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    Kamaelia Europython Tutorial - Presentation Transcript

    1. Kamaelia: Pragmatic Concurrency A Tutorial Michael Sparks Europython '09, Birmingham UK http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    2. About me • - Been using python for several years • - Always been interested in concurrency • - Kamaelia aims to embody safe practices. • - Work at BBC R&D's Northern Lab, based in Manchester, moving to Media City:UK in 2011 • - Kamaelia is born out of a variety of R&D projects, and shaped by needs, not aesthetics or purity. • Kamaelia is not an active R&D project. It is used in R&D projects, and hence actively maintained. http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    3. About me • Disclaimer: Like you, I'm doing this on my time, not the BBC's. This doesn't represent BBC opinion on anything. • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    4. About Kamaelia • - Also born from a desire to make concurrency in programs easier to work with • - Because it's nice in the shell – I want software concurrency that easy :-) • - Expressiveness is favoured over performance, but not to preclude optimisation • - Means we're cautious about adding syntactic sugar. • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    5. About Kamaelia • - Adapts Unix Philosophy to make a program concurrent internally, but with the purpose of simplifying maintenance. • Unix Philosophy: • Write programs that do one thing and do it well. Write programs to work together. Write programs to handle text streams, because that is a universal interface. • --Doug McIlroy • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    6. About Kamaelia • - Adapts Unix Philosophy to make a program concurrent internally, but with the purpose of simplifying maintenance. • Kamaelia Philosophy: • Write components that do one thing and do it well. Write components to work together. Write components to handle python object streams, because that is a universal interface. • --With apologies to Doug McIlroy • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    7. What we're covering • - An overview of Kamaelia • & it's view on concurrency • - How to build a mini Kamaelia • – to get under the hood. • - Building components & systems • - Examining larger systems, and debugging. • - Building a large(ish) system http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    8. Time Estimates • First part: • - An overview of Kamaelia (lightning talkstyle : 5-10 mins) • - How to build a mini Kamaelia (exercise 40-60 mins) • - Starting building components & systems (remainder) After break: • - More advanced stuff (demo/etc 20 mins) • - Larger systems and debugging. (20 mins) • - Building a large(ish) system (exercise 40 mins) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    9. Format • I generally welcome questions at any point • That said... • 'Except in the overview • - the rest of this morning should answer them!! • Copious notes provided - covers more than today • Materials available from URL below • Is a mixture of “explain then do”. Perhaps hold questions for during “do” :-) ? http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    10. Caveat • • * First time I've given this tutorial ! • * If we run short of time on any section, we'll skip ahead. • • * BUT, have copious notes that cover everything. http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    11. Questions? • ... before we dive in? • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    12. Part 1 • • First part: • - An overview of Kamaelia (lightning talk style : 5-10 mins) • - How to build a mini Kamaelia (exercise 40-60 mins) • - Starting building components & systems (remainder) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    13. Kamaelia, a 20:20 overview 20:20 Presentation A presentation style based on the “Pecha Kucha” style 20 slides, 20 seconds each (Similar to a lightning talk) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    14. Why? Hardware finally going massively concurrent ... Opportunity! .... PS3, high end servers, trickling down to desktops, laptops) “many hands make light work” but Viewed as Hard ... do we just have crap tools? “And one language to in Problems the darkness bind them” ... can just we REALLY abandon 50 years of code for Erlang, Haskell and occam? http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    15. Missing Something? Fundamental Control Structures ... in imperative languages number greater than 3! (despite what you get taught...!) Control Structure Traditional Abstraction Biggest Pain Points Sequence Function Global Var Selection Function Global Var Iteration Function Global Var Parallel Thread Shared Data Usually Skipped Lost or duplicate update are most common bugs http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    16. Regarding using concurrency, what sort of applications are we talking about here? Desktop gsoc Media Novice APPS trainee Network 3rd Party http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    17. Think backend Speak 'n Write P2P Whiteboard Programming needed for Simple ER DB Modeller (logo) youtube/flickr Kids Games P2P Radio Torrent type systems 3D Systems Compose Realtime Music UGC Desktop gsoc Paint App Backend P2P Web Server Secure “phone” Transcoder Social Net Vis Media Novice ... Shot Change Detection APPS trainee MiniAxon ScriptReader Mobile DVB MediaPreview Reframing on Mobile Reliable Macro Podcasts Network 3rd Party Multicast Sedna “record everything” XMPP XMLDB Email & AWS pubsub Spam Web (Amazon) SMTP IRC Qt Serving Gtk Greylisting Pop3Proxy ClientSide AIM microblogging Spam Tools http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    18. Core Approach: Concurrent things with comms points Generally send messages Keep data private, don't share outbox inbox outbox inbox signal control signal control ... ... ... ... http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    19. But I must share data? Use Software Transactional Memory ie version control for variables. 1. Check out the collection of values you wish to work on 2. Change them 3. Check them back in 4. If conflict/clash, go back to 1 http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    20. Perspectives in APIs! (1/2) If you have concurrency it becomes natural to think in terms of 1st 2nd and 3rd person. This affects an API's structure, 1st Person - I change my state and can be vital for understanding it! This is one we've found that makes sense 2nd Person – YOU 3rd Person – want to me to do Bla should something do something (you send outbox (I send a message) inbox me a message) control signal ... ... http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    21. Perspectives in APIs! (2/2) If you have concurrency it becomes natural to think in terms of 1st 2nd and 3rd person. This affects an API's structure, private real methods and can be vital for understanding it! This is one we've found that makes sense Messages Messages sent from public to public outboxes inboxes inbox outbox control signal Also, think ... ... Also, think about stdin about stdout http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    22. Actor Systems Distinction can be unclear, potential source of ambiguity* private real methods Messages from public No outbox concept inboxes Possible issues with inbox rate limiting* control Hardcodes recipient ... in the sender *system dependent issue http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    23. Advantages of outboxes No hardcoding of recipient allows: - Late Binding - Dynamic rewiring inbox outbox Concurrency Patterns as control signal Reusable Code ... ... ... a concurrency DSL http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    24. A Core Concurrency DSL Pipeline(A,B,C) Graphline(A=A,B=B, C=C, linkages = {}) Tpipe(cond, C) Seq(A,B,C), PAR(), ALT() Backplane(“name”), PublishTo(“name”), SubscribeTo(“name”) Carousel(...) PureTransformer(...) StatefulTransformer(...) PureServer(...) MessageDemuxer(...) Source(*messages) NullSink Some of these are work in progress – they've been identified as useful, but not implemented as chassis, yet http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    25. Pipeline Example Pipeline( MyGamesEventsComponent(up="p", down="l", left="a", right="s"), BasicSprite("cat.png", name = "cat", border=40), ).activate() MyGames Events Component Basic Sprite http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    26. Graphline Example Graphline( NEXT = Button(...), PREVIOUS = Button(...), PREVIOUS NEXT FIRST = Button(...), (button) (button) LAST = Button(...), CHOOSER = Chooser(...), IMAGE = Image(...), FIRST LAST (button) (button) ... ).run() Chooser Image http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    27. Server Example data from user data Main Socket handler Server Core to user Created at runtime to handle the Protocol Handler Factory connection Remote Protocol handler User http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    28. Server Example You therefore need to provide Main this bit. Server Core Protocol Handler Factory http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    29. Server Example from Kamaelia.Chassis.ConnectedServer import ServerCore from Kamaelia.Util.PureTransformer import PureTransformer def greeter(*argv, **argd): return PureTransformer(lambda x: "hello" +x) class GreeterServer(ServerCore): protocol=greeter port=1601 GreeterServer().run() http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    30. Backplane Example # Streaming Server for raw DVB of Radio 1 Backplane(“Radio”).activate() Pipeline( DVB_Multiplex(850.16, [6210], feparams), # RADIO ONE PublishTo("RADIO"), ).activate() def radio(*argv,**argd): return SubscribeTo(“RADIO”) ServerCore(protocol=radio, port=1600).run() http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    31. So that's the 5 minute version Short Q&A before we move on? http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    32. Part 1 • • First part: • - An overview of Kamaelia (lightning talk style : 5-10 mins) • - How to build a mini Kamaelia (exercise 40-60 mins) • - Starting building components & systems (remainder) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    33. Mini Axon • Kamaelia is divided into two halves • * One part handles all the concurrency stuff, providing you a component model • * The other is a large collection of components and some apps using them. http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    34. Mini Axon • Axon is the part that handles concurrency and provides the component model, and is the key to understanding why & how Kamaelia works. http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    35. Mini Axon • ... is a collection of exercises where you build just such a beast. http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    36. Mini Axon • • Generators * Python's smallest unit of concurrency • Microprocesses * Generators with context • Scheduler * Something to run lots of microprocesses • Components * A microprocess with boxes (treated as in & outboxes) • Postman * Something to do deliveries http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    37. Mini Axon • • Generators * Python's smallest unit of concurrency • Microprocesses * Generators with context • Scheduler * Something to run lots of microprocesses • Components * A microprocess with boxes (treated as in & outboxes) • Postman * Something to do deliveries http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    38. Generators • * Python's smallest unit of concurrency • * Single function you call, get a generator back • * Can then call it's .next() method to * Get a new value from it * Give it CPU time http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    39. Fibonacci Generator • def fib(a,b): while 1: yield a a, b = b, b + a • • Demo http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    40. Fibonacci Generator • >>> def fib(a,b): ... while 1: ... yield a ... a, b = b, b + a ... >>> g = fib(1,1) >>> g <generator object at 0xb7bf9c6c> >>> [ g.next() for _ in range(10) ] [1, 1, 2, 3, 5, 8, 13, 21, 34, 55] • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    41. Lots of Generators • Using the same fib generator, make 10 of them: >>> GS = [ fib(x,x) for x in range(10) ] • And “run” them: >>> [ G.next() for G in GS ] [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] >>> [ G.next() for G in GS ] [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] >>> [ G.next() for G in GS ] [0, 2, 4, 6, 8, 10, 12, 14, 16, 18] >>> [ G.next() for G in GS ] [0, 3, 6, 9, 12, 15, 18, 21, 24, 27] >>> [ G.next() for G in GS ] [0, 5, 10, 15, 20, 25, 30, 35, 40, 45] • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    42. Generators as co-routines • def fib(a,b): while 1: yield 1 # Just to say “keep running me” print a a, b = b, b + a • • Demo http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    43. Generators as co-routines • def printer(tag): while 1: yield 1 # Makes it a generator print tag • • Demo http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    44. Mini Axon • • Generators * Python's smallest unit of concurrency • Microprocesses * Generators with context • Scheduler * Something to run lots of microprocesses • Components * A microprocess with boxes (treated as in & outboxes) • Postman * Something to do deliveries http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    45. Microprocesses • * Generators with context • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    46. microprocess exercise • Write a class microprocess with methods: • __init__(self) * Takes no arguments * Uses super to call superclass __init__ method • main(self) * No arguments * Should yield 1 • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    47. microprocess answer • • class microprocess(object): def __init__(self): super(microprocess, self).__init__() def main(self): yield 1 • Generally, we'll skip answers in this presentation, they're all in the web version of this tutorial here: • http://www.kamaelia.org/MiniAxon/ • (and in the notes :-) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    48. microprocess usage • class printer(microprocess): def __init__(self, tag): super(printer, self).__init__() self.tag = tag def main(self): while 1: yield 1 print self.tag • • “Printer” isn't particularly interesting, but allows things like components, but let's see how this can be used. http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    49. microprocess usage 2 • >>> X = printer("Something") >>> G = X.main() >>> X,G (<__main__.printer object at 0xb7bfd2ac>, <generator object at 0xb7bfd4cc>) >>> G.next() 1 >>> G.next() Something 1 >>> X.tag = "Something else" >>> G.next() Something else 1 http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    50. Mini Axon • • Generators * Python's smallest unit of concurrency • Microprocesses * Generators with context • Scheduler * Something to run lots of microprocesses • Components * A microprocess with boxes (treated as in & outboxes) • Postman * Something to do deliveries http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    51. Scheduler • * Something to run lots of microprocesses • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    52. scheduler exercise • Write a class scheduler with 3 methods: • __init__(self) * Uses super to call superclass __init__ method * subclasses microprocess * Creates 2 queues – active & newqueue • main(self) * Is a generator * Runs the microprocesses activated • activateMicroprocess(self, someprocess): * Calls somprocess.main() * Adds generator to newqueue • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    53. scheduler exercise • Scheduler logic • main(self) * loops 100 times, yields 1 at start of loop * loop through generators in self.active * call their .next() method * If result is not -1 and no StopIteration, append to newqueue * at end of loop, newqueue becomes active * newqueue reset to empty list • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    54. scheduler usage • Using same printer class.. • >>> X = printer("Hello World") >>> Y = printer("Game Over") # :-) • >>> myscheduler = scheduler() >>> myscheduler.activateMicroprocess(X) >>> myscheduler.activateMicroprocess(Y) • >>> for _ in myscheduler.main(): ... pass • <prints Hello world/Game over repeatedly> http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    55. Mini Axon • • Generators * Python's smallest unit of concurrency • Microprocesses * Generators with context • Scheduler * Something to run lots of microprocesses • Components * A microprocess with boxes (treated as in & outboxes) • Postman * Something to do deliveries http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    56. Component • • * microprocess with a standard interface. • boxes as inboxes/outboxes • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    57. component exercise • Write a class component subclass of microprocess with 4 methods: • __init__(self) send(self, value, outboxname) recv(self, inboxname) dataReady(self, inboxname) • Behaviour coming up! http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    58. component exercise 1/4 • __init__(self) logic: * Add an attribute self.boxes, default value: { “inbox”: [], “outbox”: [] } • * Ensure you call the superclass __init__ method appropriately • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    59. component exercise 2/4 • send(self,value, outboxname) logic: Finds the list named outboxname in self.boxes, and appends value to it. • Before: X.send(“hello”, “outbox”) { “inbox”: [], “outbox”: [] } • After: { “inbox”: [], “outbox”: [“hello”] } • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    60. component exercise 3/4 • recv(self, inboxname) logic: Finds the list named inboxname in self.boxes, and pops the first value • Given: { “inbox”: [“hello”, “world”], “outbox”: [] } • self.recv(“inbox”) returns, “hello” leaving... { “inbox”: [“world”], “outbox”: [] } • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    61. component exercise 4/4 • dataReady(self, inboxname) logic: Finds the list named inboxname in self.boxes: returns the length of the list. • Given: { “inbox”: [“hello”, “world”], “outbox”: [] } • dataReady(“inbox”) --> 2 (allows if self.dataReady(“inbox”) ) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    62. component usage • Until we add a means for data to get from outboxes to inboxes, using components is no more interesting than microprocesses http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    63. Mini Axon • • Generators * Python's smallest unit of concurrency • Microprocesses * Generators with context • Scheduler * Something to run lots of microprocesses • Components * A microprocess with boxes (treated as in & outboxes) • Postman * Something to do deliveries http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    64. Postman • * Something to do deliveries • • Note: This is more conceptual in real Axon, but was real in v. old Axon. ie real Axon is more efficient! http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    65. postman exercise • Write a class postman subclass of microprocess with 2 methods: • __init__(self, source, sourcebox, sink, sinkbox) main(self) • Behaviour coming up! http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    66. postman exercise 1/4 • __init__(self, source, sourcebox, sink, sinkbox) logic: * Copy all the arguments as local attributes • * Ensure you call the superclass __init__ method appropriately! • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    67. postman exercise 2/4 • main(self) logic: • In a loop: • yield a non -1 value (eg 1) Check if source's sourcebox has dataReady • If it has, use recv to collect it from there, and sink's send method to deliver it. http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    68. Mini Axon • • Using it! http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    69. Producer/Consumer 1/3 • • class Producer(component): def __init__(self, message): super(Producer, self).__init__() self.message = message • def main(self): while 1: yield 1 self.send(self.message, "outbox") • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    70. Producer/Consumer 2/3 • • class Consumer(component): def main(self): count = 0 while 1: yield 1 count += 1 if self.dataReady("inbox"): data = self.recv("inbox") print data, count • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    71. Producer/Consumer 3/3 • • p = Producer("Hello World") c = Consumer() postie = postman(p, "outbox", c, "inbox") • myscheduler = scheduler() myscheduler.activateMicroprocess(p) myscheduler.activateMicroprocess(c) myscheduler.activateMicroprocess(postie) • for _ in myscheduler.main(): pass • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    72. Producer/Consumer Output • • Hello World 2 Hello World 3 Hello World 4 • ... • Hello World 96 Hello World 97 Hello World 98 • • Not 100, because of yields before start of scheduler loop. (scheduler terminates early) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    73. Mini Axon • • Using it for more useful stuff http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    74. File Reader • • class FileReader(component): • def __init__(self, filename): super(FileReader, self).__init__() self.file = open(filename, "rb",0) • def main(self): yield 1 for line in self.file.xreadlines(): self.send(line, "outbox") yield 1 http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    75. Multicast sender 1/2 • class Multicast_sender(component): def __init__(self, laddr, lport, daddr, dport): super(Multicast_sender, self).__init__() self.laddr = laddr self.lport = lport self.daddr = daddr self.dport = dport • ... continued http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    76. Multicast sender 2/2 • class Multicast_sender(component): ... continued def main(self): sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP) sock.bind((self.laddr,self.lport)) sock.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, 10) while 1: if self.dataReady("inbox"): data = self.recv("inbox") l = sock.sendto(data, (self.daddr,self.dport) ) yield 1 • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    77. FileReader -> MulticastSender • • reader = FileReader("Ulysses") sender = Multicast_sender("0.0.0.0", 0, "224.168.2.9", 1600) postie = Postman(reader, "outbox", sender, "inbox") • • myscheduler = scheduler() myscheduler.activateMicroprocess(reader) myscheduler.activateMicroprocess(sender) myscheduler.activateMicroprocess(postie) • for _ in myscheduler.main(): pass • • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    78. Mini Axon --> Axon • • The rest is: Syntactic Sugar Ways of using it Optimisations (eg direct delivery – no postman) + a couple of other ideas we'll come to (STM, threadedcomponents, services, processcomponents) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    79. Questions? • • ... before we look how to build some real components, and how to use them? • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    80. Part 1 • • First part: • - An overview of Kamaelia (lightning talk style : 5-10 mins) • - How to build a mini Kamaelia (exercise 40-60 mins) • - Starting building components & systems (remainder) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    81. Building a Video Recorder • • Before the break, we'll build a simple video recorder. • Approach: • 1 Build a webcam • 2 Clean up the code for “normal” reuse • 3 Componentise in least effort manner • 4 Separate input/transform/display parts • 5 Hook webcam up to a dirac encoder and filewriter • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    82. Step 1: Build a simple Webcam • Pygame 1.9.1 alpha has basic Linux webcam support which works nicely, so we're using that. • First some initialisation • import pygame import pygame.camera • pygame.init() pygame.camera.init() http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    83. Step 1: Build a simple Webcam • The some definitions: • displaysize = (800, 600) capturesize = (640, 480) imagesize = (352, 288) imageorigin = (0,0) device = “/dev/video0” http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    84. Step 1: Build a simple Webcam • Initialise the display, allocate a camera, and activate it • display = pygame.display.set_mode(displaysize) camera = pygame.camera.Camera(device, capturesize) camera.start() http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    85. Step 1: Build a simple Webcam • Loop round capturing images and display them • while 1: snapshot = camera.get_image() snapshot = pygame.transform.scale(snapshot, imagesize) display.blit(snapshot, imageorigin) pygame.display.flip() • • Demo! http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    86. Step 2: Clean up for reuse • Given a collection of config options, wrapping this in a class makes sense. • As before these parts are unchanged: • import pygame import pygame.camera • pygame.init() pygame.camera.init() • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    87. Step 2: Clean up for reuse • We then define a class, and put the config options as class attributes: • class VideoCapturePlayer(object): • displaysize = (800, 600) capturesize = (640, 480) imagesize = (352, 288) imageorigin = (0,0) device = “/dev/video0” http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    88. Step 2: Clean up for reuse • Put our initialisation in the __init__. Allow the user to override our defaults def __init__(self, **argd): self.__dict__.update(**argd) super(VideoCapturePlayer,self).__init__() self.display = pygame.display.set_mode(self.displaysize) self.camera = pygame.camera.Camera(self.device, self.capturesize) self.camera.start() http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    89. Step 2: Clean up for reuse • Wrap up body of loop in a method def get_and_flip(self): snapshot = self.camera.get_image() snapshot = pygame.transform.scale(snapshot, self.imagesize) self.display.blit(snapshot, self.imageorigin) pygame.display.flip() http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    90. Step 2: Clean up for reuse • Provide a hook to start it going, wrapping the main loop. def main(self): while 1: self.get_and_flip() • Then run it! VideoCapturePlayer().main() • • Demo! http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    91. Step 3: Componentise • • In this case, least effort approach is to use a threaded component. Would could make it a generator component later if needed. • Changes: • * imports * class's baseclass / extraction of display_flip into a method. (to simplify later integration with existing components) * how we run it. http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    92. Step 3: Componentise • • Imports change to import pygame import pygame.camera from Axon.ThreadedComponent import threadedcomponent • pygame.init() pygame.camera.init() • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    93. Step 3: Componentise • • Baseclass changes & initialiser changes: class VideoCapturePlayer(threadedcomponent ): ... def __init__(self, **argd): # no longer update __dict__ here super(VideoCapturePlayer,self).__init__(**argd ) ... http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    94. Step 3: Componentise • • Extract display flipping out to a separate method: def pygame_display_flip(self): pygame.display.flip() def get_and_flip(self): snapshot = self.camera.get_image() snapshot = pygame.transform.scale(snapshot, self.imagesize) self.display.blit(snapshot, self.imageorigin) self.pygame_display_flip() http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    95. Step 3: Componentise • • Change to how we run: • We had: • VideoCapturePlayer().main() • We now: • VideoCapturePlayer().run() • • Demo! http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    96. Step 4: Split into input & output • • Now we can split the component in two: • * VideoCaptureSource • * Surface Displayer • The Video capture source now needs to be self regulating, so it needs to sleep during the loop, relative to a target frame rate. http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    97. Step 4: Split into input & output • • VideoCaptureSource class preamble: • import time class VideoCaptureSource(threadedcomponent): capturesize = (352, 288) delay = 0 fps = -1 device = “/dev/video0” • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    98. Step 4: Split into input & output • • VideoCaptureSource initialiser • def __init__(self, **argd): super(VideoCaptureSource, self).__init__(**argd) self.camera = pygame.camera.Camera(self.device, self.capturesize) self.camera.start() if self.fps != -1: self.delay = 1.0/self.fps self.snapshot = None http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    99. Step 4: Split into input & output • • Main loop body now just captures images, capturing a reference • def capture_one(self): • self.snapshot = None self.snapshot = self.camera.get_image() http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    100. Step 4: Split into input & output • • Main loop still runs it, and sends the image out an outbox, and then sleeps. • def main(self): • while 1: self.capture_one() self.send(self.snapshot, “outbox”) time.sleep(self.delay) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    101. Step 4: Split into input & output • • The surface displayer takes the other code chunks • from Axon.Component import component • class SurfaceDisplayer(component): displaysize = (800,600) imagesize = (352, 288) imageorigin = (0,0) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    102. Step 4: Split into input & output • • Has it's own initialiser... • def __init__(self, **argd): super(SurfaceDisplayer, self).__init__(**argd) self.display = pygame.display.set_mode(self.displaysize) • Retains the following method unchanged: • def pygame_display_flip(self): pygame.display.slip() http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    103. Step 4: Split into input & output • Then mainbody waits for surfaces to display, sleeping when there isn't any: • def main(self): • while 1: while self.dataReady(“inbox”): snapshot = self.recv(“inbox”) snapshot = pygame.transform.scale(snapshot, self.imagesize) self.display.blit(snapshot, self.imageorigin) • while not self.anyReady(): self.pause() yield 1 • yield 1 http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    104. Step 4: Split into input & output • • We then join these back together in a pipeline: • from Kamaelia.Chassis.Pipeline import Pipeline • Pipeline( • VideoCaptureSource(), • SurfaceDisplayer(), • ).run() • Demo! http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    105. Step 5: Recording • Working back... • • We want to write to a file... (SimpleWriter) • We want to write dirac encoded video DiracEncoder • That expects YUV Frames (ToYUV420_planar) • That expects RGB data + metadata PureTransformation of somr RGB data • Which needs a picture source • Which is where we started. http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    106. Step 5: Recording • Our imports therefore need to add: • • from Kamaelia.File.Writing import SimpleFileWriter • from Kamaelia.Codec.Dirac import DiracEncoder • from Kamaelia.Video.PixFormatConversion import ToYUV420_planar • from Kamaelia.Util.PureTransformer import PureTransformer • • And we delete everything related to display http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    107. Step 5: Recording • We then need to join it all together: • Pipeline( • VideoCaptureSource(), PureTransformer(lambda F : {"rgb" : pygame.image.tostring(F, "RGB"), "size" : (352, 288), "pixformat" : "RGB_interleaved", }), ToYUV420_planar(), DiracEncoder(preset="CIF", encParams={"num_L1":0}), SimpleFileWriter("X.drc"), • ).run() http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    108. Step 5: Recording • • This then records dirac encoded video, which we can now playback with a simple dirac player! • • Demo ! • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    109. Questions? • ... before we break? • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    110. End of Part 1 • • Before the second half, download and install Kamaelia from the link below, if you haven't already. • • http://tinyurl.com/kot49x • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    111. Kamaelia: Pragmatic Concurrency A Tutorial Michael Sparks Europython '09, Birmingham UK http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    112. Part 2 • • Second part: • - More advanced stuff (demo/etc 20 mins) • - Larger systems, embedding and debugging. (20 mins) • - Building a large(ish) system (exercise 40 mins) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    113. Questions? • ... before we carry on? • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    114. Part 2 • • Second part: • - More advanced stuff (demo/etc 20 mins) • - Larger systems and debugging. (20 mins) • - Building a large(ish) system (exercise 40 mins) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    115. More advanced Stuff • Have seen how to build a basic component and a basic system - covers a wide set of problems. Now we broaden the scope. • • If we have time we'll come back to Kamaelia's STM model & concepts of services, and (experimental) multiple process support. http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    116. Well behaved Shutdown • Components should expect to receive these messages on their “control” inbox, and behave as follows: • Axon.Ipc.shutdownMicroprocess – if you receive this, you are expected to shutdown immediately, and to pass this message on. • Axon.Ipc.producerFinished – if you receive this, someone sending you data has shutdown. You may want to shutdown depending on your application's logic. You may process all outstanding messages in this case. You may wish to pass this message on, or change it to shutdownMicroprocess if it was unexpected. • Due to different component needs no syntactic sugar exists for this, but common cases are being discussed at present. http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    117. Components • Inheritable default values – we've already seen this! • class VideoCapturePlayer(threadedcomponent): displaysize = (800, 600) capturesize = (640, 480) imagesize = (352, 288) imageorigin = (0,0) device = "/dev/video0" • Also usable: • VideoCapturePlayer(device = "/dev/video0") VideoCapturePlayer(device = "/dev/video1") http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    118. Components • Inheritable default values – other places: class ServerCore(component): port=1601 protocol=None socketOptions=None TCPS=TCPServer .... http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    119. Components • Inheritable default values: class MailServer(ServerCore): port=25 protocol=SMTPProtocol • Usage: • MailServer().run() MailServer(port=8025).run() MailServer(socketOptions=...).run() • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    120. Components • Inheritable default values - nests class MyReconfiguredMailServer(MailServer): port=25 protocol=SMTPProtocol socketOptions = socketOptions=(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) class TCPS(TCPServer): CSA=MyDebugWrapper(ConnectedSocketAdapter) • Allows for deep reconfiguration of components, without rewriting. http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    121. Components • Inheritable default values – real usage – Kamaelia Grey class GreylistServer(MoreComplexServer): logfile = config["greylist_log"] debuglogfile = config["greylist_debuglog"] socketOptions=(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) port = config["port"] class TCPS(TCPServer): CSA = NoActivityTimeout(ConnectedSocketAdapter, timeout=config["inactivity_timeout"], debug=False) class protocol(GreyListingPolicy): servername = config["servername"] serverid = config["serverid"] smtp_ip = config["smtp_ip"] smtp_port = config["smtp_port"] allowed_senders = config["allowed_senders"] allowed_sender_nets = config["allowed_sender_nets"] ... http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    122. Pipelines • Seen how Pipelines can join components together. • However also can do: • Pipeline( Lsystem(), ConsoleEchoer(tag="n", forwarder=True), Damage(), circular = True, ).run() • To enable a feedback loop. (Demo) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    123. Pipelines • Transcode Engine • Pipeline( DirectoryWatcher(watch = conf["main_incoming_queue"]), ImageMover(destdir = conf["image_queue"]), ).activate() • Pipeline( DirectoryWatcher(watch = conf["image_queue"]), ImageTranscoder(destdir = conf["image_moderation_queue"]), ).activate() • Pipeline( DirectoryWatcher(watch = conf["main_incoming_queue"]), VideoMover(destdir = conf["video_queue"]), ).activate() • Pipeline( DirectoryWatcher(watch = conf["video_queue"]), VideoTranscoder(destdir = conf["video_moderation_queue"]), ).run() http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    124. Pipelines • Reusable Dirac Video Source: • def DiracWebCam(): return Pipeline( VideoCaptureSource(), PureTransformer(lambda F : {"rgb" : pygame.image.tostring(F, "RGB"), "size" : (352, 288), "pixformat" : "RGB_interleaved", }), ToYUV420_planar(), DiracEncoder(preset="CIF", encParams={"num_L1":0}), ) • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    125. Graphlines • Graphlines are like pipelines, but any shape. For example, a simple presentation tool: • Graphline( CHOOSER = Chooser(items = files), IMAGE = Image(size=(800,600), position=(8,48)), NEXT = Button(caption="Next", msg="NEXT", position=(72,8)), PREVIOUS = Button(caption="Previous", msg="PREV", position=(8,8)), FIRST = Button(caption="First", msg="FIRST",position=(256,8)), LAST = Button(caption="Last", msg="LAST",position=(320,8)), linkages = { ("NEXT","outbox") : ("CHOOSER","inbox"), ("PREVIOUS","outbox") : ("CHOOSER","inbox"), ("FIRST","outbox") : ("CHOOSER","inbox"), ("LAST","outbox") : ("CHOOSER","inbox"), ("CHOOSER","outbox") : ("IMAGE","inbox"), } ).run() http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    126. Graphlines • • * Swiss Army Knife of Kamaelia components • * Allows almost any topology • - BUT an outbox may only link to one inbox • - many outbox may link to one inbox • * Can contain any component – including pipelines and graphlines • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    127. Graphlines • SMS Outbound processor • Graphline( SMS_SOURCE = Pipeline( DirectoryWatcher(watch = "outgoingsms"), FilesToProcessSource(), FileSlurper(tuplemode=True), ), CLEANER = Pipeline( PureTransformer(lambda (x,y): y ), Mover(), ), SENDER = Pipeline( PureTransformer(lambda (x,y): cjson.decode(x) ), SMSSender(), ), SPLIT = TwoWaySplitter(), http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    128. Graphlines • SMS Outbound processor (cont) • Linkages = { ("SMS_SOURCE","outbox") : ("SPLIT","inbox"), ("SPLIT", "outbox") : ("CLEANER", "inbox"), ("SPLIT", "outbox2") : ("SENDER", "inbox"), } ).run() • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    129. Graphlines • Linkages to or from “self” (or “”) link to the Graphline's boxes. • Graphline( SPLIT = SomeSplitter() MERGE = SomeMerger() P1 = SomeTransformer() P2 = SomeTransformer() P3 = SomeTransformer() linkages { (“self”, “inbox”) : (“SPLIT”, “inbox”), (“MERGE”, “outbox”) : (“self”, “outbox”), ... } • Allows graphlines to nest, and higher level abstractions http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    130. Graphlines • Whiteboard using nesting graphlines: • Pipeline( chunks_to_lines(), lines_to_tokenlists(), Graphline( ROUTER = Router( ((lambda T : T[0]=="SOUND"), "audio"), ((lambda T : T[0]!="SOUND"), "whiteboard"), ), WHITEBOARD = FilteringPubsubBackplane(whiteboardBackplane), AUDIO = Pipeline( SimpleDetupler(1), # remove 'SOUND' tag SpeexDecode(3), FilteringPubsubBackplane(audioBackplane, dontRemoveTag=True), RawAudioMixer(), SpeexEncode(3), Entuple(prefix=["SOUND"],postfix=[]), ), http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com •
    131. Graphlines • Whiteboard using nesting graphlines: • Linkages = { # incoming messages go to a router ("", "inbox") : ("ROUTER", "inbox"), • # distribute messages to appropriate destinations ("ROUTER", "audio") : ("AUDIO", "inbox"), ("ROUTER", "whiteboard") : ("WHITEBOARD", "inbox"), • # aggregate all output ("AUDIO", "outbox") : ("", "outbox"), ("WHITEBOARD", "outbox") : ("", "outbox"), • # shutdown routing ("", "control") : ("ROUTER", "control"), ("ROUTER", "signal") : ("AUDIO", "control"), ("AUDIO", "signal") : ("WHITEBOARD", "control"), ("WHITEBOARD", "signal") : ("", "signal") }, ), tokenlists_to_lines(), ) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    132. Backplanes • • * For where you want 1 to many or many to many • * Declare a backplane • * Components can publish data to it • * Components may subscribe to it. • * Subscribers get a copy of all data sent • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    133. Backplanes • Can be useful for updating a central state. • • For example players locations can be posted here: • Backplane("PLAYERS").activate() • • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    134. Backplanes • Players Post their updates like this: • Pipeline( • MyGamesEventsComponent(up="p", down="l", left="a", right="s"), • BasicSprite("cat.png", name = "cat", border=40), • PureTransformer(lambda x: ("Cat ", x)), • PublishTo("PLAYERS"), • ).activate() • • • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    135. Backplanes • The system can analyse their updates like this: • Pipeline( • SubscribeTo("PLAYERS"), • PlayerAnalyser(), • Distancer(), • ConsoleEchoer(), • ).activate() • • • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    136. Backplanes & Servers • When combined with a server, you instantly get a pub/ sub capable server, or splitter, or merger. • Backplane(“SPLIT”).activate() Pipeline( DiracWebCam(), PublishTo(“SPLIT”), ).activate() def VideoProtocol(**argd): return SubscribeTo(“SPLIT”) • ServerCore(protocol=VideoProtocol, port=1700).run() http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    137. Backplanes & Servers • When combined with a server, you instantly get a pub/ sub capable server, or splitter, or merger. • Backplane(“CHAT”).activate() def ChatProtocol(**argd): return Pipelines( SubscribeTo(“CHAT”) NullComponent(), PublishTo(“CHAT”) ) • ServerCore(protocol=ChatProtocol, port=1700).run() http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    138. PAR & Seq • PAR & Seq are wrapper components with concepts nabbed from Occam. (hence their names) • * Seq runs each component it's given, one after another, wiring up inboxes/outboxes such that each component handles it. Useful in staged protocols (later) • * PAR runs all the components concurrently. Their output is merged. Shutdown messages sent to PAR are forwarded to all subcomponents – making it useful for managing system shutdown. • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    139. Using PAR • PAR can be used to simplify some systems: • Pipeline( PAR( Button(caption="Next", msg="NEXT", position=(72,8)), Button(caption="Previous", msg="PREV", position=(8,8)), Button(caption="First", msg="FIRST" ,position=(256,8)), Button(caption="Last", msg="LAST", position=(320,8)), ), • Chooser(items = files), Image(size=(800,600), position=(8,48)), ).run() • This is the same slideshow as the previous Graphline... http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    140. Using PAR • ... to run & shutdown multiple subsystems • Pipeline( timedShutdown(TTL=15), PAR( Pipeline( ReadFileAdaptor(file, readmode="bitrate", bitrate = 300000*8/5), DiracDecoder(), MessageRateLimit(framerate), VideoOverlay(position=(260,48), size=(200,300)), ), Pipeline( ReadFileAdaptor(file, readmode="bitrate", bitrate = 2280960*8), DiracDecoder(), ToRGB_interleaved(), VideoSurface(size=(200, 300), position=(600,48)), ), http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    141. Using PAR • ... to run & shutdown multiple subsystems • Pipeline( PAR(Button(caption="Next", msg="NEXT", position=(72,8)), Button(caption="Previous", msg="PREV", position=(8,8)), Button(caption="First", msg="FIRST" ,position=(256,8)), Button(caption="Last", msg="LAST", position=(320,8)), ), Chooser(items = files), Image(size=(200,300), position=(8,48), maxpect=(200,300)), ), Pipeline( Textbox(size=(200,300), position=(8,360)), TextDisplayer(size=(200,300), position=(228,360)), ), Ticker(size=(200,300), position=(450,360)), ), ).run() http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    142. Using Seq • An example from the mobile reframer: • Seq( "Decoding & separating frames...", Graphline( MAXF = DetermineMaxFrameNumber(edlfile), DO = Carousel( ... ), STOP = TriggeredOneShot(""), ... ), "Processing edits...", Graphline( REFRAMING = ReframeVideo(edlfile... SOUND = PassThroughAudio(edlfile... ENCODING = ReEncode(outFileName... ... ), "Cleaning up...", StopSelector(), ).run() http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    143. Using Seq • An example of passing state in a protocol handler: • def CompositeBulletinBoardProtocol(**argd): ConnectionInfo = {} ConnectionInfo.update(argd) return Seq( Authenticator(State = ConnectionInfo), UserRetriever(State = ConnectionInfo), MessageBoardUI(State = ConnectionInfo), StateSaverLogout(State = ConnectionInfo), ) ServerCore(protocol=CompositeBulletinBoardProtocol, ...) • Worth noting the similarity between this and wsgi. (Except Seq can contain graphlines, pipelines, etc too) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    144. Part 2 • • Second part: • - More advanced stuff (demo/etc 20 mins) • - Larger systems and debugging. (20 mins) • - Building a large(ish) system (exercise 40 mins) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    145. Larger Systems & Debugging • Large systems which are long running can develop bugs which are awkward to debug. • Kamaelia has a collection of tools you can use which we'll walk through / demonstrate next. • • Practical example. http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    146. Larger Systems & Debugging • Key Tools: • * Instrumentation using backplanes & logging • * Axon Visualiser • * Embeddable python console • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    147. Larger Systems & Debugging • • Practical examples. http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    148. Part 2 • • Second part: • - More advanced stuff (demo/etc 20 mins) • - Larger systems and debugging. (20 mins) • - Building a large(ish) system (exercise 40 mins) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    149. Building a Bulletin Board • We're going to build an “old school” bulletin board system. • * Someone telnets in & authenticates • * Can get help, exit or read messages • * Reading messages, they can read, reply, exit reading, or get help • * State is restored/saved at session start/end http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    150. Building a Bulletin Board • For practicality, we won't implement message posting, nor message deletion, nor persistent user state. (Though these would be useful exercises) • All on-disk objects encoded as json objects: * users * Messages – stored in “folders” (directories) with filenames == messageid • * message fields: from, to, __body__, date, message, reply-to, subject http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    151. Building a Bulletin Board • Getting started: • * Start with basic server for request/response Just echo initially - BB1.py • * make restarting quicker for debugging - BB2.py * abstract out “getting a line of data” - BB3.py * Then use that abstraction - BB4.py * Simplify “control” box handling - BB5.py * Abstract out reusable bits from domain specific – BB6.py • We'll go through the code for these in the actual code files rather than on these slides • (rather unwieldy as slides) http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    152. Building a Bulletin Board • Intermediate Plan • This is the logic of the user protocol • Seq( • Authenticator( <some shared state> ), • UserRetriever( <some shared state> ), • MessageBoardUI( <some shared state> ), • StateSaverLogout( <some shared state> ), • ) • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    153. Building a Bulletin Board • Intermediate Plan • * Tidy up control handling a touch more & add netPrint method to reusable bit - BB7.py • * Change Authenticator component to support the “passed on state”, change protocol handler factory to create that Seq pipeline. - BB8.py • * Change Authenticator to authenticate against a password file and set “remoteuser” in the shared state - BB9.py • * Write stubs for UserRetriever & StateSaverLogout - BB10.py • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    154. Building a Bulletin Board • Final UI Plan • * Change usage of waitMsg to yield self.waitMsg() -- BB11.py • * Copy Authenticator's patten to create initial menu for MessageBoardUI, including stub for messages menu - BB12.py • * Use same pattern for messages menu, use waitMsg pattern for logic. - BB13.py • * Implement Folders to hold messages. Numbers as filenames (msg 1, 2, 3, 4) Messages as json encoded objects - BB14.py • * Clean up to add a line oriented buffer to handle partial lines. (necessary for cross platform/real world) - BB15.py http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    155. Building a Bulletin Board • Final UI Plan • * Change usage of waitMsg to yield self.waitMsg() -- BB11.py • * Copy Authenticator's patten to create initial menu for MessageBoardUI, including stub for messages menu - BB12.py • * Use same pattern for messages menu, use waitMsg pattern for logic. - BB13.py • * Implement Folders to hold messages. Numbers as filenames (msg 1, 2, 3, 4) Messages as json encoded objects - BB14.py • * Clean up to add a line oriented buffer to handle partial lines. (necessary for cross platform/real world) - BB15.py http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    156. Summary • We've covered • * the 30,000 view of kamaelia • * Building your own core • * Building components, including a video recording application • * Tools for building systems • * Tools for debugging systems • * Built a large(ish) system (an authenticated staged protocol) • * Illustrated the majority of this using real world systems http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    157. Final Questions? • • http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com
    158. Thank you! ¬ http://www.kamaelia.org/PragmaticConcurrency sparks.m@gmail.com

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