriding Transactions
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Overriding Transactions
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Private Data
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Minimum Goals

• Model and not View Sharing
• Logical Disconnection
• Asynchronous Connected Transactions
• Disconnected Transactions
• Conflict resolution
• Awareness of collaborators
• Private Data

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Distributed MVC
Controller
View
Model
View
Controller
84
Replicated MVC
Controller
View
Model
Model-View Communication same as Model-Model
Communication?
Model
View
Controller
85
Distributed MVC
Controller
View
Model

• Equivalent to Centralized
• Performance difference
• May change dynamically

View
Controller
86
Replicated MVC
Controller
View
Model
Both users create replicas?
Model
View
Controller
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Disconnected Interaction
Controller
View
Model
88
Need Replicating Infrastructure
Controller
View
Model
Binds to Local (Possibly Different)
View/Controller
Serializes Model
Infrastructure
89
Need Replicating Infrastructure
Controller
View
Model
Client Part
Server Part
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Original Model Code

• public class ConcertExpense
• float unitCost 0
• int numberOfAttendees 0
• PropertyChangeSupport propertyChange
  new PropertyChangeSupport(this)
• public float getTicketPrice() return
  unitCost
• public void setTicketPrice(float newVal)
  
• if (newVal unitCost) return
• float oldVal unitCost int oldTotal
  getTotal()
• unitCost newVal
• propertyChange.firePropertyChange("ticket
  Price", oldVal, newVal)
• propertyChange.firePropertyChange("total"
  , oldTotal, getTotal())
• public int getNumberOfAttendees()
  return numberOfAttendees
• public void setNumberOfAttendees(int
  newVal)
• if (numberOfAtendees newVal) return
• int oldVal numberOfAttendees int oldTotal
  getTotal()
• numberOfAttendees newVal
  propertyChange.firePropertyChange("numberOfAttend
  ees", oldVal, newVal)
• propertyChange.firePropertyChange("total"
  , oldTotal, getTotal())

Requires use of standard notification mechanism
so local infrastructure can listen
91
Replicated Model Code

• public class ConcertExpense implements
  Serializable
• float unitCost 0
• int numberOfAttendees 0
• transient PropertyChangeSupport
  propertyChange new PropertyChangeSupport(this)
  
• public float getTicketPrice() return
  unitCost
• public void setTicketPrice(float newVal)
  
• if (newVal unitCost) return
• float oldVal unitCost int oldTotal
  getTotal()
• unitCost newVal
• propertyChange.firePropertyChange("ticket
  Price", null, newVal)
• propertyChange.firePropertyChange("total"
  , null, getTotal())
• public int getNumberOfAttendees()
  return numberOfAttendees
• public void setNumberOfAttendees(int
  newVal)
• if (numberOfAtendees newVal) return
• int oldVal numberOfAttendees int oldTotal
  getTotal()
• numberOfAttendees newVal
• propertyChange.firePropertyChange("number
  OfAttendees", null, newVal)
• propertyChange.firePropertyChange("total"
  , null, getTotal())

Transient variables null in serialized object
No cycles should be created by non-transient
links
92
Replicated Model Code

• public class ConcertExpense implements
  Serializable
• float unitCost 0
• int numberOfAttendees 0
• transient PropertyChangeSupport
  propertyChange new PropertyChangeSupport(this)
  
• public float getTicketPrice() return
  unitCost
• public void setTicketPrice(float newVal)
  
• if (newVal unitCost) return
• float oldVal unitCost int oldTotal
  getTotal()
• unitCost newVal
• propertyChange.firePropertyChange("ticket
  Price", null, newVal)
• propertyChange.firePropertyChange("total"
  , null, getTotal())
• public int getNumberOfAttendees()
  return numberOfAttendees
• public void setNumberOfAttendees(int
  newVal)
• if (numberOfAtendees newVal) return
• int oldVal numberOfAttendees int oldTotal
  getTotal()
• numberOfAttendees newVal
• propertyChange.firePropertyChange("number
  OfAttendees", null, newVal)
• propertyChange.firePropertyChange("total"
  , null, getTotal())

Method with well known signature called by
Infrastructure on serialized object
93
Fine-Grained Merging

• Objects are encapsulated.
• How to break state into units
• To read incremental state
• Set incremental state
• Serializing copies complete object
• Use Bean Programming Patterns and Property
  Notifications

94
MVC Composition

• package main
• import budget.ConcertExpense
• import bus.uigen.ObjectEditor
• public class MVCBudget
• public static void main(String args)
• ConcertExpense model new ConcertExpense ()
• ObjectEditor.edit(model)

95
Registering and composing

• package main
• import budget.ConcertExpense
• import edu.unc.sync.Sync
• public class SyncBudgetCreator
• public static String SERVER_NAME
  "dewan-cs.cs.unc.edu/A"
• public static String MODEL_NAME "demoBudget"
• public static String CLIENT_ID "alice"
• public static void main(String args)
• ConcertExpense model new ConcertExpense ()
• Sync.replicate (SERVER_NAME,
• MODEL_NAME,
• model,
• CLIENT_ID)
• ObjectEditor.edit(model)

96
Looking up and composing
Special program needed for creator

• package main
• import budget.ConcertExpense
• import edu.unc.sync.Sync
• import edu.unc.sync.server.SyncClient
• import edu.unc.sync.server.ServerProxy
• public class SyncBudgetUser
• static String CLIENT_ID bob"
• public static void main(String args)
• SyncClient client Sync.open
  (SyncBudgetCreator.SERVER_NAME,
• SyncBudgetAlice.MODEL_NAME,
• CLIENT_ID)
• ServerProxy server client.getServerProxy(SyncB
  udgetCreator.SERVER_NAME)
• ConcertExpense model (ConcertExpense)
  server.getModel
• (SyncBudgetCreator.MODEL_NAME)
• ObjectEditor.edit(model)

97
Symmetric Programs

• System can create new model only if it does not
  exist.
• It can be given model class instead of model
  instance

98
Maybe Registering and composing

• package main
• import budget.ConcertExpense
• import edu.unc.sync.Sync
• import edu.unc.sync.SyncClient
• import edu.unc.sync.SyncProxy
• public class SyncBudget
• public static String SERVER_NAME
  "dewan-cs.cs.unc.edu/A"
• public static String MODEL_NAME "demoBudget"
• public static Class MODEL_CLASS
  ConcertExpense.class
• public static void main(String args)
• SyncClient client Sync.replicate
  (SERVER_NAME, MODEL_NAME,
• MODEL_CLASS, args0)
• ServerProxy server client.getServerProxy(SERVE
  R_NAME)
• ConcertExpense model (ConcertExpense)
  server.getModel (MODEL_NAME)
• ObjectEditor.edit(model)

99
Infrastructure-defined Model-View Interface

• If Infrastructure defines model-view interface
• It can create model and view
• It can compose them

100
Automatic Creation of MVC Structure

• package main
• import budget.ConcertExpense
• import edu.unc.sync.SyncObjectEditor
• import edu.unc.sync.Sync
• public class SyncBudget
• public static String SERVER_NAME
  "dewan-cs.cs.unc.edu/A"
• public static String MODEL_NAME "demoBudget"
• public static Class MODEL_CLASS
  ConcertExpense.class
• public static Class EDITOR_CLASS
  SyncObjectEditor.class
• public static void main(String args)
• Sync.replicate (SERVER_NAME, MODEL_NAME,
• 
  MODEL_CLASS, EDITOR_CLASS, args0)

Can execute this interactively!
101
View Interfaces

• package edu.unc.sync.server
• import edu.unc.sync.Replicated
• public interface SyncApplication
• public void init(Object invoker) // invoker
  is sync client or server
• public void addObject(Replicated object,
  String name) // replicated is what model gets
  converted to
• public void addObject(Object object, String
  name)
• public void doRefresh() // Sync calls this
  whenever it updates model in case app does not
  listen to events

102
Automatic Creation of MVC Structure

• package main
• import budget.ConcertExpense
• import edu.unc.sync.SyncObjectEditor
• import edu.unc.sync.Sync
• public class SyncBudget
• public static String SERVER_NAME
  "dewan-cs.cs.unc.edu/A"
• public static String MODEL_NAME "demoBudget"
• public static Class MODEL_CLASS
  ConcertExpense.class
• public static Class EDITOR_CLASS
  SyncObjectEditor.class
• public static void main(String args)
• Sync.replicate (SERVER_NAME, MODEL_NAME,
• 
  MODEL_CLASS, EDITOR_CLASS, args0)

Constructors with parameters?
103
Constructors with Parameters

• Dont have them
• Use init method.
• Application knows what parameters to give.
• Infrastructure knows when and if to create
  instance.
• Application gives factory.
• For any model or editor class

104
Automatic Creation of MVC Structure

• package main
• import budget.ConcertExpense
• import edu.unc.sync.SyncObjectEditor
• import edu.unc.sync.Sync
• public class SyncBudget
• public static String SERVER_NAME
  "dewan-cs.cs.unc.edu/A"
• public static String MODEL_NAME "demoBudget"
• public static Class MODEL_CLASS
  ConcertExpense.class
• public static Class EDITOR_CLASS
  SyncObjectEditor.class
• public static void main(String args)
• Sync.register(ConcertExpense.class, new
  ConcertExpenseFactory())
• Sync.replicate (SERVER_NAME, MODEL_NAME,
• 
  MODEL_CLASS, EDITOR_CLASS, args0)

105
Factory Interfaces
package edu.unc.sync public interface
ObjectFactory public Object newInstance(Class
c)

• import budget.ConcertExpense
• import edu.unc.sync.ObjectFactory
• public class ConcertExpenseFactory implements
  ObjectFactory
• public Object newInstance (Class c)
• return new ConcertExpense()

106
Multiple Models

• package main
• import budget.ConcertExpense
• import edu.unc.sync.SyncObjectEditor
• import edu.unc.sync.Sync
• import edu.unc.sync.SyncClient
• import edu.unc.sync.SyncProxy
• public class SyncBudget
• public static String SERVER_NAME
  "dewan-cs.cs.unc.edu/A"
• public static String MODEL_NAME "demoBudget"
• public static String MODEL_NAME_2
  "demoBudget2"
• public static Class MODEL_CLASS
  ConcertExpense.class
• public static Class EDITOR_CLASS
  SyncObjectEditor.class
• public static void main(String args)
• SyncClient client Sync.replicate
  (SERVER_NAME, MODEL_NAME,
• 
  MODEL_CLASS, EDITOR_CLASS, args0)
• ServerProxy server client.getServerProxy(SERVE
  R_NAME)
• server.newObject(MODEL_NAME_2,
  ConcertExpense.class, EDITOR_CLASS)

107
Replicated Model Code

• public class ConcertExpense implements
  Serializable
• float unitCost 0
• int numberOfAttendees 0
• transient PropertyChangeSupport
  propertyChange new PropertyChangeSupport(this)
  
• public float getTicketPrice() return
  unitCost
• public void setTicketPrice(float newVal)
  
• if (newVal unitCost) return
• float oldVal unitCost int oldTotal
  getTotal()
• unitCost newVal
• propertyChange.firePropertyChange("ticket
  Price", null, newVal)
• propertyChange.firePropertyChange("total"
  , null, getTotal())
• public int getNumberOfAttendees()
  return numberOfAttendees
• public void setNumberOfAttendees(int
  newVal)
• if (numberOfAtendees newVal) return
• int oldVal numberOfAttendees int oldTotal
  getTotal()
• numberOfAttendees newVal
• propertyChange.firePropertyChange("number
  OfAttendees", null, newVal)
• propertyChange.firePropertyChange("total"
  , null, getTotal())

No cycles created by non-transient links
108
Supporting Private Data?
109
Unshared Property

• public class ConcertExpenseWithAttendance extends
  ConcertExpense
• boolean attend
• public boolean getWillAttend()
• return attend
• public void setWillAttend(boolean newVal)
  
• if (attend newVal) return
• attend newVal
• if (newVal)
• setNumberOfAttendees (getNumberOfAttende
  es() 1)
• else
• setNumberOfAttendees (getNumberOfAttende
  es() - 1)

Infrastructure not told about change to
willAttend property
Can use two different notification models. Or use
special API
Neither is View!
110
Selective Replication

• package main
• import budget.ConcertExpense
• import edu.unc.sync.SyncObjectEditor
• import edu.unc.sync.Sync
• public class SyncBudget
• public static String SERVER_NAME
  "dewan-cs.cs.unc.edu/A"
• public static String MODEL_NAME "demoBudget"
• public static Class MODEL_CLASS
  ConcertExpenseWithAttendance.class
• public static Class EDITOR_CLASS
  SyncObjectEditor.class
• public static void main(String args)
• // can also choose if replicate in or out
• Sync.setReplicate(ConcertExpenseWithAttendance.c
  lass, willAttend", false)
• Sync.replicate (SERVER_NAME, MODEL_NAME,
• MODEL_CLASS,
  EDITOR_CLASS, args0)

111
Awareness Controlling Synchronization
112
Awareness Controlling Synchronization

• package main
• import budget.ConcertExpense
• import edu.unc.sync.SyncObjectEditor
• import edu.unc.sync.Sync
• import edu.unc.sync.SyncClient
• public class SyncBudget
• public static String SERVER_NAME
  "dewan-cs.cs.unc.edu/A"
• public static String MODEL_NAME "demoBudget"
• public static Class MODEL_CLASS
  ConcertExpenseWithAttendance.class
• public static Class EDITOR_CLASS
  SyncObjectEditor.class
• public static void main(String args)
• SyncClient client Sync.replicate
  (SERVER_NAME, MODEL_NAME,
• MODEL_CLASS,
  EDITOR_CLASS, args0)
• ObjectEditor.edit (new SyncControls(client.getSe
  rverProxy(SERVER_NAME))

113
Sync Controls

• package budget
• import java.beans.PropertyChangeListener
• import java.beans.PropertyChangeSupport
• import java.util.Observable
• import java.util.Observer
• import java.util.Vector
• import edu.unc.sync.server.ServerProxy
• public class SyncControls extends Observable
  implements Observer
• PropertyChangeSupport propertyChange new
  PropertyChangeSupport(this)
• ServerProxy server
• public SyncControls (ServerProxy theServer)
• server theServer
• server.addObserver(this)
• public boolean getRealTimeSynchronize()
• return server.getRealTimeSynchronize()
• public void setRealTimeSynchronize (boolean
  newVal)
• server.setRealTimeSynchronize(newVal)

114
Sync Controls (contd.)

• public Vector getCurrentCollaborators()
• return server.getOtherClientNames()
• public void synchronize()
• server.synchronize()
• public void addPropertyChangeListener(PropertyCha
  ngeListener l)
• propertyChange.addPropertyChangeListener(
  l)
• public void notifyObservers (Object arg)
• setChanged()
• super.notifyObservers(arg)
• public void update (Observable observable,
  Object event )
• notifyObservers(event)

115
Does this work?

• public class ConcertExpenseWithAttendance extends
  ConcertExpense
• boolean attend
• public boolean getWillAttend()
• return attend
• public void setWillAttend(boolean newVal)
  
• if (attend newVal) return
• attend newVal
• if (newVal)
• setNumberOfAttendees (getNumberOfAttende
  es() 1)
• else
• setNumberOfAttendees (getNumberOfAttende
  es() - 1)

116
Concurrent Transactions
117
Concurrent Transactions
118
Concurrent Transactions
119
Concurrent Transactions
120
Concurrent Transactions
121
Concurrent Transactions
Race condition!
122
Does this work?

• public class ConcertExpenseWithAttendance extends
  ConcertExpense
• boolean attend
• public boolean getWillAttend()
• return attend
• public void setWillAttend(boolean newVal)
  
• if (attend newVal) return
• attend newVal
• if (newVal)
• setNumberOfAttendees (getNumberOfAttende
  es() 1)
• else
• setNumberOfAttendees (getNumberOfAttende
  es() - 1)

Does not keep track of who is attending. Event
vs. state-based
123
Bean Properties vs. Records

• Previous solution requires table mapping users to
  attendance
• Bean properties define replicated records
• No notifications needed if property object does
  not change
• Though its components may.
• Currently need to define getter and setter for
  each shared property
• Other important concrete types
• Dynamic Sequences
• Hashtables
• Want arbitrary compositions of records,
  sequences, and tables

124
Inheritance Based Approach

• Create predefined replicated hashtable and vector
• ReplicatedSequence
• ReplicatedHashtable
• Can subclass to add functionality
• Sequence user
• is-a sequence
• has-a sequence

125
Inheritance Based Approach

• public class ReplicatedDirectory extends
  ReplicatedDictionary implements FileWrapper
• public Replicated remove(Object key)
• Replicated value super.remove(key)
• if (value instanceof FileWrapper)
• File file ((FileWrapper)
  value).getFile()
• if (file.exists() !delete(file))
  toBeDeleted.addElement(file)
• return value

126
Hashtable Pattern

• import bus.uigen.HashtableChangeSupport
• import bus.uigen.HashtableListener
• public class AConcertExpenseTable implements
  java.io.Serializable
• String name ""
• HashtableltString, ConcertExpensegt table new
  Hashtable()
• public Enumeration keys ()
• return table.keys()
• public Enumeration elements ()
• return table.elements()
• public void put (String key, String
  ConcertExpense)
• table.put(key, value)
• hashtableChangeSupport.keyPut(key, value)
• public ConcertExpense remove (String key)
• ConcertExpense retVal table.remove(key)
• hashtableChangeSupport.keyRemoved(key)
• return retVal

Arbitrary type
127
Hashtable Events

• HashtableChangeSupport hashtableChangeSupport
  new HashtableChangeSupport(this)
• public void addHashtableListener
  (HashtableListener hashtableListener)
• hashtableChangeSupport.addHashtableListener(hash
  tableListener)
• public void removeHashtableListener(HashtableList
  ener hashtableListener)
• hashtableChangeSupport.removeHashtableListener(h
  ashtableListener)

128
Hashtable Listener Interface

• // dont really need to worry about this unless
  implementing custom UI
• package bus.uigen
• public interface HashtableListener
• public void keyPut(Object key, Object value,
  int newSize)
• public void keyRemoved(Object key, int newSize)
  

129
Vector Pattern

• import bus.uigen.VectorChangeSupport
• import bus.uigen.VectorMethodsListener
• import bus.uigen.VectorListener
• public class AnOutline implements
  java.io.Serializable
• Vector contents new Vector()
• //non pattern method
• public void addString() addElement("")
• //non pattern method for creating recursive
  structure
• public void addOutline() addElement (new
  AnOutline())
• // either this read method
• public Enumeration elements () return
  contents.elements()
• //or this pair
• public int size() return contents.size()
• public Object elementAt() return
  contents.elementAt()

Programmer-defined
130
Vector Pattern

• // optional
• public void addElement(Object element)
• contents.addElement(element)
• vectorChangeSupport.elementAdded(element)
• //optional
• public void removeElement(Object element)
• contents.removeElement(element)
• vectorChangeSupport.elementRemoved(element)
• //optional
• public void setElementAt(Object element, int
  index)
• System.out.println("AnOutline" element
  "at" index)
• contents.setElementAt(element, index)
• vectorChangeSupport.elementChanged(element,
  index)
• //optional

131
Vector Events

• VectorChangeSupport vectorChangeSupport new
  VectorChangeSupport(this)
• // the following two needed for Sync
• public void addVectorMethodsListener(VectorMethod
  sListener vectorListener)
• vectorChangeSupport.addVectorMethodsListener(vec
  torListener)
• public void removeVectorMethodsListener(VectorMet
  hodsListener vectorListener)
• vectorChangeSupport.removeVectorMethodsListener(
  vectorListener)
• // the ones below needed for automatic user
  interface generation
• public void addVectorListener(VectorListener
  vectorListener)
• vectorChangeSupport.addVectorListener(vectorList
  ener)
• public void removeVectorListener(VectorListener
  vectorListener)
• vectorChangeSupport.removeVectorListener(vectorL
  istener)

132
VectorMethodsListener

• package bus.uigen
• public interface VectorMethodsListener
• public void elementAdded(Object element, int
  newSize)
• public void elementInserted(Object element, int
  pos, int newSize)
• public void elementChanged(Object element, int
  pos)
• public void elementRemoved(int pos, int
  newSize)
• public void elementRemoved(Object element, int
  newSize)

133
VectorListener

• package bus.uigen
• public interface VectorListener
• public void updateVector(uiVectorEvent evt)

134
VectorEvent

• public class uiVectorEvent implements
  java.io.Serializable
• public static final int AddComponentEvent 1,
• DeleteComponentEvent
  2,
• ChangeComponentEvent
  3,
• InsertComponentEvent 4,
• CompletedComponentsEvent 5,
• UndefEvent 1000
• public int getEventType()
• public Object getNewValue()
• public int getNewSize()
• public Object getOldValue()
• public int getPosition()

135
Three Useful Existing Classes

• bus.uigen.AListenableVector implements
  bus.uigen.VectorInterface
• implements vector pattern and fires appropriate
  events
• bus.uigen.AListenableString implements
  bus.uigen.VectorInterface
• implements the vector pattern with character
  instead of object elements.
• fires vector events as user inserts, deletes,
  characters
• SyncObjectEditor displays it as a text field
• updates it incrementally
• Write method of associated property/sequence/hasht
  able invoked when user hits Enter
• bus.uigen.AListenableHashtable implements
  bus.uigen.HashtableInterface
• implements hashtable pattern and fires
  appropriate events

136
Does this work?

• public class ConcertExpenseWithAttendance extends
  ConcertExpense
• boolean attend
• public boolean getWillAttend()
• return attend
• public void setWillAttend(boolean newVal)
  
• if (attend newVal) return
• attend newVal
• if (newVal)
• setNumberOfAttendees (getNumberOfAttende
  es() 1)
• else
• setNumberOfAttendees (getNumberOfAttende
  es() - 1)

Need table of who is attending.
137
Overcoming Race Conditions

• package budget
• import java.io.Serializable
• import java.util.Enumeration
• import java.beans.PropertyChangeSupport
• import java.beans.PropertyChangeListener
• import bus.uigen.AListenableHashtable
• import bus.uigen.HashtableInterface
• public class ConcertExpenseWithAttendanceTable
  extends ConcertExpense HashtableInterfaceltStri
  ng, Booleangt attendance new AListenableHashtable
  ()
• public HashtableInterface getAttendance()
  return attendance
• public void setAttendance(HashtableInterface
  newVal) attendance newVal
• public int getNumberOfAttendees()
• Enumeration elements attendance.elements()
  
• int retVal 0
• while (elements.hasMoreElements())
  
• if (((Boolean) elements.nextElement()).equals(tr
  ue)) retVal
• return retVal

138
Overcoming Race Conditions

• transient String userName "Anonymous"
• public void initUserName (String initVal)
  
• userName initVal attendance.put(userName
  , attend)
• boolean attend
• public boolean getWillAttend() return
  attend
• public void setWillAttend(boolean newVal)
  
• if (attend newVal) return
• attend newVal
• attendance.put(userName, attend)

139
Attendance Table
140
Attendance Table
141
Attendance Table
142
Patterns Summary

• Record
• Vector
• Hashtable

143
Infrastructure Derivation

• Derived from first principles
• Some Java constraints
• Implemented in Sync
• Presentation influenced Sync design
• Just in time implementation

144
Interfaces vs. Patterns

• Patterns describe a family of interfaces
• Unification done at runtime, as in type inference
• T elementAt (int i), addElement (T newVal)
• T getP(), void setP(T newVal)
• Certain methods are optional
• insertElement() or addElement() can change a
  sequence
• Parameterized interfaces require fixed number of
  methods and have no runtime unification
• Errors in usage caught at compile time.

145
Possible Pattern errors

• May forget to define read or write methods
• E.g. missing setter
• Read and write methods may not unify.
• Write methods may not send events
• Missing or unexpected method for registering
  observers.
• Missing or unexpected initializer of serialized
  objects

146
Possible Serialization Errors

• Object may not be serializable
• Serializable superclass gt Serializable subclass
• Improper use of transient
• Cycles in non-transient variables
• Assigning serialVersionUID a value of 1L.
• Dont know why Eclipse assigns one

147
Summary

• Clients can be started in any order.
• First one run results in object creation.
• Other one gets serialized replica
• View connected by Sync to replica
• SyncObjectEditor is a generic extendible editor
• SyncApplication interface around ObjectEditor
• Can replace it with custom editor implementing
  common interface
• Can create multiple objects in server
• Each model tree converted to an internal tree of
  records, vectors and hashtables in SyncClient
  based on patterns in model tree.
• Events fired from model tree result in updates to
  client tree.
• Client tree synchronized with Server tree when
  synchronize called.
• Synchronize side effect of property handler if in
  realTime mode.
• Model can be changed by programmer.
• Synchronize can be called by programmer.

148
Limits of Replicated

• Records
• Hashtables
• Vectors
• What kinds of apps can be built?

149
Sync Drawer (Munson)

• Shape object to capture coordinates.
• Hashtable for shapes
• Existing single-user app transformed

150
Weather Report (Calandrino)

• Extends SyncObjectEditor
• Users from different locations enter data
• Aggregated by Object

151
Word Processor (Agiwal)

• Hierarchical document
• Text objects have shared properties

152
Word Processor (Porwal)

• Hierarchical Outline
• Can move items

153
Spreadsheet (Luebke)

• Hashtable
• Used existing single-user tool

154
Calendar (McEuen)

• Hashtable
• Used existing single-user tool

155
Chat Application (Karl)
156
Aware Chat (Wiegand)
157
Experimental Data Set (Jordan)

• Scientists collaborating on experimental data

158
Starting the Server
159
Starting the Server
160
Server UI
161
Server Script and java.policy

• set synclib D/dewan_backup/java/lib/syncall.jar
• set CLASSPATHsynclib ltother dirs or jarsgt
• java -classpath CLASSPATH -Djava.security.policy
  synclib/java.policy
• -Djava.util.prefs.syncInterval2000000
  edu.unc.sync.server.SyncServer ui trace
  server_id A

Default port is 1099
162
Java.policy
grant permission java.security.AllPermission

163
RMI Registry Script

• set javabinC\"Program Files"\Java\jre1.5.0_04\bi
  n
• set synclib D/dewan_backup/java/lib/syncall.jar
• set CLASSPATHsynclib ltother dirs or jarsgt
• javabin\rmiregistry 1099

164
Steps

• Install sync jar file
• Install java.policy file
• Runtime
• Start rmiregistry
• Make sure it has the jar file in class path.
• Start Sync server
• Make sure it has the jar file in class path and
  arguments like reference to java.policy
• Start program interacting with SyncClient on
  computer of each interacting user.
• Make sure it has the jar file in class path
• Can do this all on one machine.
• Need to loosen firewall if server on different
  machine
• One same machine, must give unique IDs to clients.

165
Possible Errors and Symptoms

• SyncServer could not be bound at specified port
  access denied (java.net.SocketPermission
  127.0.0.11099 connect,resolve
• rmiregistry not started, Java.policy file not
  installed or not given as server argument
• SyncServer could not be bound at specified port
  RemoteException occurred in server thread nested
  exception is  java.rmi.UnmarshalException error
  unmarshalling arguments nested exception is  
       java.lang.ClassNotFoundException
  edu.unc.sync.server.SyncServer_Stub
• Sync not in class path of rmiregistry
• No user interface created
• -- ui not passed as argument to Sync server
• Could not open dewan-cs.cs.unc.edu/A
• Server not started,
• Client gives wrong id or hostname for server
  (case matters!)
• The user-interfaces not connected
• Unique client IDs not given

166
Possible Errors and Symptoms

• Initial client interfaces same but subsequent
  synchronization does not occur
• Property events not fired
• Explicitly set replicate to false
• Initial user-interfaces different but subsequent
  synchronization of components occurs
• Transient or non-serializable components
• Get null pointer exception when firing events
• Not defined initSeralizedObject() method
• InvalidClass Exception
• private static final long serialVersionUID 1L
• Get rid of the variable declaration or dont
  assign it a value

167
Possible Errors

• Get null server proxy
• May be passing in wrong name
• Or could be an eclipse error
• Call getServerProxy() with no argument
• Returns the first server opened by client
• Get null model from server proxy
• Maybe passing wrong model name
• Call initialModel
• Returns the first model created at proxy
• Get events from AListenableString only sometimes
• Not registering listener of all instances created

168
Sync Client User Interface

• SyncClient is also a main program
• Can be used to connect to servers.
• Add objects to a server

169
Sync Client User Interface
170
Mapping Names to Classes

• objectsReplicated_Directory Text
• Replicated_Directory.classSyncFiles.ReplicatedDir
  ectory
• SyncFiles.ReplicatedDirectory.editorSyncFiles.Fil
  eEditor
• Text.class bus.uigen.AListenableString
• bus.uigen.AListenableString.editorSyncObjectEdito
  r