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Version 74.1 by Ravi Mendis on 2010/03/07 16:42
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1 Given that todays processors ship with dual or quad cores and server processors ship with between 8 to 32 cores, programs developed in languages like Java, Ruby, Groovy, Python and Perl are struggling to make use of all these cores. Scala, as its name suggests is built from the ground-up for [[concurrent programming>>http://en.wikipedia.org/wiki/Concurrent_computing]] - a methodology that can take advantage of these modern multi-core processors.
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3 If you use Scala for a concurrent programming application, the chances are that you're using Scala [[Actors>>http://en.wikipedia.org/wiki/Actor_model]] to do that.
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5 {{info title="Scala Actors"}}
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7 Concurrent programming in Scala is based on *Actors* (with an inbox) - a simple metaphor that is analogous to *Message Queues*.
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9 {{/info}}
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11 == Using Scala Actors with EOF ==
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13 EOF being notoriously single-threaded, is incredibly unsuitable for use with Scala Actors:
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15 * EOs are mutable objects and as such they cannot be passed safely into Scala Actors
16 * Fetching and updating EOs from within Scala Actors can cause [[deadlocks>>http://en.wikipedia.org/wiki/Deadlock]] with the WebObjects application
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18 Instead you can still use EOF but in a limited fashion - only to execute SQL.
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20 === Using EOAccess to execute SQL ===
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22 Use Wonder API: [[ERXEOAccessUtilities.evaluateSQLWithEntityNamed()>>http://webobjects.mdimension.com/hudson/job/Wonder53/javadoc/er/extensions/eof/ERXEOAccessUtilities.html#evaluateSQLWithEntity(com.webobjects.eocontrol.EOEditingContext,%20com.webobjects.eoaccess.EOEntity,%20java.lang.String)]]
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24 ==== Caveats ====
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26 If you're updating the state of EOs directly in the database using SQL from Scala Actors, you will subsequently need to refresh/refetch these EOs for the WebObjects application to see those changes.
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28 == EOF Alternatives ==
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30 You may also manipulate the database from outside the EOF stack.
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32 === Squeryl ===
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34 [[Squeryl>>http://max-l.github.com/Squeryl/index.html]] is a Scala internal [[Domain-specific language>>http://en.wikipedia.org/wiki/Domain-specific_language]] for database access (via SQL).
35 You may update the database from Scala Actors using Squeryl instead of using EOF. The advantage here is that you may access the database concurrently avoiding the single-threaded EOF bottleneck in your application.
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37 However the same caveat applies - you will need to refresh EOs in the EOF stack for the WebObjects application to reflect the changes made by Squeryl.