如何提高ClojureScript的性能

Question

我最近开始使用ClojureScript.当我将JavaScript程序重写为ClojureScript时,我担心ClojureScript的性能.

ClojureScript代码

(def NUM 10000)
(def data
  (vec (repeatedly NUM #(hash-map :x (rand) :y (rand)))))

(.time js/console "cljs")
(loop [x 0 y 0 d data]
  (if (empty? d)
    [x y]
    (recur (+ x (:x (first d)))
           (+ y (:y (first d)))
           (rest d))))
(.timeEnd js/console "cljs")

编译的JavaScript代码(优化:空白)

benchmark_cljs.benchmark.NUM = 1E4;
benchmark_cljs.benchmark.data = cljs.core.vec.call(null, cljs.core.repeatedly.call(null, benchmark_cljs.benchmark.NUM, function() {
  return cljs.core.PersistentHashMap.fromArrays.call(null, [new cljs.core.Keyword(null, "x", "x", 1013904362), new cljs.core.Keyword(null    , "y", "y", 1013904363)], [cljs.core.rand.call(null), cljs.core.rand.call(null)]);
}));
console.time("cljs");
var x_4753 = 0;
var y_4754 = 0;
var d_4755 = benchmark_cljs.benchmark.data;
while (true) {
  if (cljs.core.empty_QMARK_.call(null, d_4755)) {
    new cljs.core.PersistentVector(null, 2, 5, cljs.core.PersistentVector.EMPTY_NODE, [x_4753, y_4754], null);
  } else {
    var G__4756 = x_4753 + (new cljs.core.Keyword(null, "x", "x", 1013904362)).cljs$core$IFn$_invoke$arity$1(cljs.core.first.call(null, d    _4755));
    var G__4757 = y_4754 + (new cljs.core.Keyword(null, "y", "y", 1013904363)).cljs$core$IFn$_invoke$arity$1(cljs.core.first.call(null, d    _4755));
    var G__4758 = cljs.core.rest.call(null, d_4755);
    x_4753 = G__4756;
    y_4754 = G__4757;
    d_4755 = G__4758;
    continue;
  }
  break;
}
console.timeEnd("cljs");

JavaScript代码

var NUM = 10000;
var data = [];
for (var i = 0; i < NUM; i++) {
  data[i] = {
    x: Math.random(),
    y: Math.random()
  }
}
console.time('js');
var x = 0;
var y = 0;
for (var i = 0; i < data.length; i++) {
  x += data[i].x;
  y += data[i].y;
}
console.timeEnd('js');

ClojureScript代码和JavaScrpt代码执行相同的操作,但每个处理时间都不同.

处理时间

ClojureScript(optimizations :whitespace): 30 ? 70ms
ClojureScript(optimizations :advanced): 9 ? 13ms
JavaScript: 0.3ms ? 0.9ms

请告诉我如何改善ClojureScript的处理时间.

提前致谢.

Answer 1

您在ClojureScript中使用持久性数据结构,在JavaScript中使用可变数组和对象.可以预期两个片段的性能特征将是不同的.

现在,如果性能对您正在做的事情非常重要,并且持久性没有任何好处,您可以使用ClojureScript中的数组和对象:

(def NUM 10000)
(def data (array))
(loop [i 0]
  (when (< i NUM)
    (aset data i (js-obj "x" (js/Math.random) "y" (js/Math.random)))
    (recur (inc i))))

(let [lim (alength data)]
  (loop [x 0 y 0 i 0]
    (if (< i lim)
      (recur (+ x (aget data i "x"))
             (+ y (aget data i "y"))
             (inc i))
      (println x y))))

另一方面,如果你确实需要坚持所涉及的数据结构的旧版本,你可能会因为不必制作完整的副本来保存它们而赢回"失去的时间".

Answer 2

根据您需要多少性能以及您愿意放弃的内容,这里有多种选择.如果你有兴趣,我会在GitHub上放一些基准测试.

通过使用记录和本机字段访问,您可以将原始ClojureScript解决方案的运行时间减半:

(defrecord XY [x y])
(def data (mapv (fn [_] (XY. (rand) (rand))) (range NUM))) 

(defn sumXsAndYsWithLoopAndNativeFieldAccess [data]
  (loop [x 0 y 0 data data]
    (if (seq data)
      (let [o (first data)]
        (recur (+ x (.-x o)) (+ y (.-y o)) (rest data)))
      [x y])))

(time (sumXsAndYsWithLoopAndNativeFieldAccess data))

您还可以将数组用作可变本地,并获得解决方案的速度仅为本机JavaScript版本的8倍:

(defn sumsXsAndYsWithDotimesNativeFieldAccessAndMutableLocals [data]
  (let [x (doto (make-array 1)
            (aset 0 0))
        y (doto (make-array 1)
            (aset 0 0))]
    (dotimes [i (count data)]
      (let [o (data i)]
        (aset x 0 (+ (aget x 0) (.-x o)))
        (aset y 0 (+ (aget y 0) (.-y o)))))
    [(aget x 0) (aget y 0)]))

(time (sumsXsAndYsWithDotimesNativeFieldAccessAndMutableLocals data))

此外,您可以将上述内容与数组结合使用,并获得大约是本机JavaScript版本的3倍的解决方案:

(def data (into-array (mapv #(XY. (rand) (rand)) (range NUM))))

(defn sumsXsAndYsWithDotimesOnArrayNativeFieldAccessAndMutableLocals [data]
  (let [x (doto (make-array 1)
            (aset 0 0))
        y (doto (make-array 1)
            (aset 0 0))]
    (dotimes [i (alength data)]
      (let [o (aget data i)]
        (aset x 0 (+ (aget x 0) (.-x o)))
        (aset y 0 (+ (aget y 0) (.-y o)))))
    [(aget x 0) (aget y 0)]))

(time (sumsXsAndYsWithDotimesOnArrayNativeFieldAccessAndMutableLocals data))

您可能想查看David Nolen的Chambered项目.他有一些很好的宏来创建和更新本地变量,使上面的内容看起来不太荒谬.

无论如何,希望有所帮助.