This document discusses using Scala for concurrent programming in WebObjects applications. It begins by explaining why concurrent programming is important due to increasing numbers of processor cores. It then discusses challenges with traditional threading and locks and introduces the actor model as an easier and more scalable approach using message passing. The document demonstrates how to build concurrent WebObjects applications using Scala actors for processing tasks like video encoding. It shows how properties can configure WebObjects for concurrent requests and how ERXEC provides thread safety. Benchmarks show the Scala actor approach outperforms traditional threading. The document argues that Scala is a powerful, safe and easy language for concurrent programming in WebObjects.

1. WebObjects + Scala
Building Concurrent WebObjects applications with Scala
Ravi Mendis

2. Why Concurrent Programming?

3. 2005
The year of Dual Core

6. 2010
Today

7. Entry-Level
Cores Threads
AMD Opteron 4 4
IBM Power7 4 16
Intel Xeon 4 8

8. High-End
Cores Threads
AMD Opteron 12 12
IBM Power7 8 32
Intel Xeon 6 12

9. 2011
Tomorrow

10. Roadmap
Cores Threads
AMD Opteron 16 16
IBM Power7 ? ??
Intel Xeon 8 16

11. “By 2015 we will likely have over 100 cores on a many-
core processing chip in our notebook computers.”
- Computerworld

12. Welcome to the world of Multi-cores!

13. Q: How do we take advantage of
multi-core processors?

14. A: Concurrent Programming

15. #1 Threads & Locks

16. “Concurrency is hard. It involves a lot of problems that are very difficult
to think about and reason about and understand”
- Tim Bray co-inventor of XML

17. #1 Threads & Locks
• HARD to program
• HARD to scale
• Contentious

18. java.lang.IllegalArgumentException: Cannot determine primary key for entity ASCCarveout from row: {charge = 3027.00;
claimID = 321839138; }
! at com.webobjects.eoaccess.EODatabaseChannel._fetchObject(EODatabaseChannel.java:348)
! at com.webobjects.eoaccess.EODatabaseContext._objectsWithFetchSpecificationEditingContext
(EODatabaseContext.java:3071)
! at com.webobjects.eoaccess.EODatabaseContext.objectsWithFetchSpecification(EODatabaseContext.java:3195)
! at com.webobjects.eocontrol.EOObjectStoreCoordinator.objectsWithFetchSpecification(EOObjectStoreCoordinator.java:
488)
! at com.webobjects.eocontrol.EOEditingContext.objectsWithFetchSpecification(EOEditingContext.java:4069)
...Deadlock!
! at er.extensions.eof.ERXEC.objectsWithFetchSpecification(ERXEC.java:1211)
! at com.webobjects.eoaccess.EODatabaseContext.objectsForSourceGlobalID(EODatabaseContext.java:4084)
! at com.webobjects.eocontrol.EOObjectStoreCoordinator.objectsForSourceGlobalID(EOObjectStoreCoordinator.java:
634)
! at com.webobjects.eocontrol.EOEditingContext.objectsForSourceGlobalID(EOEditingContext.java:3923)
! at er.extensions.eof.ERXEC.objectsForSourceGlobalID(ERXEC.java:1169)
! at com.webobjects.eoaccess.EODatabaseContext._fireArrayFault(EODatabaseContext.java:4245)
! at com.webobjects.eoaccess.EOAccessArrayFaultHandler.completeInitializationOfObject
(EOAccessArrayFaultHandler.java:77)
! at com.webobjects.eocontrol._EOCheapCopyMutableArray.willRead(_EOCheapCopyMutableArray.java:37)
! at com.webobjects.eocontrol._EOCheapCopyMutableArray.count(_EOCheapCopyMutableArray.java:86)
! at com.mpv.evaluation.ClaimEvaluator.validateClaim(ClaimEvaluator.java:398)
! ...

19. BBC2, Top Gear - Series 15, Episode 1 - June 27 ’10

20. #2 Actor Model
(A Share NOTHING Model)

21. Slowmation

22. Demo

23. html5 <video>
<video poster="/slowmation/screenshots/0/2/4/425.jpg">
! <source type="video/ogg" src="/slowmation/videos/6/d/8/423.ogg" />
! <source type="video/mp4" src="/slowmation/videos/d/6/4/424.mp4" />
</video>

24. HTML5 Video Conversion
Thumbnail (.jpg)
Screenshot (.jpg)
Video (.mp4)
Video (.ogg)

25. Slowmation Actor
(Video Processor)
• actor ! THUMBNAIL
• actor ! GRAB
• actor ! CONVERT2H264
• actor ! CONVERT2OGG

26. !

27. Actor Messaging
• Asynchronous
• Non-blocking
• Immutable Messages
• NO shared data

28. Scala

29. Scala
• Immutable/Mutable datatypes
• Anonymous Functions (~Closures)
• No Static variables and methods
• Extensible

30. Scala
val greeting: String = “Hello World”;

31. Scala
val greeting = “Hello World”;

32. Scala
val greeting = “Hello World”

33. Scala
val greeting = “Hello World” // immutable
var response = new String() // mutable
response = “Hey!”

34. Java - Static Vars
public class _Talent extends EOGenericRecord {
public static final String ENTITY_NAME = "Talent";
}

35. Scala - Companion Object
object Talent extends EOGenericRecord {
val ENTITY_NAME = "Talent"
}

36. Thread-Safe

37. Scala - Pattern Matching
case a => {
...
}

38. Scala - Pattern Matching
try {
var epi: EditPageInterface = D2W.factory.editPageForNewObjectWithEntityNamed(entityName, session)
} catch {
case e: IllegalArgumentException => {
var epf: ErrorPageInterface = D2W.factory.errorPage(session)
epf.setMessage(e.toString)
}
}

39. Scala - Case Classes
case class PING
case class PONG

40. Scala - Case Classes
actor ! PING
actor ! PONG

41. Scala - Case Classes
case PING => {
...
}
case PONG => {
...
}

42. Scala - Anonymous Functions
x => x^2

43. Scala - Anonymous Functions
x, y => x + y

44. Scala - Anonymous Functions
x, y => {x + y}

45. Scala - Anonymous Functions
case (PING => {...})
case (PONG => {...})

46. λ - Expressions

47. Scala Actors - Example
case class THUMBNAIL(filepath: String) // Actor msg case class
val processor = actor {
loop {
react() {
case THUMBNAIL(filepath: String) => {
...
}
}
}
}
// asynchronous
processor ! THUMBNAIL(“/Library/WebServer/Documents/slowmation/screenshots/0/2/4/422.jpg”)

48. #2 Actor Model
• EASY to program
• Scalable
• NO Deadlocks!

49. Q: Why can Scala be used with WebObjects?

50. A: Scala compiles to Java Byte-code

51. WebObjects + Concurrency

52. Why?

53. Performance
• Exploit multi-core processors

54. Ajax
• More responsive UI

55. How?

56. Properties
WOAllowsConcurrentRequestHandling=true

57. Java - Synchronize Static Variables
private static String greeting = “Hello”; // private
public void setGreeting(String aGreeting) {
synchronized(greeting) { // synchronized block
greeting = aGreeting;
}
}

58. Free!

59. WO - What is Shared?
• Application
• Session (concurrent WO)

60. Use ERXEC
• Project Wonder
• Automatic lock/unlock handling

61. Properties
er.extensions.ERXEC.safeLocking=true

62. Debugging

63. Demo

64. Properties
-Dcom.sun.management.jmxremote=true
-Dcom.sun.management.jmxremote.authenticate=false
-Dcom.sun.management.jmxremote.ssl=false
// Specific port
-Dcom.sun.management.jmxremote.port=20102

65. Bottlenecks

66. EOF - Bottleneck
• Shared Object-cache
• Antithesis to Share Nothing
model
• Uses single database connection
• Single-Threaded

67. #3 STM
(Software Transactional Memory)

68. EOF + Scala
• DOESN’T work in Scala Actors!
•

69. Solutions
• Use Raw SQL
• Alternative database access
• Squeryl
• ...

70. Squeryl

71. Demo

72. Squeryl
• POSOs
• Actor Compatible
• Concurrent

73. “Scala as a concurrent programming language is
powerful, safe and easy-to-use”

74. Benchmarks

75. The Test
• ERWOAdaptor (Mina)
• WO Worker as Actor
• Apache bench
• c = 5...65
• n = 500

76. Results

77. Time per req. (mean)
200 ms
150 ms
100 ms
50 ms
0 ms
5 10 15 20 25 30 35 40 45 50 55 60 65
WOAdaptor ERWOScalaAdaptor ERWOAdaptor

78. Requests per second
800
600
400
200
0
5 10 15 20 25 30 35 40 45 50 55 60 65
WOAdaptor ERWOScalaAdaptor ERWOAdaptor

79. “Scala as a concurrent programming language is powerful,
safe and easy-to-use”

80. The R&D Imperative
In life long love
The key
Is R&D
The ladder of invention
Has eternal slide extension
Rung by rung
You’ll climb to heaven above.
Constant innovation
Guarantees a satiation
Of that ever changing want
And deepening need
Nourishment and care
To think anew…
Makes passions flair
And lets a culture breed
Between the sheets…
- by Emma Ahmad

81. Q&A

82. References
• What will YOU do with 100 cores?
http://www.computerworld.com.au/article/354261/
• WebObjects with Scala
http://wiki.objectstyle.org/confluence/display/WO/WebObjects+with+Scala
• Case Study: Slowmation
http://slowmation.uow.edu.au
• Source: ERWOScalaAdaptor
http://services.wocommunity.org/wowodc/ERWOScalaAdaptor