javascript - java7/Rhino 中编译 javascript 与解释 javascript 的性能

Question

我很快就遇到了 Java7 中 Rhino javascript 引擎的性能问题 - 我的脚本(解析和编译文本)在 Chrome 中的运行速度比在 Java7 Rhino 脚本引擎中快 50-100 倍。

我试图找到改善情况的方法，发现 Rhino 支持脚本编译。我试着用我的脚本来做，但实际上没有看到任何改进。最后 - 我得到了一个虚拟的简短测试套件，我没有看到编译版本和解释版本之间的性能差异。请让我知道我做错了什么。

注意:一些消息来源提到 Rhino 引擎运行编译后的脚本比直接用 Java 编写的“相同”代码慢大约 1.6。不确定此示例中使用的“脚本编译”是否与假设的相同。

下面是测试 java 类和我在我的机器上从中得到的示例结果 ...

结果

     Running via com.sun.script.javascript.RhinoScriptEngine@c50443 ...       time: 886ms, chars: 38890, sum: 2046720      time: 760ms, chars: 38890, sum: 2046720      time: 725ms, chars: 38890, sum: 2046720      time: 765ms, chars: 38890, sum: 2046720      time: 742ms, chars: 38890, sum: 2046720       ... 3918ms     Running via com.sun.script.javascript.RhinoCompiledScript@b5c292 @ com.sun.script.javascript.RhinoScriptEngine@f92ab0 ...       time: 813ms, chars: 38890, sum: 2046720      time: 805ms, chars: 38890, sum: 2046720      time: 812ms, chars: 38890, sum: 2046720      time: 834ms, chars: 38890, sum: 2046720      time: 807ms, chars: 38890, sum: 2046720       ... 4101ms

Update after comment from Anon-Micro:

After wrapping invocation of the JavaScript eval() and compile() in test class into ...

import sun.org.mozilla.javascript.internal.Context;
try {
    Context cx = Context.enter();

    cx.setOptimizationLevel(9);
    cx.setLanguageVersion(170);

    ...
}
finally {
    Context.exit();
}

结果发生了显着变化——从平均 1.8(在新版本的测试类中)秒到 ~150 毫秒。然而，从通过 (CompiledScript = Compilable.compile()).eval(Bindings) -> Bindings.get("doTest") 加载的 ScriptEngine 中提取的 doTest() 函数实例仍然说它是 sun.org.mozilla.javascript.internal.InterpretedFunction 并且它的性能比从预编译字节码(Rhino 1.7r4)加载的 JS 版本稍差(大约 10%)——所以我仍然不是确定幕后实际发生的事情。

1800ms - ScriptEngine.eval(), Optimization Level = default(-1?)
1758ms - CompiledScript, Optimization Level = default(-1?)
 165ms - ScriptEngine.eval(), Optimization Level = 9
 132ms - CompiledScript, Optimization Level = 9
 116ms - compiled by Rhino 1.7r4 into bytecode class

PS:内部 sun 包中的 sun.org.mozilla.javascript.internal.Context 对我来说看起来是一个奇怪的设计 - “内部”表示假定此类不被开发人员使用，因此没有“认证” ' 在 Java 7 中操纵 JS 评估器优化级别的方法。

测试类(已更新，doTestCompiled从外部*.class加载)

import javax.script.Bindings;
import javax.script.Compilable;
import javax.script.CompiledScript;
import javax.script.Invocable;
import javax.script.ScriptContext;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.SimpleScriptContext;
import sun.org.mozilla.javascript.internal.Context;
import sun.org.mozilla.javascript.internal.Scriptable;
import sun.org.mozilla.javascript.internal.Function;

public class RhinoPerfTest4 {

    final static ScriptEngineManager scm = new ScriptEngineManager();
    final static String TEST_SCRIPT1 =
            "function doTest() {\n"
            + "    var scale = 5000, i, a = [], str, l, sum = 0,\n"
            + "        start = (new Date()).getTime(), end;\n"
            + "    for( i = 0; i < scale; i++ )\n"
            + "        a.push(\"\" + i);\n"
            + "    str = a.join(\"\");\n"
            + "    l = str.length;\n"
            + "    for( i = 0; i < l; i++ ) {\n"
            + "        var c = str.charCodeAt(i);\n"
            + "        if( c > 0)\n"
            + "            sum += c;\n"
            + "    }\n"
            + "    end = (new Date()).getTime();\n"
            + "\n"
            + "    // print(\" time: \" + (end - start) "
            + "          + \"ms, chars: \" + l "
            + "          + \", sum: \" + sum + \"\\n\");\n"
            + "}\n";
    final static String TEST_SCRIPT2 =
            "function doTest() {\n"
            + "    var a = [], i;\n"
            + "    for( i = 0; i < 500; i++ ) a.push(1);\n"
            + "}\n";

    static class TestSet {

        public int nCycles;
        public String script;

        public TestSet(int nCycles, String script) {
            this.nCycles = nCycles;
            this.script = script;
        }
    }
    static TestSet set1 = new TestSet(5, TEST_SCRIPT1);
    static TestSet set2 = new TestSet(500, TEST_SCRIPT2);

    public static void main(String[] args) throws Exception {
        ScriptEngine se;
        int i;
        long ts, te;
        TestSet set = set1;
        Object noArgs[] = new Object[]{};

        try {
            org.mozilla.javascript.Context mctx = org.mozilla.javascript.Context.enter();

            se = scm.getEngineByExtension("js");
            doTestCompiled doTestPreCompiled = new doTestCompiled();
            org.mozilla.javascript.Scriptable scope = mctx.initStandardObjects();

            doTestPreCompiled.call(mctx, scope, scope, null);
            org.mozilla.javascript.Function doTest = 
                    (org.mozilla.javascript.Function)scope.get("doTest", null);

            for( int nHotSpot = 0; nHotSpot < 5; nHotSpot++ ) {
                if( nHotSpot > 0 )
                    Thread.sleep(500);

                ts = System.currentTimeMillis();
                for( i = 0; i < set.nCycles; i++ ) {
                    doTest.call(mctx, scope, null, null);
                }
                te = System.currentTimeMillis();
                System.out.println("  " + nHotSpot + ": " + (te - ts) + "ms");
            }
        }
        finally {
            org.mozilla.javascript.Context.exit();
        }


        for( int nOpt = 0; nOpt < 2; nOpt++ ) {
            if( nOpt > 0 )
                Thread.sleep(500);

            Context cx = null;

            try {
                System.out.println("Cycle: " + nOpt);

                cx = Context.enter();
                if( nOpt > 0 ) {
                    System.out.println("OptLevel: " + 9);
                    cx.setOptimizationLevel(9);
                    cx.setLanguageVersion(170);
                }

                se = scm.getEngineByExtension("js");
                se.eval(set.script);
                System.out.println("\nRunning via " + se + " ... ");

                Invocable invocable = (Invocable) se;

                for( int nHotSpot = 0; nHotSpot < 5; nHotSpot++ ) {
                    if( nHotSpot > 0 )
                        Thread.sleep(500);

                    ts = System.currentTimeMillis();
                    for( i = 0; i < set.nCycles; i++ ) {
                        invocable.invokeFunction("doTest", noArgs);
                    }
                    te = System.currentTimeMillis();
                    System.out.println("  " + nHotSpot + ": " + (te - ts) + "ms");
                }

                se = scm.getEngineByExtension("js");
                Compilable cse = (Compilable) se;
                CompiledScript cs = cse.compile(set.script/* + "(doTest())"*/);
                Scriptable scope = cx.initStandardObjects();

                ScriptContext scriptContext = new SimpleScriptContext();
                Bindings vars = scriptContext.getBindings(ScriptContext.ENGINE_SCOPE);

                cs.eval(vars);

                Object odoTest = scriptContext.getAttribute("doTest");
                Function doTest = (Function) vars.get("doTest");

                System.out.println("\nRunning via " + cs + " @ " + se + " ... ");

                for( int nHotSpot = 0; nHotSpot < 5; nHotSpot++ ) {
                    if( nHotSpot > 0 )
                        Thread.sleep(500);

                    ts = System.currentTimeMillis();
                    for( i = 0; i < set.nCycles; i++ ) {
                        doTest.call(cx, scope, null, noArgs);
                    }
                    te = System.currentTimeMillis();
                    System.out.println("  " + nHotSpot + ": " + (te - ts) + "ms");
                }

            }
            finally {
                if( cx != null )
                    Context.exit();
            }
        }
    }
}

Answer 1

Rhino 引擎实际上能够“在进程中”将脚本编译成字节码，因此您无需先运行该工具来生成 .class 文件。您只需要设置“优化级别”，引擎就会在执行脚本之前自动预编译脚本。覆盖优化级别的一种方法是使用 VM 参数 -Drhino.opt.level。将其设置为 0 到 9 之间的任何值并运行您的原始测试程序，您应该会看到更好的性能。

顺便说一句，这与您提到的编译工具使用的优化设置相同。 https://developer.mozilla.org/en-US/docs/Rhino/Optimization

要完全控制程序中的优化级别和 javascript 版本，您可以执行以下操作。然而，你失去了一些 RhinoScriptEngine 类(它只是一个环境包装器而不是 javascript 引擎)提供的修饰。一种这样的修整是“打印”功能，它实际上是由所述包装器注入(inject)的。出于测试目的，您可以将“print”替换为“java.lang.System.out.print”。

    int optimisationLevel = 3;
    int languageVersion = Context.VERSION_1_7;

    try {
        Context cx = Context.enter();
        cx.setOptimizationLevel(optimisationLevel);
        cx.setLanguageVersion(languageVersion);

        ImporterTopLevel scope = new ImporterTopLevel(cx);
        cx.evaluateString(scope, TEST_SCRIPT1, "doTest", 1, null);

        for (int i = 0; i < 10; i++)
            cx.evaluateString(scope, "doTest();", "", 1, null);

    } finally {
        Context.exit();
    }

您提到了以下内容:

Note: some sources mention that Rhino engine runs compiled script roughly 1.6 slower than the "same" code written directly in Java. Not sure if "compilation of script" used in this sample the is same one which is supposed there.

我会对报告此问题的来源感兴趣，我在 Java 中的斐波那契函数花费的时间大约是编译后的 js 实现时间的 1/30。但也许我遗漏了什么。