Connectors Style: Main program and subroutines

1. ConnectorsStyle: Main program and subroutines INF 123 – Software architecture tdebeauv@uci.edu

2. Outline • Some theory • Connector 1: Procedure call • Style: Main program and subroutines • Connector 2: Socket

3. Some theory

4. Connector • Architectural element in charge of the interactions among components • Connector in implementations • No dedicated code • Scattered across modules • Connector in architectures • Its own spec • To distinguish computations from interactions

5. Connectors • Allow components to transfer control and data with each other • Aka facilitating control flow and data flow What is control?

6. Connectors • “The guards at the gate of separation of concerns” • Often domain-agnostic: the how, not the what I protect that which matters most

7. Connectors • Can be super smart and complex • E.g. order, filter, combine, or discard messages I am a trafficker of information

8. 4 interaction roles • Communication • Transfer of data • Message passing • Coordination • Transfer of control • Function calls • Conversion • Translation • Wrapping • Facilitation • Load-balancing • Locks

9. Connector examples vs concerns • Procedure call • Method call • Event broker • Pubsub • Interrupts • Socket • Load balancer • DB driver • SSH Tunnel • … • Best effort vs exactly once vs reliable • Encrypted vs cleartext • Uni/multi/broadcast • Static vs dynamic linkage • Serialization (JSON, XML, binary) • Stateless vs stateful • Sync vs asynchronous • …

10. Procedure call

11. Procedure call • Communication role • Arguments, return values • Coordination role • Control flow • The most basic connector • “The Assembly language of sw interaction”

12. Examples • Subroutines • Architectural style: Main program and subroutine • Object-oriented methods • UNIX fork and exec • OS calls (open, read, write, poll, …) • Callbacks • Basis for Remote Procedure Call

13. Style: Main program and subroutines

14. Style: Main program and subroutines • Break down a long program into 1 main and N subroutines • Subroutines • Self-contained • No side-effects • Independent of each other • Functionally meaningful and substantial • Good: detect_and_execute_collisions(me, enemies, walls) returns True if the game is over • Bad: add_one_to_score(score) returns score+1

15. Style: Main program and subroutines main Function calls Subroutine 1 Subroutine 2 Subroutine N …

16. Easy to follow the control flow main Subroutine 1 Subroutine 2 Subroutine N …

17. Style: Main program and subroutines while keep_going: keep_going, direction = process_input(direction) mybox = move(mybox, direction) if collide(mybox, borders): mybox, direction = create_box(dims) mybox, pellets = eat_colliding_pellet(mybox, pellets, dims) draw_everything(screen, mybox, pellets, borders) clock.tick(50)

18. Style: Main program and subroutines game loop Function calls process_input move draw_everything … Only these functions involve Pygame

19. Same loop, but replace Pygame display

20. IP Sockets

21. Socket • Endpoint of inter-process communication across the network • Most follow Internet Protocol (IP) • BSD standard IP socket API • Constructor, bind, listen, connect, accept, send, recv, close, setsockopt, … • poll, select, epoll, or kqueue to know the socket state (is there data to recv? The other end hung up?) • Client-server paradigm

22. Client-server paradigm • Server socket bind() and listen() • Server poll() its sockets periodically • Client socket connect() • Client poll() its socket periodically • Server socket accept() • Creates a new socket for that client connection • Both sockets send() and recv() • One socket close() • The other’s poll() will notify the closure

23. Client-server • The client contacts the server • The server can’t pull a client in! • Neo must sit to connect

24. Sequence diagram

25. IP sockets in Python • http://docs.python.org/2/howto/sockets.html • http://docs.python.org/2/library/socket.html