Compile-time dispatch usage of jsr166y vs. bundled FJ.

Signed-off-by: Rich Hickey <richhickey@gmail.com>

Author: tsdh

src/clj/clojure/core/reducers.clj

@@ -20,21 +20,52 @@
 (set! *warn-on-reflection* true)
 
 ;;;;;;;;;;;;;; some fj stuff ;;;;;;;;;;
-;;todo - dynamic java 7+ detection and use
 
-(def pool (delay (jsr166y.ForkJoinPool.)))
+(defmacro ^:private compile-if
+  "Evaluate `exp` and if it returns logical true and doesn't error, expand to
+  `then`.  Else expand to `else`.
 
-(defn fjtask [^Callable f]
-  (jsr166y.ForkJoinTask/adapt f))
+  (compile-if (Class/forName \"java.util.concurrent.ForkJoinTask\")
+    (do-cool-stuff-with-fork-join)
+    (fall-back-to-executor-services))"
+  [exp then else]
+  (if (try (eval exp)
+           (catch Throwable _ false))
+    `(do ~then)
+    `(do ~else)))
 
-(defn- fjinvoke [f]
-  (if (jsr166y.ForkJoinTask/inForkJoinPool)
-    (f)
-    (.invoke ^jsr166y.ForkJoinPool @pool ^jsr166y.ForkJoinTask (fjtask f))))
+(compile-if
+ (Class/forName "java.util.concurrent.ForkJoinTask")
+ ;; We're running a JDK 7+
+ (do
+   (def pool (delay (java.util.concurrent.ForkJoinPool.)))
 
-(defn- fjfork [task] (.fork ^jsr166y.ForkJoinTask task))
+   (defn fjtask [^Callable f]
+     (java.util.concurrent.ForkJoinTask/adapt f))
 
-(defn- fjjoin [task] (.join ^jsr166y.ForkJoinTask task))
+   (defn- fjinvoke [f]
+     (if (java.util.concurrent.ForkJoinTask/inForkJoinPool)
+       (f)
+       (.invoke ^java.util.concurrent.ForkJoinPool @pool ^java.util.concurrent.ForkJoinTask (fjtask f))))
+
+   (defn- fjfork [task] (.fork ^java.util.concurrent.ForkJoinTask task))
+
+   (defn- fjjoin [task] (.join ^java.util.concurrent.ForkJoinTask task)))
+ ;; We're running a JDK <6
+ (do
+   (def pool (delay (jsr166y.ForkJoinPool.)))
+
+   (defn fjtask [^Callable f]
+     (jsr166y.ForkJoinTask/adapt f))
+
+   (defn- fjinvoke [f]
+     (if (jsr166y.ForkJoinTask/inForkJoinPool)
+       (f)
+       (.invoke ^jsr166y.ForkJoinPool @pool ^jsr166y.ForkJoinTask (fjtask f))))
+
+   (defn- fjfork [task] (.fork ^jsr166y.ForkJoinTask task))
+
+   (defn- fjjoin [task] (.join ^jsr166y.ForkJoinTask task))))
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (defn reduce
@@ -214,7 +245,7 @@
      clojure.core.protocols/CollReduce
      (coll-reduce [this f1] (clojure.core.protocols/coll-reduce this f1 (f1)))
      (coll-reduce [_  f1 init] (clojure.core.protocols/coll-reduce coll (rf f1) init))
-     
+
      CollFold
      (coll-fold [_ n combinef reducef] (coll-fold coll n combinef (rf reducef))))))
 
@@ -225,7 +256,7 @@
 
   clojure.lang.Seqable
   (seq [_] (concat (seq left) (seq right)))
-  
+
   clojure.core.protocols/CollReduce
   (coll-reduce [this f1] (clojure.core.protocols/coll-reduce this f1 (f1)))
   (coll-reduce
@@ -309,7 +340,7 @@
   [coll n combinef reducef]
   ;;can't fold, single reduce
   (reduce reducef (combinef) coll))
- 
+
  clojure.lang.IPersistentVector
  (coll-fold
   [v n combinef reducef]
@@ -319,4 +350,3 @@
  (coll-fold
   [m n combinef reducef]
   (.fold m n combinef reducef fjinvoke fjtask fjfork fjjoin)))
-