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Motivation

Need ability to invoke tasks asynchronously at the bottom of core.async. And fast.

Goals

  • Executor interface
    • Need ability to invoke tasks asynchronously
      • Effectively ExecutorService.submit(Runnable)
    • May want ability to shutdown the executor?
  • Executor implementation(s)
    • Need some implementation to cover JDK 1.6, 1.7, 1.8
    • Possible implementations
      • ThreadPoolExecutor
      • ForkJoin 
    • Executor library version
      • Provide implementation without external dependency
        • Use what's in the JDK or
        • Repackage jsr166 into our own package (jsr166 is public domain)
      • Allow path for users to use a bleeding edge version
    • Configuration 
      • Both ThreadPoolExecutor and ForkJoin have a number of of possible configuration parameters
      • Provide good defaults but also let user change them

Non-goals

  • Do not need to provide general access to ForkJoin (fork, join, recursive computation, etc)
  • Do not need access to futures for tasks
  • Do not need task cancellation

Proposed solution

  • Define protocol for async task execution
    • (defprotocol Executor (exec `[e task]))
  • Provide several implementations
    • for ThreadPoolExecutor
    • for ForkJoinPool 
      • Repackage jsr166y into our own packages
      • Allow user to use jsr166e instead
  • Choose default implementation based on environment
    • Simplest: always use our own jsr166y version
    • Or possibly (for JDK 1.8): use java.util.concurrent.ForkJoinPool (effectively jsr166e)
  • Allow user to override the implementation we chose

 

Clojure
version 
JDK
version 
Executor
choice #1 
Executor
choice #2 
1.51.6jsr166 jarExecutor
1.51.7  
1.51.8???  
1.61.6Clojure jsr166y 
1.61.7Clojure jsr166y 
1.61.8juc ForkJoin (jsr166e) 

Here:

  • jsr166 jar = external jsr166 jar (might be either y for JDK 1.6+ or e for JDK 1.7+)
  • Clojure jsr166y = Clojure re-packaged version of jsr166y code, included in Clojure 1.6+
  • juc ForkJoin = java.util.concurrent version of ForkJoin
  • Executor = java.util.concurrent Executor

Background / Reference

Background:

  • JSR 166 
    • jsr166x - included in JDK 1.6, does not contain ForkJoin
    • jsr166y - compiled with JDK 1.6, included in JDK 1.7. jsr166y jar has fixes past what is in the JDK 1.6.
    • jsr166e - compiled with JDK 1.8, to be included in JDK 1.8. jsr166e jar has fixes past what is in JDK 1.7. 
  • Scala solution
    • Repackage known version of jsr166y as scala.concurrent and include in the Scala language (Akka makes use of it from there)
      • Covers JDK 1.6+ (good) but does not contain the very latest updates for JDK 1.8 that are in jsr166e (bad)
      • When they have a version of Scala that requires JDK 1.7, they will presumably update to jsr166e
    • Akka has pluggable executor providers and using a custom one allows you to make use of jsr166e if you need it
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