Painless: Optimize instance creation in LambdaBootstrap (#24618)
Optimize instance creation in LambdaBootstrap to allow Hotspot's escape analysis, preventing us from creating many instances stressing GC
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@ -38,6 +38,7 @@ import java.security.PrivilegedAction;
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import static java.lang.invoke.MethodHandles.Lookup;
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import static org.elasticsearch.painless.Compiler.Loader;
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import static org.elasticsearch.painless.WriterConstants.CLASS_VERSION;
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import static org.elasticsearch.painless.WriterConstants.CTOR_METHOD_NAME;
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import static org.elasticsearch.painless.WriterConstants.DELEGATE_BOOTSTRAP_HANDLE;
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import static org.objectweb.asm.Opcodes.ACC_FINAL;
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import static org.objectweb.asm.Opcodes.ACC_PRIVATE;
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@ -89,9 +90,13 @@ import static org.objectweb.asm.Opcodes.H_NEWINVOKESPECIAL;
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* public static final class $$Lambda0 implements Consumer {
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* private List arg$0;
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*
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* public $$Lambda0(List arg$0) {
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* private $$Lambda0(List arg$0) {
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* this.arg$0 = arg$0;
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* }
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*
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* public static Consumer create$lambda(List arg$0) {
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* return new $$Lambda0(arg$0);
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* }
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*
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* public void accept(Object val$0) {
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* Painless$Script.lambda$0(this.arg$0, val$0);
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@ -120,10 +125,17 @@ import static org.objectweb.asm.Opcodes.H_NEWINVOKESPECIAL;
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* on whether or not there are captures. If there are no captures
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* the same instance of the generated lambda class will be
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* returned each time by the factory method as there are no
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* changing values other than the arguments. If there are
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* captures a new instance of the generated lambda class will
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* be returned each time with the captures passed into the
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* changing values other than the arguments, the lambda is a singleton.
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* If there are captures, a new instance of the generated lambda class
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* will be returned each time with the captures passed into the
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* factory method to be stored in the member fields.
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* Instead of calling the ctor, a static factory method is created
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* in the lambda class, because a method handle to the ctor directly
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* is (currently) preventing Hotspot optimizer from correctly doing
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* escape analysis. Escape analysis is important to optimize the
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* code in a way, that a new instance is not created on each lambda
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* invocation with captures, stressing garbage collector (thanks
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* to Rémi Forax for the explanation about this on Jaxcon 2017!).
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*/
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public final class LambdaBootstrap {
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@ -153,6 +165,11 @@ public final class LambdaBootstrap {
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*/
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private static final String DELEGATED_CTOR_WRAPPER_NAME = "delegate$ctor";
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/**
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* This method name is used to generate the static factory for capturing lambdas.
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*/
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private static final String LAMBDA_FACTORY_METHOD_NAME = "create$lambda";
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/**
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* Generates a lambda class for a lambda function/method reference
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* within a Painless script. Variables with the prefix interface are considered
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@ -198,7 +215,8 @@ public final class LambdaBootstrap {
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// Handles the special case where a method reference refers to a ctor (we need a static wrapper method):
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if (delegateInvokeType == H_NEWINVOKESPECIAL) {
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generateStaticCtorDelegator(cw, delegateClassType, delegateMethodName, delegateMethodType);
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assert CTOR_METHOD_NAME.equals(delegateMethodName);
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generateStaticCtorDelegator(cw, ACC_PRIVATE, DELEGATED_CTOR_WRAPPER_NAME, delegateClassType, delegateMethodType);
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// replace the delegate with our static wrapper:
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delegateMethodName = DELEGATED_CTOR_WRAPPER_NAME;
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delegateClassType = lambdaClassType;
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@ -281,16 +299,15 @@ public final class LambdaBootstrap {
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MethodType factoryMethodType,
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Capture[] captures) {
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String conName = "<init>";
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String conDesc = factoryMethodType.changeReturnType(void.class).toMethodDescriptorString();
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Method conMeth = new Method(conName, conDesc);
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Method conMeth = new Method(CTOR_METHOD_NAME, conDesc);
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Type baseConType = Type.getType(Object.class);
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Method baseConMeth = new Method(conName,
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Method baseConMeth = new Method(CTOR_METHOD_NAME,
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MethodType.methodType(void.class).toMethodDescriptorString());
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int modifiers = ACC_PUBLIC;
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int modifiers = (captures.length > 0) ? ACC_PRIVATE : ACC_PUBLIC;
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GeneratorAdapter constructor = new GeneratorAdapter(modifiers, conMeth,
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cw.visitMethod(modifiers, conName, conDesc, null, null));
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cw.visitMethod(modifiers, CTOR_METHOD_NAME, conDesc, null, null));
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constructor.visitCode();
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constructor.loadThis();
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constructor.invokeConstructor(baseConType, baseConMeth);
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@ -304,21 +321,31 @@ public final class LambdaBootstrap {
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constructor.returnValue();
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constructor.endMethod();
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// Add a factory method, if lambda takes captures.
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// @uschindler says: I talked with Rémi Forax about this. Technically, a plain ctor
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// and a MethodHandle to the ctor would be enough - BUT: Hotspot is unable to
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// do escape analysis through a MethodHandles.findConstructor generated handle.
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// Because of this we create a factory method. With this factory method, the
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// escape analysis can figure out that everything is final and we don't need
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// an instance, so it can omit object creation on heap!
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if (captures.length > 0) {
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generateStaticCtorDelegator(cw, ACC_PUBLIC, LAMBDA_FACTORY_METHOD_NAME, lambdaClassType, factoryMethodType);
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}
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}
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/**
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* Generates a factory method to delegate to constructors using
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* {@code INVOKEDYNAMIC} using the {@link #delegateBootstrap} type converter.
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* Generates a factory method to delegate to constructors.
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*/
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private static void generateStaticCtorDelegator(ClassWriter cw, Type delegateClassType, String delegateMethodName,
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MethodType delegateMethodType) {
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Method wrapperMethod = new Method(DELEGATED_CTOR_WRAPPER_NAME, delegateMethodType.toMethodDescriptorString());
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private static void generateStaticCtorDelegator(ClassWriter cw, int access, String delegatorMethodName,
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Type delegateClassType, MethodType delegateMethodType) {
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Method wrapperMethod = new Method(delegatorMethodName, delegateMethodType.toMethodDescriptorString());
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Method constructorMethod =
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new Method(delegateMethodName, delegateMethodType.changeReturnType(void.class).toMethodDescriptorString());
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int modifiers = ACC_PRIVATE | ACC_STATIC;
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new Method(CTOR_METHOD_NAME, delegateMethodType.changeReturnType(void.class).toMethodDescriptorString());
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int modifiers = access | ACC_STATIC;
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GeneratorAdapter factory = new GeneratorAdapter(modifiers, wrapperMethod,
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cw.visitMethod(modifiers, DELEGATED_CTOR_WRAPPER_NAME, delegateMethodType.toMethodDescriptorString(), null, null));
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cw.visitMethod(modifiers, delegatorMethodName, delegateMethodType.toMethodDescriptorString(), null, null));
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factory.visitCode();
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factory.newInstance(delegateClassType);
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factory.dup();
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@ -329,7 +356,8 @@ public final class LambdaBootstrap {
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}
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/**
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* Generates the interface method that will delegate (call) to the delegate method.
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* Generates the interface method that will delegate (call) to the delegate method
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* with {@code INVOKEDYNAMIC} using the {@link #delegateBootstrap} type converter.
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*/
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private static void generateInterfaceMethod(
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ClassWriter cw,
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@ -464,8 +492,7 @@ public final class LambdaBootstrap {
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try {
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return new ConstantCallSite(
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lookup.findConstructor(lambdaClass, factoryMethodType.changeReturnType(void.class))
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.asType(factoryMethodType));
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lookup.findStatic(lambdaClass, LAMBDA_FACTORY_METHOD_NAME, factoryMethodType));
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} catch (ReflectiveOperationException exception) {
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throw new IllegalStateException("unable to create lambda class", exception);
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}
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@ -53,8 +53,10 @@ public final class WriterConstants {
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public static final String CLASS_NAME = BASE_CLASS_NAME + "$Script";
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public static final Type CLASS_TYPE = Type.getObjectType(CLASS_NAME.replace('.', '/'));
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public static final String CTOR_METHOD_NAME = "<init>";
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public static final Method CONSTRUCTOR = getAsmMethod(void.class, "<init>", String.class, String.class, BitSet.class);
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public static final Method CONSTRUCTOR = getAsmMethod(void.class, CTOR_METHOD_NAME, String.class, String.class, BitSet.class);
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public static final Method CLINIT = getAsmMethod(void.class, "<clinit>");
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// All of these types are caught by the main method and rethrown as ScriptException
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@ -162,7 +164,7 @@ public final class WriterConstants {
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public static final Type STRING_TYPE = Type.getType(String.class);
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public static final Type STRINGBUILDER_TYPE = Type.getType(StringBuilder.class);
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public static final Method STRINGBUILDER_CONSTRUCTOR = getAsmMethod(void.class, "<init>");
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public static final Method STRINGBUILDER_CONSTRUCTOR = getAsmMethod(void.class, CTOR_METHOD_NAME);
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public static final Method STRINGBUILDER_APPEND_BOOLEAN = getAsmMethod(StringBuilder.class, "append", boolean.class);
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public static final Method STRINGBUILDER_APPEND_CHAR = getAsmMethod(StringBuilder.class, "append", char.class);
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public static final Method STRINGBUILDER_APPEND_INT = getAsmMethod(StringBuilder.class, "append", int.class);
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