La presentazione tenuta da Simone Bordet in occasione del Codemotion Roma del 5 marzo 2011 - http://www.codemotion.it/ Si parlerà delle web applications di tipo Comet, cioè di quelle web applications che si occupano di notificare con latenza bassissima - di norma a browsers - eventi ricevuti dal server come stock price, eventi sportivi, giochi online, etc. La sessione proseguirà con una discussione sugli impatti che le applicazioni Comet hanno nello sviluppo e nel deployment, e con una panoramica sul nuovo protocollo WebSocket definito da HTML5 e sul progetto open source CometD.

1. Comet and WebSocket Web Applications Simone Bordet [email_address] How to Scale Server-Side Event-Driven Scenarios

3. Impacts of Comet web applications

4. WebSocket web applications

5. The CometD project

6. Questions & Answers

7. What are Comet & WebSocket Web Applications ?

9. Resources download

12. Data download

17. To implement new types of web applications

18. Comet Examples

21. When the number of clients is large

24. A timeout expires

25. The client disconnects

28. Messages can be initiated by the server

33. Impacts on the Server

35. Request Rate: 200 requests/s

39. Request Rate: 50 requests/s, good

43. Note that threads stack memory is outside Java heap

45. You cannot just deploy your Comet web application in a standard configuration

48. The Jetty Continuations allow the Jetty Server to threadlessly suspend requests

49. The continuation concepts have been incorporated in the new Servlet(TM) 3.0 specification

50. Jetty 6 and Jetty 7 successfully deployed Comet applications worldwide

51. Jetty 8 implements the Servlet(TM) 3.0 specification

55. Wait for server-side events is threadless

56. Request is re-run on event arrival or on long poll timeout

57. Request Rate: 100 requests/s, good

58. Only few concurrent active (threaded) requests

60. Scales a lot better than normal polling and blocking Comet

62. Request Rate: 50 requests/s, good

63. Only few concurrent active (threaded) requests

65. Scales a slightly better than Comet with continuations due to better data density and reduced request rate

67. The CometD Project

69. What do we need to write applications ?

72. A clean way to receive data from the server

73. A clean way to “emit” server-side events to clients

74. CometD JavaScript API var cometd = $.cometd; // jQuery style cometd. init ('http://myserver/cometd'); cometd. subscribe ('/my/channel', function(message) { var data = message.data; // Do something with the data }); cometd. publish ('/my/channel', { chatText: 'hello!' }); cometd. disconnect ();

77. Message Acknowledgment

78. Message serialization

82. Java (client and server)

83. Perl & Python (less active)

87. Highly configurable

88. Message batching

89. Automatic reconnection

93. Message batching

94. Lazy messages

95. A variety of listeners to be notified of relevant events in client and server

96. Data filters to automatically convert data

97. Extensions

98. SecurityPolicy

99. Performance

100. DEMO

105. Questions & Answers