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Groovy 3之Native Lambda及Method/Constructor Reference

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  虽然Groovy 3 Alpha版本就已经支持Java 8的Lambda、Method Reference以及Constructor Reference全部语法，但从bytecode层面来看，其本质上依然是Closure及Method Pointer，换言之，只是语法上的兼容，但性能上并没有提升。而Groovy的性能常为人诟病，所以Groovy 2引入了静态编译，其编译出来的bytecode跟Java的相近，所以其性能逼近Java。为了延续静态编译的性能优势，Groovy核心团队决定在Groovy 3 Beta版本中实现Lambda、Method Reference以及Constructor Reference的Native版本，其语法不变，但生成的bytecode与Java的相似，这便是”Native”的由来。

  Groovy 3编译器会借助静态编译的类型推断以及Java 7引入的invokedynamic指令生成与Java相似的bytecode，但如果类型推断失败，那么生成的bytecode则与Closure及Method Pointer相同。需要注意一点的是，除了性能方面的考量，在设计和实现Native Lambda时还考虑了尽可能保留Closure既有特性，为此每个Native Lambda都会对应一个内部类实例，性能方面稍有影响。另外，从DSL角度来看，Native Lambda无法引用自身，也无法引用外层Native Lambda实例，所以Native Lambda相对Closure而言不太适合应用于DSL的实现。

示例

  下面提供一个简单例子来展示Native Lambda、Native Method Reference以及Native Constructor Reference的bytecode

NativeDemo的Groovy源码

import groovy.transform.CompileStatic

@CompileStatic
class NativeDemo {
    def nativeLambda() {
       [1, -2, 3].stream().map(e -> Math.abs(e)).toList()
    }
    def nativeMethodReference() {
       [1, -2, 3].stream().map(Math::abs).toList()
    }
    def nativeConstructorReference() {
       [1, -2, 3].stream().toArray(Integer[]::new)
    }
}

NativeDemo的bytecode

// class version 52.0 (52)
// access flags 0x21
public class NativeDemo implements groovy/lang/GroovyObject {

  // compiled from: script1617499378185.groovy
  // access flags 0x11
  public final INNERCLASS NativeDemo$_nativeLambda_lambda1 null _nativeLambda_lambda1

  // access flags 0x100A
  private static synthetic Lorg/codehaus/groovy/reflection/ClassInfo; $staticClassInfo

  // access flags 0x1089
  public static transient synthetic Z __$stMC

  // access flags 0x1082
  private transient synthetic Lgroovy/lang/MetaClass; metaClass

  // access flags 0x1
  public <init>()V
  @Lgroovy/transform/Generated;()
   L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
    ALOAD 0
    INVOKEVIRTUAL NativeDemo.$getStaticMetaClass ()Lgroovy/lang/MetaClass;
    ASTORE 1
    ALOAD 1
    ALOAD 0
    SWAP
    PUTFIELD NativeDemo.metaClass : Lgroovy/lang/MetaClass;
    ALOAD 1
    POP
   L1
    RETURN
    LOCALVARIABLE this LNativeDemo; L0 L1 0
    MAXSTACK = 2
    MAXLOCALS = 2

  // access flags 0x1
  public nativeLambda()Ljava/lang/Object;
   L0
    LINENUMBER 6 L0
    ICONST_3
    ANEWARRAY java/lang/Object
    DUP
    ICONST_0
    ICONST_1
    INVOKESTATIC java/lang/Integer.valueOf (I)Ljava/lang/Integer;
    AASTORE
    DUP
    ICONST_1
    BIPUSH -2
    INVOKESTATIC java/lang/Integer.valueOf (I)Ljava/lang/Integer;
    AASTORE
    DUP
    ICONST_2
    ICONST_3
    INVOKESTATIC java/lang/Integer.valueOf (I)Ljava/lang/Integer;
    AASTORE
    INVOKESTATIC org/codehaus/groovy/runtime/ScriptBytecodeAdapter.createList ([Ljava/lang/Object;)Ljava/util/List;
    INVOKEINTERFACE java/util/Collection.stream ()Ljava/util/stream/Stream; (itf)
    NEW NativeDemo$_nativeLambda_lambda1
    DUP
    LDC LNativeDemo;.class
    DUP
    INVOKESPECIAL NativeDemo$_nativeLambda_lambda1.<init> (Ljava/lang/Object;Ljava/lang/Object;)V
    INVOKEDYNAMIC apply(LNativeDemo$_nativeLambda_lambda1;)Ljava/util/function/Function; [
      // handle kind 0x6 : INVOKESTATIC
      java/lang/invoke/LambdaMetafactory.metafactory(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
      // arguments:
      (Ljava/lang/Object;)Ljava/lang/Object;, 
      // handle kind 0x5 : INVOKEVIRTUAL
      NativeDemo$_nativeLambda_lambda1.doCall(Ljava/lang/Integer;)Ljava/lang/Object;, 
      (Ljava/lang/Integer;)Ljava/lang/Object;
    ]
    INVOKEINTERFACE java/util/stream/Stream.map (Ljava/util/function/Function;)Ljava/util/stream/Stream; (itf)
    INVOKESTATIC org/codehaus/groovy/vmplugin/v8/PluginDefaultGroovyMethods.toList (Ljava/util/stream/Stream;)Ljava/util/List;
    ARETURN
   L1
    LOCALVARIABLE this LNativeDemo; L0 L1 0
    MAXSTACK = 5
    MAXLOCALS = 1

  // access flags 0x1
  public nativeMethodReference()Ljava/lang/Object;
   L0
    LINENUMBER 9 L0
    ICONST_3
    ANEWARRAY java/lang/Object
    DUP
    ICONST_0
    ICONST_1
    INVOKESTATIC java/lang/Integer.valueOf (I)Ljava/lang/Integer;
    AASTORE
    DUP
    ICONST_1
    BIPUSH -2
    INVOKESTATIC java/lang/Integer.valueOf (I)Ljava/lang/Integer;
    AASTORE
    DUP
    ICONST_2
    ICONST_3
    INVOKESTATIC java/lang/Integer.valueOf (I)Ljava/lang/Integer;
    AASTORE
    INVOKESTATIC org/codehaus/groovy/runtime/ScriptBytecodeAdapter.createList ([Ljava/lang/Object;)Ljava/util/List;
    INVOKEINTERFACE java/util/Collection.stream ()Ljava/util/stream/Stream; (itf)
    INVOKEDYNAMIC apply()Ljava/util/function/Function; [
      // handle kind 0x6 : INVOKESTATIC
      java/lang/invoke/LambdaMetafactory.metafactory(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
      // arguments:
      (Ljava/lang/Object;)Ljava/lang/Object;, 
      // handle kind 0x6 : INVOKESTATIC
      java/lang/Math.abs(I)I, 
      (Ljava/lang/Integer;)I
    ]
    INVOKEINTERFACE java/util/stream/Stream.map (Ljava/util/function/Function;)Ljava/util/stream/Stream; (itf)
    INVOKESTATIC org/codehaus/groovy/vmplugin/v8/PluginDefaultGroovyMethods.toList (Ljava/util/stream/Stream;)Ljava/util/List;
    ARETURN
   L1
    LOCALVARIABLE this LNativeDemo; L0 L1 0
    MAXSTACK = 4
    MAXLOCALS = 1

  // access flags 0x1
  public nativeConstructorReference()Ljava/lang/Object;
   L0
    LINENUMBER 12 L0
    ICONST_3
    ANEWARRAY java/lang/Object
    DUP
    ICONST_0
    ICONST_1
    INVOKESTATIC java/lang/Integer.valueOf (I)Ljava/lang/Integer;
    AASTORE
    DUP
    ICONST_1
    BIPUSH -2
    INVOKESTATIC java/lang/Integer.valueOf (I)Ljava/lang/Integer;
    AASTORE
    DUP
    ICONST_2
    ICONST_3
    INVOKESTATIC java/lang/Integer.valueOf (I)Ljava/lang/Integer;
    AASTORE
    INVOKESTATIC org/codehaus/groovy/runtime/ScriptBytecodeAdapter.createList ([Ljava/lang/Object;)Ljava/util/List;
    INVOKEINTERFACE java/util/Collection.stream ()Ljava/util/stream/Stream; (itf)
    INVOKEDYNAMIC apply()Ljava/util/function/IntFunction; [
      // handle kind 0x6 : INVOKESTATIC
      java/lang/invoke/LambdaMetafactory.metafactory(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
      // arguments:
      (I)Ljava/lang/Object;, 
      // handle kind 0x6 : INVOKESTATIC
      NativeDemo.ctorRef$nativeConstructorReference$0(I)[Ljava/lang/Integer;, 
      (I)[Ljava/lang/Integer;
    ]
    INVOKEINTERFACE java/util/stream/Stream.toArray (Ljava/util/function/IntFunction;)[Ljava/lang/Object; (itf)
    ARETURN
   L1
    LOCALVARIABLE this LNativeDemo; L0 L1 0
    MAXSTACK = 4
    MAXLOCALS = 1

  // access flags 0x1004
  protected synthetic $getStaticMetaClass()Lgroovy/lang/MetaClass;
    ALOAD 0
    INVOKEVIRTUAL java/lang/Object.getClass ()Ljava/lang/Class;
    LDC LNativeDemo;.class
    IF_ACMPEQ L0
    ALOAD 0
    INVOKESTATIC org/codehaus/groovy/runtime/ScriptBytecodeAdapter.initMetaClass (Ljava/lang/Object;)Lgroovy/lang/MetaClass;
    ARETURN
   L0
   FRAME SAME
    GETSTATIC NativeDemo.$staticClassInfo : Lorg/codehaus/groovy/reflection/ClassInfo;
    ASTORE 1
    ALOAD 1
    IFNONNULL L1
    ALOAD 0
    INVOKEVIRTUAL java/lang/Object.getClass ()Ljava/lang/Class;
    INVOKESTATIC org/codehaus/groovy/reflection/ClassInfo.getClassInfo (Ljava/lang/Class;)Lorg/codehaus/groovy/reflection/ClassInfo;
    DUP
    ASTORE 1
    PUTSTATIC NativeDemo.$staticClassInfo : Lorg/codehaus/groovy/reflection/ClassInfo;
   L1
   FRAME APPEND [org/codehaus/groovy/reflection/ClassInfo]
    ALOAD 1
    INVOKEVIRTUAL org/codehaus/groovy/reflection/ClassInfo.getMetaClass ()Lgroovy/lang/MetaClass;
    ARETURN
    MAXSTACK = 2
    MAXLOCALS = 2

  // access flags 0x1
  public getMetaClass()Lgroovy/lang/MetaClass;
  @Lgroovy/transform/Generated;()
  @Lgroovy/transform/Internal;()
  @Ljava/beans/Transient;()
    ALOAD 0
    GETFIELD NativeDemo.metaClass : Lgroovy/lang/MetaClass;
    DUP
    IFNULL L0
    ARETURN
   L0
   FRAME SAME1 groovy/lang/MetaClass
    POP
    ALOAD 0
    DUP
    INVOKEVIRTUAL NativeDemo.$getStaticMetaClass ()Lgroovy/lang/MetaClass;
    PUTFIELD NativeDemo.metaClass : Lgroovy/lang/MetaClass;
    ALOAD 0
    GETFIELD NativeDemo.metaClass : Lgroovy/lang/MetaClass;
    ARETURN
    MAXSTACK = 2
    MAXLOCALS = 1

  // access flags 0x1
  public setMetaClass(Lgroovy/lang/MetaClass;)V
  @Lgroovy/transform/Generated;()
  @Lgroovy/transform/Internal;()
    ALOAD 0
    ALOAD 1
    PUTFIELD NativeDemo.metaClass : Lgroovy/lang/MetaClass;
    RETURN
    MAXSTACK = 2
    MAXLOCALS = 2

  // access flags 0x101A
  private final static synthetic ctorRef$nativeConstructorReference$0(I)[Ljava/lang/Integer;
  @Lgroovy/transform/Generated;() // invisible
  @Lgroovy/transform/CompileStatic;() // invisible
   L0
    ILOAD 0
    MULTIANEWARRAY [Ljava/lang/Integer; 1
    ARETURN
   L1
    LOCALVARIABLE param0 I L0 L1 0
    MAXSTACK = 1
    MAXLOCALS = 1
}

NativeDemo$_nativeLambda_lambda1的bytecode（为Native Lambda而生成）

// class version 52.0 (52)
// access flags 0x31
public final class NativeDemo$_nativeLambda_lambda1 extends groovy/lang/Closure implements org/codehaus/groovy/runtime/GeneratedLambda {

  // compiled from: script1617499378185.groovy
  OUTERCLASS NativeDemo nativeLambda ()Ljava/lang/Object;
  // access flags 0x11
  public final INNERCLASS NativeDemo$_nativeLambda_lambda1 null _nativeLambda_lambda1

  // access flags 0x100A
  private static synthetic Lorg/codehaus/groovy/reflection/ClassInfo; $staticClassInfo

  // access flags 0x1089
  public static transient synthetic Z __$stMC

  // access flags 0x1
  public <init>(Ljava/lang/Object;Ljava/lang/Object;)V
   L0
    ALOAD 0
    ALOAD 1
    ALOAD 2
    INVOKESPECIAL groovy/lang/Closure.<init> (Ljava/lang/Object;Ljava/lang/Object;)V
   L1
    RETURN
    LOCALVARIABLE this LNativeDemo$_nativeLambda_lambda1; L0 L1 0
    LOCALVARIABLE _outerInstance Ljava/lang/Object; L0 L1 1
    LOCALVARIABLE _thisObject Ljava/lang/Object; L0 L1 2
    MAXSTACK = 3
    MAXLOCALS = 3

  // access flags 0x1
  // signature (Ljava/lang/Integer;)TR;
  // declaration: R doCall(java.lang.Integer)
  public doCall(Ljava/lang/Integer;)Ljava/lang/Object;
   L0
    LINENUMBER 6 L0
    ALOAD 1
    INVOKEVIRTUAL java/lang/Integer.intValue ()I
    INVOKESTATIC java/lang/Math.abs (I)I
    INVOKESTATIC java/lang/Integer.valueOf (I)Ljava/lang/Integer;
    ARETURN
   L1
    LINENUMBER 6 L1
   FRAME FULL [] [java/lang/Throwable]
    NOP
    ATHROW
   L2
    LOCALVARIABLE this LNativeDemo$_nativeLambda_lambda1; L0 L2 0
    LOCALVARIABLE e Ljava/lang/Integer; L0 L2 1
    MAXSTACK = 1
    MAXLOCALS = 2

  // access flags 0x1004
  protected synthetic $getStaticMetaClass()Lgroovy/lang/MetaClass;
    ALOAD 0
    INVOKEVIRTUAL java/lang/Object.getClass ()Ljava/lang/Class;
    LDC LNativeDemo$_nativeLambda_lambda1;.class
    IF_ACMPEQ L0
    ALOAD 0
    INVOKESTATIC org/codehaus/groovy/runtime/ScriptBytecodeAdapter.initMetaClass (Ljava/lang/Object;)Lgroovy/lang/MetaClass;
    ARETURN
   L0
   FRAME SAME
    GETSTATIC NativeDemo$_nativeLambda_lambda1.$staticClassInfo : Lorg/codehaus/groovy/reflection/ClassInfo;
    ASTORE 1
    ALOAD 1
    IFNONNULL L1
    ALOAD 0
    INVOKEVIRTUAL java/lang/Object.getClass ()Ljava/lang/Class;
    INVOKESTATIC org/codehaus/groovy/reflection/ClassInfo.getClassInfo (Ljava/lang/Class;)Lorg/codehaus/groovy/reflection/ClassInfo;
    DUP
    ASTORE 1
    PUTSTATIC NativeDemo$_nativeLambda_lambda1.$staticClassInfo : Lorg/codehaus/groovy/reflection/ClassInfo;
   L1
   FRAME APPEND [org/codehaus/groovy/reflection/ClassInfo]
    ALOAD 1
    INVOKEVIRTUAL org/codehaus/groovy/reflection/ClassInfo.getMetaClass ()Lgroovy/lang/MetaClass;
    ARETURN
    MAXSTACK = 2
    MAXLOCALS = 2
}