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Continuations And Java

This presentation covers the concept of continuations, which allow a programming language to save and restore the execution state at any point. We will explore why continuations are advantageous, including simplifying asynchronous code, improving performance over traditional threading, and aiding in functional programming. Implementations in Java will be discussed, featuring libraries such as Jetty Continuations and JavaFlow, as well as frameworks like Kilim. Learn how continuations can streamline complex asynchronous interactions and the principles behind their functionality.

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Continuations And Java

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  1. Continuations And Java Regis - xu.regis@gmail.com

  2. Agenda • What is Continuations • Why Continuations • Implementations in Java • Jetty Continuations API • JavaFlow • Kilim • JVM Continuations

  3. What is Continuations • Definition from wikipedia: • Give a programming language the ability to save the execution state at any point and return to that point at alter point in the program • Basic characteristics: • Local data (variables, ...) is restored on successive calls. • Execution of a coroutine is only suspended when it yields, to be resumed when the coroutine is called again.

  4. started! 0 returned a continuation 1 returned another continuation

  5. Why Continuations • Thread is heavy and expensive • Writing asynchronous code in the synchronous style • Supporting functional languages • SAX parser • Web servers • linearize complex interactions • “back button” problem

  6. Implemented As Library • Jetty 6.0 • For resolving AJAX polling problem • Event based + retry

  7. Implemented As Library (Cont.) • Instrumentation byte code • Save current stack frames • Store local variables • Save PC • Restore stack trace • goto + switch table

  8. From A Thread of One’s Own

  9. Implemented As Library (Cont.) • Implementations • JavaFlow • Asymmetric coroutines: each yield needs to specify which coroutine should come next. • Kilim • Symmetric coroutines: a scheduler decides which coroutine should run next after a yield. • Framework has a thread pool and decide which coroutine run on which thread. • RIFE/Continuations (WebWork)

  10. Implemented In JVM • Support save and restore stack frames by JVM • No instrumentation needed • APIs is similar with library provided

  11. References • http://wiki.jvmlangsummit.com/JVM_Continuations • http://classparser.blogspot.com/2010/01/coroutines.html • http://lambda-the-ultimate.org/node/1002 • http://sourceforge.net/projects/jauvm/ • http://commons.apache.org/sandbox/javaflow/ • http://rifers.org/wiki/display/RIFECNT/Home • http://www.artima.com/lejava/articles/continuations.html • A Thread of One’s Own • Lazy Continuations for Java Virtual Machines

  12. Question?

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