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  • Define protocol for async task execution
    • (defprotocol Executor (exec `[e task]))
  • Provide several implementations
    • for ThreadPoolExecutor
    • for ForkJoinPool 
      • Repackage jsr166y into our own packages (put in Clojure 1.6)
      • Allow user to use jsr166e instead?
      • Use built-in JDK version
  • The general ordering of "bestness" is:
    • JDK 1.6:  jsr166y jsr166y >> Clojure ForkJoinPool >> ThreadPoolExecutor
    • JDK 1.7: jsr166e >> jsr166y >> Clojure ForkJoinPool >> JDK ForkJoinPool
    • JDK 1.8: jsr166e >> JDK ForkJoinPool
  • A possible ordering that works for everything but JDK 1.8 (where it merely does ok things by default):
    • jsr166e >> jsr166y >> Clojure ForkJoinPool >> JDK ForkJoinPool >> ThreadPoolExecutor
    • Choose default implementation based on environment - try these in order, choosing first one that works:
      • Check for jsr166e.ForkJoinPool (external JDK version) - allow override, JDK 1.7+
      • Check for jsr166y.ForkJoinPool (external JDK version) - allow override, JDK 1.6+
      • Check for clojure.concurrent.ForkJoinPool (Clojure repackaged jsr166y) - always available in Clojure 1.6+
      • Check for java.util.concurrent.ForkJoinPool (JDK built-in version) - always available in JDK 1.7+
      • Fallback to Executor version - always available in JDK 1.6+
  • Allow user to override the implementation we chose with their own custom executor that does whatever they want

Table of what version you'll get depending on your environment based on the ordering rules above:

Clojure versionJDK versionExternal jarWhatcha getNotes ForkJoinPool 1.6 can't use jsr166e! ForkJoinPool ForkJoinPool ForkJoinPool ForkJoinPool ForkJoinPool ForkJoinPool 
1.61.6noneClojure ForkJoinPool 
1.61.6jsr166yjsr166y ForkJoinPool 
1.61.6jsr166eClojure ForkJoinPoolJDK 1.6 can't use jsr166e!
1.61.7noneClojure ForkJoinPool 
1.61.7jsr166yjsr166y ForkJoinPool 
1.61.7jsr166ejsr166e ForkJoinPool 
1.61.8noneClojure JDK ForkJoinPoolJDK would be better? 
1.61.8jsr166yjsr166yJDK ForkJoinPoolJDK would be better but this is a weird case.1.8 is better than jsr166y here
1.61.8jsr166ejsr166e ForkJoinPool