1. K. Stirewalt CSE 335: Software Design Software architecture and larger system design issues Lecture 1: Simulating concurrency Topics: –High-level software architecture and its impact on the design of classes, roles, and collaborations –Focus: Concurrency

2. K. Stirewalt CSE 335: Software Design Outline of course topics Foundational OO concepts Synthetic concepts: –Program families, program fragments, and abstract classes –Separation of concepts Separating/encapsulating cross-cutting operations [Visitors] Mixin classes Reusable strategies and object-oriented frameworks –Reusable collaborations Software architecture and larger design issues Software process issues

3. K. Stirewalt CSE 335: Software Design Outline of course topics Foundational OO concepts Synthetic concepts Software architecture and larger design issues: –Strategic design decisions that influence a host of smaller, more tactical design decisions E.g., policy for persistence of data in long-running system E.g., allocating functionality to a single, centralized system vs. distributing functionality among a collection of communicating hosts –Often involve a major capital investment –Source of both risk and opportunity –Require lots of a priori modeling and analysis –Focus: Design issues related to concurrent and distributed systems Software process issues

4. K. Stirewalt CSE 335: Software Design Strategic design decisions Defn: High-level design decisions that influence the form of much of the final code –Have dramatic impact on performance, extensiblity, reusability, and/or maintainablity of the final system –Should be made very deliberately Analogy: –Good design yields software assets –Strategic design decisions are major capital investments

5. K. Stirewalt CSE 335: Software Design System design Defn: High-level strategy for solving an information flow problem and building a solution [Blaha & Rumbaugh] –Includes decisions about organization of functionality –Allocation of functions to hardware, software, and people –Other major policy decisions that are prior to technical design Assumes and builds upon a thorough requirements analysis

6. K. Stirewalt CSE 335: Software Design Example system-design decisions Choose system performance constraints Organize system into subsystems Identify concurrency and choose a strategy for implementing concurrent control Choose a policy/mechanisms for managing persistent data Make a reuse plan Etc…

7. K. Stirewalt CSE 335: Software Design Example system-design decisions Choose system performance constraints Organize system into subsystems Identify concurrency and choose a strategy for implementing concurrent control Choose a policy/mechanisms for managing persistent data Make a reuse plan Etc…

8. K. Stirewalt CSE 335: Software Design Example concern: Concurrency Many modern desktop applications perform multiple tasks concurrently Lots of different ways to implement concurrency in an application Each approach comes with its own set of costs and benefits More important: Each approach can have a dramatic impact on how one designs every class in the system

9. K. Stirewalt CSE 335: Software Design Recall design of document browser vp : …sb : …vpm : …dm : … announceNewValue(X) update() retrieve(0,...)getLine(X, …) retrieve(n,...) getLine(X+n, …) … userEvent() announceNewValue(X) sd design3

10. K. Stirewalt CSE 335: Software Design Exercise Suppose we want to replace the DocManager with a StreamManager, which continuously reads lines to display from a service over the network. This manager must notify scrollbar and viewport when a new line is read from network. Task: Draw a sequence diagram that depicts what happens when the stream manager reads a new line from the network.

11. K. Stirewalt CSE 335: Software Design >>

12. K. Stirewalt CSE 335: Software Design Solution sketch vp : …sb : …vpm : …sm : … announceNewValue(X) update() retrieve(0,...)getLine(X, …) retrieve(n,...) getLine(X+n, …) … announceNewValue(X) sd stream serviceNetwork() ???

13. K. Stirewalt CSE 335: Software Design Question Who generates this call to serviceNetwork? Where would we place it in our application code?

14. K. Stirewalt CSE 335: Software Design Design of function main() int main (void) { … StreamManager* sm = new StreamManager( … ); MyScrollBar* sb = new MyScrollBar( … ); MyViewPort* vp = new MyViewPort( … ); MyViewPortModel* vpm = newMyViewPortModel( … ); … sb->registerListener(vpm); sb->registerListener(vp); vp->setModel(vpm); vpm->setModel(sm); sm->registerListener(sb); … return Fl::run(); } Question: Will this cause serviceNetwork() to be invoked periodically? By whom?

15. K. Stirewalt CSE 335: Software Design At end of “configuration phase” Event Queue Operating system Mouse main sb :...dm :... Application listenermodel...

16. K. Stirewalt CSE 335: Software Design Entering “collaboration phase” Event Queue Operating system FL::run() Mouse main sb :...dm :... Application listenermodel...

17. K. Stirewalt CSE 335: Software Design Step 1.1: App checks event queue Event Queue Operating system FL::run() Mouse main sb :...dm :... Application listenermodel...

18. K. Stirewalt CSE 335: Software Design Step 1.2: App blocks on empty queue Event Queue Operating system FL::run() Mouse main sb :...dm :... Application listenermodel...

19. K. Stirewalt CSE 335: Software Design User then moves scrollbar handle Event Queue Operating system FL::run() Mouse main sb :...dm :... Application listenermodel...

20. K. Stirewalt CSE 335: Software Design Step 1.3: application “wakes” when event arrives Event Queue Operating system FL::run() Mouse leftPress main sb :...dm :... Application listenermodel...

21. K. Stirewalt CSE 335: Software Design Step 1.4: app “pulls” event off queue Event Queue Operating system FL::run() Mouse main sb :...dm :... Application listenermodel...

22. K. Stirewalt CSE 335: Software Design Step 2.1: app “dispatches” event to sb Event Queue Operating system FL::run() Mouse p.pressEvent() main sb :...dm :... Application listenermodel...

23. K. Stirewalt CSE 335: Software Design Step 2.2: sb notifies its listener(s) Event Queue Operating system FL::run() Mouse p.pressEvent() main sb :...dm :... Application listenermodel...

24. K. Stirewalt CSE 335: Software Design Step 2.k: dm is queried for last time Event Queue Operating system FL::run() Mouse p.pressEvent() main sb :...dm :... Application listenermodel...

25. K. Stirewalt CSE 335: Software Design Step 2.k+1: dm query returns Event Queue Operating system FL::run() Mouse p.pressEvent() main sb :...dm :... Application listenermodel...

26. K. Stirewalt CSE 335: Software Design Step 2.k+j: listener.announceNewValue returns Event Queue Operating system FL::run() Mouse p.pressEvent() main sb :...dm :... Application listenermodel...

27. K. Stirewalt CSE 335: Software Design Step 3.1: App checks event queue Event Queue Operating system FL::run() Mouse main sb :...dm :... Application listenermodel...

28. K. Stirewalt CSE 335: Software Design Step 3.2: App blocks on empty queue Event Queue Operating system FL::run() Mouse main sb :...dm :... Application listenermodel...

29. K. Stirewalt CSE 335: Software Design Observations Locus of control : –Resides in object that is activated throughout interaction. –Thus far, our designs have involved single locus of control Stream-manager sequence diagram involves two loci of control: –One for the “the GUI” –One for the stream manager –As yet, we know of no way to build applications with multiple loci of control Question: How could we modify our design to simulate multiple loci of control?

30. K. Stirewalt CSE 335: Software Design Modifications to main() int main (void) { … StreamManager* sm = new StreamManager( … ); … // New event loop while (Fl::check()) { Fl::wait(interval); sm->serviceNetwork(); } return 0; } Note: Replaces call to Fl::run()

31. K. Stirewalt CSE 335: Software Design Strategy Application simulates concurrency by having a “master loop” which periodically cedes control to “concurrent” activities Each activity: –must be designed to be performed via multiple invocations, each of which performs only a small part of the overall task –must never invoke an operation that could block for any perceivable amount of time

32. K. Stirewalt CSE 335: Software Design Question How would we have to modify our program to simulate additional loci of control?

33. K. Stirewalt CSE 335: Software Design Software control and active objects

34. K. Stirewalt CSE 335: Software Design Software control Styles of control in a program 1.Procedural: Control resides in “application code” –Requests for resources block until resource available 2.Event-driven: Control resides in a central dispatcher –Application code does not explicitly requests resources –Rather, application methods are “called back” to handle external events –E.g., mouse clicks, key presses, network traffic, etc. 3.Concurrent: Multiple simultaneous threads of control –New problems to contend with: synchronization –Active vs. passive objects Major design decision that affects the design of lots of individual classes in a system

35. K. Stirewalt CSE 335: Software Design New concept: Active objects StreamManager: example of an active object: –Appears to be running in its own locus of control, distinct from that of the “main application”. –Often needed to monitor asynchronous events : E.g., user input, mouse motion, network traffic Note: Design complexity increases when application involves multiple active objects. –E.g., need to explicitly design dispatcher

36. K. Stirewalt CSE 335: Software Design Exercise Develop a class called GUIManager that simplifies extending the dispatch loop to cede control to active objects –Invent an interface class that all active objects must implement –Active objects register with the Dispatcher (an instance of GUIManager ) to request periodic control

37. K. Stirewalt CSE 335: Software Design ActiveObjectInterface class ActiveObjectInterface { public: virtual int activate() =0; }; The activate operation is invoked to cede a “small quantum” of control to the object that implements this interface Return value (integer) allows active object to return an error code to the dispatcher

38. K. Stirewalt CSE 335: Software Design Class GUIManager class GUIManager { public: GUIManager(); void setTimeoutInterval( float interval ); void registerActiveObject( ActiveObjectInterface* ); int run(); private: float timeoutInterval; vector listeners; };

39. K. Stirewalt CSE 335: Software Design Application of new collaboration class MyStreamManager : public ActiveObjectInterface, public StreamManager { public:... int activate() { return StreamManager::serviceNetwork(); }... }; int main(void) { GUIManagerDispatcher; MyStreamManagersm;... Dispatcher.registerActiveObject(&sm); return Dispatcher.run(); }

40. K. Stirewalt CSE 335: Software Design Questions What happens if the user clicks on scrollbar during the serviceNetwork transaction? What happens to the responsiveness of the user interface if the call to activate() blocks for some perceivable amount of time? How might we fix this?

41. K. Stirewalt CSE 335: Software Design Control implementation strategies Event-driven sequential: Central dispatcher invokes registered objects to service asynchronous events Time-sliced multiplexing: –Scheduler activates each active object in sequence and periodically preempts one actor to schedule another –Generally requires operating-system support –Thread: “Lightweight process”; essentially a unit of time- sliced multiplexing within a sequential process Multi-process: Active objects associated with operating-system processes