Mercurial > jdk8-mips64-public > nashorn / file revision

 /*

  * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.  Oracle designates this

  * particular file as subject to the "Classpath" exception as provided

  * by Oracle in the LICENSE file that accompanied this code.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 package jdk.nashorn.internal.runtime;

 import static jdk.nashorn.internal.lookup.Lookup.MH;

 import static jdk.nashorn.internal.runtime.ECMAErrors.typeError;

 import static jdk.nashorn.internal.runtime.ScriptRuntime.UNDEFINED;

 import java.lang.invoke.MethodHandle;

 import java.lang.invoke.MethodHandles;

 import java.lang.invoke.MethodType;

 import jdk.nashorn.internal.runtime.linker.JavaAdapterFactory;

 /**

  * A container for data needed to instantiate a specific {@link ScriptFunction} at runtime.

  * Instances of this class are created during codegen and stored in script classes'

  * constants array to reduce function instantiation overhead during runtime.

  */

 public abstract class ScriptFunctionData {

     /** Name of the function or "" for anonynous functions */

     protected final String name;

     /** All versions of this function that have been generated to code */

     protected final CompiledFunctions code;

     private int arity;

     private final boolean isStrict;

     private final boolean isBuiltin;

     private final boolean isConstructor;

     private static final MethodHandle NEWFILTER     = findOwnMH("newFilter", Object.class, Object.class, Object.class);

     private static final MethodHandle BIND_VAR_ARGS = findOwnMH("bindVarArgs", Object[].class, Object[].class, Object[].class);

     /**

      * Constructor

      *

      * @param name          script function name

      * @param arity         arity

      * @param isStrict      is the function strict

      * @param isBuiltin     is the function built in

      * @param isConstructor is the function a constructor

      */

     protected ScriptFunctionData(final String name, final int arity, final boolean isStrict, final boolean isBuiltin, final boolean isConstructor) {

         this.name          = name;

         this.arity         = arity;

         this.code          = new CompiledFunctions();

         this.isStrict      = isStrict;

         this.isBuiltin     = isBuiltin;

         this.isConstructor = isConstructor;

     }

     final int getArity() {

         return arity;

     }

     /**

      * Used from e.g. Native*$Constructors as an explicit call. TODO - make arity immutable and final

      * @param arity new arity

      */

     void setArity(final int arity) {

         this.arity = arity;

     }

     CompiledFunction bind(final CompiledFunction originalInv, final ScriptFunction fn, final Object self, final Object[] args) {

         final MethodHandle boundInvoker = bindInvokeHandle(originalInv.getInvoker(), fn, self, args);

         //TODO the boundinvoker.type() could actually be more specific here

         if (isConstructor()) {

             ensureConstructor(originalInv);

             return new CompiledFunction(boundInvoker.type(), boundInvoker, bindConstructHandle(originalInv.getConstructor(), fn, args));

         }

         return new CompiledFunction(boundInvoker.type(), boundInvoker);

     }

     /**

      * Is this a ScriptFunction generated with strict semantics?

      * @return true if strict, false otherwise

      */

     public boolean isStrict() {

         return isStrict;

     }

     boolean isBuiltin() {

         return isBuiltin;

     }

     boolean isConstructor() {

         return isConstructor;

     }

     boolean needsCallee() {

         // we don't know if we need a callee or not unless we are generated

         ensureCodeGenerated();

         return code.needsCallee();

     }

     /**

      * Returns true if this is a non-strict, non-built-in function that requires non-primitive this argument

      * according to ECMA 10.4.3.

      * @return true if this argument must be an object

      */

     boolean needsWrappedThis() {

         return !isStrict && !isBuiltin;

     }

     String toSource() {

         return "function " + (name == null ? "" : name) + "() { [native code] }";

     }

     String getName() {

         return name;

     }

     /**

      * Get this function as a String containing its source code. If no source code

      * exists in this ScriptFunction, its contents will be displayed as {@code [native code]}

      *

      * @return string representation of this function

      */

     @Override

     public String toString() {

         final StringBuilder sb = new StringBuilder();

         sb.append("name='").

                 append(name.isEmpty() ? "<anonymous>" : name).

                 append("' ").

                 append(code.size()).

                 append(" invokers=").

                 append(code);

         return sb.toString();

     }

     /**

      * Pick the best invoker, i.e. the one version of this method with as narrow and specific

      * types as possible. If the call site arguments are objects, but boxed primitives we can

      * also try to get a primitive version of the method and do an unboxing filter, but then

      * we need to insert a guard that checks the argument is really always a boxed primitive

      * and not suddenly a "real" object

      *

      * @param callSiteType callsite type

      * @param args         arguments at callsite on first trampoline invocation

      * @return method handle to best invoker

      */

     MethodHandle getBestInvoker(final MethodType callSiteType, final Object[] args) {

         return getBest(callSiteType).getInvoker();

     }

     MethodHandle getBestInvoker(final MethodType callSiteType) {

         return getBestInvoker(callSiteType, null);

     }

     MethodHandle getBestConstructor(final MethodType callSiteType, final Object[] args) {

         if (!isConstructor()) {

             throw typeError("not.a.constructor", toSource());

         }

         ensureCodeGenerated();

         final CompiledFunction best = getBest(callSiteType);

         ensureConstructor(best);

         return best.getConstructor();

     }

     MethodHandle getBestConstructor(final MethodType callSiteType) {

         return getBestConstructor(callSiteType, null);

     }

     /**

      * Subclass responsibility. If we can have lazy code generation, this is a hook to ensure that

      * code exists before performing an operation.

      */

     protected void ensureCodeGenerated() {

         //empty

     }

     /**

      * Return a generic Object/Object invoker for this method. It will ensure code

      * is generated, get the most generic of all versions of this function and adapt it

      * to Objects.

      *

      * TODO this is only public because {@link JavaAdapterFactory} can't supply us with

      * a MethodType that we can use for lookup due to boostrapping problems. Can be fixed

      *

      * @return generic invoker of this script function

      */

     public final MethodHandle getGenericInvoker() {

         ensureCodeGenerated();

         return composeGenericMethod(code.mostGeneric().getInvoker());

     }

     final MethodHandle getGenericConstructor() {

         ensureCodeGenerated();

         ensureConstructor(code.mostGeneric());

         return composeGenericMethod(code.mostGeneric().getConstructor());

     }

     private CompiledFunction getBest(final MethodType callSiteType) {

         ensureCodeGenerated();

         return code.best(callSiteType);

     }

     /**

      * Allocates an object using this function's allocator.

      * @return the object allocated using this function's allocator, or null if the function doesn't have an allocator.

      */

     ScriptObject allocate() {

         return null;

     }

     /**

      * This method is used to create the immutable portion of a bound function.

      * See {@link ScriptFunction#makeBoundFunction(Object, Object[])}

      *

      * @param fn the original function being bound

      * @param self this reference to bind. Can be null.

      * @param args additional arguments to bind. Can be null.

      */

     ScriptFunctionData makeBoundFunctionData(final ScriptFunction fn, final Object self, final Object[] args) {

         ensureCodeGenerated();

         final Object[] allArgs = args == null ? ScriptRuntime.EMPTY_ARRAY : args;

         final int length = args == null ? 0 : args.length;

         CompiledFunctions boundList = new CompiledFunctions();

         for (final CompiledFunction inv : code) {

             boundList.add(bind(inv, fn, self, allArgs));

         }

         ScriptFunctionData boundData = new FinalScriptFunctionData(name, arity == -1 ? -1 : Math.max(0, arity - length), boundList, isStrict(), isBuiltin(), isConstructor());

         return boundData;

     }

     /**

      * Compose a constructor given a primordial constructor handle

      *

      * @param ctor         primordial constructor handle

      * @param needsCallee  do we need to pass a callee

      *

      * @return the composed constructor

      */

     protected MethodHandle composeConstructor(final MethodHandle ctor, final boolean needsCallee) {

         // If it was (callee, this, args...), permute it to (this, callee, args...). We're doing this because having

         // "this" in the first argument position is what allows the elegant folded composition of

         // (newFilter x constructor x allocator) further down below in the code. Also, ensure the composite constructor

         // always returns Object.

         MethodHandle composedCtor = needsCallee ? swapCalleeAndThis(ctor) : ctor;

         composedCtor = changeReturnTypeToObject(composedCtor);

         final MethodType ctorType = composedCtor.type();

         // Construct a dropping type list for NEWFILTER, but don't include constructor "this" into it, so it's actually

         // captured as "allocation" parameter of NEWFILTER after we fold the constructor into it.

         // (this, [callee, ]args...) => ([callee, ]args...)

         final Class<?>[] ctorArgs = ctorType.dropParameterTypes(0, 1).parameterArray();

         // Fold constructor into newFilter that replaces the return value from the constructor with the originally

         // allocated value when the originally allocated value is a primitive.

         // (result, this, [callee, ]args...) x (this, [callee, ]args...) => (this, [callee, ]args...)

         composedCtor = MH.foldArguments(MH.dropArguments(NEWFILTER, 2, ctorArgs), composedCtor);

         // allocate() takes a ScriptFunction and returns a newly allocated ScriptObject...

         if (needsCallee) {

             // ...we either fold it into the previous composition, if we need both the ScriptFunction callee object and

             // the newly allocated object in the arguments, so (this, callee, args...) x (callee) => (callee, args...),

             // or...

             return MH.foldArguments(composedCtor, ScriptFunction.ALLOCATE);

         }

         // ...replace the ScriptFunction argument with the newly allocated object, if it doesn't need the callee

         // (this, args...) filter (callee) => (callee, args...)

         return MH.filterArguments(composedCtor, 0, ScriptFunction.ALLOCATE);

     }

     /**

      * If this function's method handles need a callee parameter, swap the order of first two arguments for the passed

      * method handle. If this function's method handles don't need a callee parameter, returns the original method

      * handle unchanged.

      *

      * @param mh a method handle with order of arguments {@code (callee, this, args...)}

      *

      * @return a method handle with order of arguments {@code (this, callee, args...)}

      */

     private static MethodHandle swapCalleeAndThis(final MethodHandle mh) {

         final MethodType type = mh.type();

         assert type.parameterType(0) == ScriptFunction.class : type;

         assert type.parameterType(1) == Object.class : type;

         final MethodType newType = type.changeParameterType(0, Object.class).changeParameterType(1, ScriptFunction.class);

         final int[] reorder = new int[type.parameterCount()];

         reorder[0] = 1;

         assert reorder[1] == 0;

         for (int i = 2; i < reorder.length; ++i) {

             reorder[i] = i;

         }

         return MethodHandles.permuteArguments(mh, newType, reorder);

     }

     /**

      * Convert this argument for non-strict functions according to ES 10.4.3

      *

      * @param thiz the this argument

      *

      * @return the converted this object

      */

     private Object convertThisObject(final Object thiz) {

         if (!(thiz instanceof ScriptObject) && needsWrappedThis()) {

             if (JSType.nullOrUndefined(thiz)) {

                 return Context.getGlobalTrusted();

             }

             if (isPrimitiveThis(thiz)) {

                 return ((GlobalObject)Context.getGlobalTrusted()).wrapAsObject(thiz);

             }

         }

         return thiz;

     }

     static boolean isPrimitiveThis(final Object obj) {

         return obj instanceof String || obj instanceof ConsString ||

                obj instanceof Number || obj instanceof Boolean;

     }

     /**

      * Creates an invoker method handle for a bound function.

      *

      * @param targetFn the function being bound

      * @param originalInvoker an original invoker method handle for the function. This can be its generic invoker or

      * any of its specializations.

      * @param self the "this" value being bound

      * @param args additional arguments being bound

      *

      * @return a bound invoker method handle that will bind the self value and the specified arguments. The resulting

      * invoker never needs a callee; if the original invoker needed it, it will be bound to {@code fn}. The resulting

      * invoker still takes an initial {@code this} parameter, but it is always dropped and the bound {@code self} passed

      * to the original invoker on invocation.

      */

     private MethodHandle bindInvokeHandle(final MethodHandle originalInvoker, final ScriptFunction targetFn, final Object self, final Object[] args) {

         // Is the target already bound? If it is, we won't bother binding either callee or self as they're already bound

         // in the target and will be ignored anyway.

         final boolean isTargetBound = targetFn.isBoundFunction();

         final boolean needsCallee = needsCallee(originalInvoker);

         assert needsCallee == needsCallee() : "callee contract violation 2";

         assert !(isTargetBound && needsCallee); // already bound functions don't need a callee

         final Object boundSelf = isTargetBound ? null : convertThisObject(self);

         final MethodHandle boundInvoker;

         if (isVarArg(originalInvoker)) {

             // First, bind callee and this without arguments

             final MethodHandle noArgBoundInvoker;

             if (isTargetBound) {

                 // Don't bind either callee or this

                 noArgBoundInvoker = originalInvoker;

             } else if (needsCallee) {

                 // Bind callee and this

                 noArgBoundInvoker = MH.insertArguments(originalInvoker, 0, targetFn, boundSelf);

             } else {

                 // Only bind this

                 noArgBoundInvoker = MH.bindTo(originalInvoker, boundSelf);

             }

             // Now bind arguments

             if (args.length > 0) {

                 boundInvoker = varArgBinder(noArgBoundInvoker, args);

             } else {

                 boundInvoker = noArgBoundInvoker;

             }

         } else {

             // If target is already bound, insert additional bound arguments after "this" argument, at position 1.

             final int argInsertPos = isTargetBound ? 1 : 0;

             final Object[] boundArgs = new Object[Math.min(originalInvoker.type().parameterCount() - argInsertPos, args.length + (isTargetBound ? 0 : (needsCallee  ? 2 : 1)))];

             int next = 0;

             if (!isTargetBound) {

                 if (needsCallee) {

                     boundArgs[next++] = targetFn;

                 }

                 boundArgs[next++] = boundSelf;

             }

             // If more bound args were specified than the function can take, we'll just drop those.

             System.arraycopy(args, 0, boundArgs, next, boundArgs.length - next);

             // If target is already bound, insert additional bound arguments after "this" argument, at position 1;

             // "this" will get dropped anyway by the target invoker. We previously asserted that already bound functions

             // don't take a callee parameter, so we can know that the signature is (this[, args...]) therefore args

             // start at position 1. If the function is not bound, we start inserting arguments at position 0.

             boundInvoker = MH.insertArguments(originalInvoker, argInsertPos, boundArgs);

         }

         if (isTargetBound) {

             return boundInvoker;

         }

         // If the target is not already bound, add a dropArguments that'll throw away the passed this

         return MH.dropArguments(boundInvoker, 0, Object.class);

     }

     /**

      * Creates a constructor method handle for a bound function using the passed constructor handle.

      *

      * @param originalConstructor the constructor handle to bind. It must be a composed constructor.

      * @param fn the function being bound

      * @param args arguments being bound

      *

      * @return a bound constructor method handle that will bind the specified arguments. The resulting constructor never

      * needs a callee; if the original constructor needed it, it will be bound to {@code fn}. The resulting constructor

      * still takes an initial {@code this} parameter and passes it to the underlying original constructor. Finally, if

      * this script function data object has no constructor handle, null is returned.

      */

     private static MethodHandle bindConstructHandle(final MethodHandle originalConstructor, final ScriptFunction fn, final Object[] args) {

         assert originalConstructor != null;

         // If target function is already bound, don't bother binding the callee.

         final MethodHandle calleeBoundConstructor = fn.isBoundFunction() ? originalConstructor :

             MH.dropArguments(MH.bindTo(originalConstructor, fn), 0, ScriptFunction.class);

         if (args.length == 0) {

             return calleeBoundConstructor;

         }

         if (isVarArg(calleeBoundConstructor)) {

             return varArgBinder(calleeBoundConstructor, args);

         }

         final Object[] boundArgs;

         final int maxArgCount = calleeBoundConstructor.type().parameterCount() - 1;

         if (args.length <= maxArgCount) {

             boundArgs = args;

         } else {

             boundArgs = new Object[maxArgCount];

             System.arraycopy(args, 0, boundArgs, 0, maxArgCount);

         }

         return MH.insertArguments(calleeBoundConstructor, 1, boundArgs);

     }

     /**

      * Takes a method handle, and returns a potentially different method handle that can be used in

      * {@code ScriptFunction#invoke(Object, Object...)} or {code ScriptFunction#construct(Object, Object...)}.

      * The returned method handle will be sure to return {@code Object}, and will have all its parameters turned into

      * {@code Object} as well, except for the following ones:

      * <ul>

      *   <li>a last parameter of type {@code Object[]} which is used for vararg functions,</li>

      *   <li>the first argument, which is forced to be {@link ScriptFunction}, in case the function receives itself

      *   (callee) as an argument.</li>

      * </ul>

      *

      * @param mh the original method handle

      *

      * @return the new handle, conforming to the rules above.

      */

     protected MethodHandle composeGenericMethod(final MethodHandle mh) {

         final MethodType type = mh.type();

         MethodType newType = type.generic();

         if (isVarArg(mh)) {

             newType = newType.changeParameterType(type.parameterCount() - 1, Object[].class);

         }

         if (needsCallee(mh)) {

             newType = newType.changeParameterType(0, ScriptFunction.class);

         }

         return type.equals(newType) ? mh : mh.asType(newType);

     }

     /**

      * Execute this script function.

      *

      * @param self  Target object.

      * @param arguments  Call arguments.

      * @return ScriptFunction result.

      *

      * @throws Throwable if there is an exception/error with the invocation or thrown from it

      */

     Object invoke(final ScriptFunction fn, final Object self, final Object... arguments) throws Throwable {

         final MethodHandle mh = getGenericInvoker();

         final Object       selfObj    = convertThisObject(self);

         final Object[]     args       = arguments == null ? ScriptRuntime.EMPTY_ARRAY : arguments;

         if (isVarArg(mh)) {

             if (needsCallee(mh)) {

                 return mh.invokeExact(fn, selfObj, args);

             }

             return mh.invokeExact(selfObj, args);

         }

         final int paramCount = mh.type().parameterCount();

         if (needsCallee(mh)) {

             switch (paramCount) {

             case 2:

                 return mh.invokeExact(fn, selfObj);

             case 3:

                 return mh.invokeExact(fn, selfObj, getArg(args, 0));

             case 4:

                 return mh.invokeExact(fn, selfObj, getArg(args, 0), getArg(args, 1));

             case 5:

                 return mh.invokeExact(fn, selfObj, getArg(args, 0), getArg(args, 1), getArg(args, 2));

             default:

                 return mh.invokeWithArguments(withArguments(fn, selfObj, paramCount, args));

             }

         }

         switch (paramCount) {

         case 1:

             return mh.invokeExact(selfObj);

         case 2:

             return mh.invokeExact(selfObj, getArg(args, 0));

         case 3:

             return mh.invokeExact(selfObj, getArg(args, 0), getArg(args, 1));

         case 4:

             return mh.invokeExact(selfObj, getArg(args, 0), getArg(args, 1), getArg(args, 2));

         default:

             return mh.invokeWithArguments(withArguments(null, selfObj, paramCount, args));

         }

     }

     Object construct(final ScriptFunction fn, final Object... arguments) throws Throwable {

         final MethodHandle mh = getGenericConstructor();

         final Object[]     args       = arguments == null ? ScriptRuntime.EMPTY_ARRAY : arguments;

         if (isVarArg(mh)) {

             if (needsCallee(mh)) {

                 return mh.invokeExact(fn, args);

             }

             return mh.invokeExact(args);

         }

         final int paramCount = mh.type().parameterCount();

         if (needsCallee(mh)) {

             switch (paramCount) {

             case 1:

                 return mh.invokeExact(fn);

             case 2:

                 return mh.invokeExact(fn, getArg(args, 0));

             case 3:

                 return mh.invokeExact(fn, getArg(args, 0), getArg(args, 1));

             case 4:

                 return mh.invokeExact(fn, getArg(args, 0), getArg(args, 1), getArg(args, 2));

             default:

                 return mh.invokeWithArguments(withArguments(fn, paramCount, args));

             }

         }

         switch (paramCount) {

         case 0:

             return mh.invokeExact();

         case 1:

             return mh.invokeExact(getArg(args, 0));

         case 2:

             return mh.invokeExact(getArg(args, 0), getArg(args, 1));

         case 3:

             return mh.invokeExact(getArg(args, 0), getArg(args, 1), getArg(args, 2));

         default:

             return mh.invokeWithArguments(withArguments(null, paramCount, args));

         }

     }

     private static Object getArg(final Object[] args, final int i) {

         return i < args.length ? args[i] : UNDEFINED;

     }

     private static Object[] withArguments(final ScriptFunction fn, final int argCount, final Object[] args) {

         final Object[] finalArgs = new Object[argCount];

         int nextArg = 0;

         if (fn != null) {

             //needs callee

             finalArgs[nextArg++] = fn;

         }

         // Don't add more args that there is argCount in the handle (including self and callee).

         for (int i = 0; i < args.length && nextArg < argCount;) {

             finalArgs[nextArg++] = args[i++];

         }

         // If we have fewer args than argCount, pad with undefined.

         while (nextArg < argCount) {

             finalArgs[nextArg++] = UNDEFINED;

         }

         return finalArgs;

     }

     private static Object[] withArguments(final ScriptFunction fn, final Object self, final int argCount, final Object[] args) {

         final Object[] finalArgs = new Object[argCount];

         int nextArg = 0;

         if (fn != null) {

             //needs callee

             finalArgs[nextArg++] = fn;

         }

         finalArgs[nextArg++] = self;

         // Don't add more args that there is argCount in the handle (including self and callee).

         for (int i = 0; i < args.length && nextArg < argCount;) {

             finalArgs[nextArg++] = args[i++];

         }

         // If we have fewer args than argCount, pad with undefined.

         while (nextArg < argCount) {

             finalArgs[nextArg++] = UNDEFINED;

         }

         return finalArgs;

     }

     /**

      * Takes a variable-arity method and binds a variable number of arguments in it. The returned method will filter the

      * vararg array and pass a different array that prepends the bound arguments in front of the arguments passed on

      * invocation

      *

      * @param mh the handle

      * @param args the bound arguments

      *

      * @return the bound method handle

      */

     private static MethodHandle varArgBinder(final MethodHandle mh, final Object[] args) {

         assert args != null;

         assert args.length > 0;

         return MH.filterArguments(mh, mh.type().parameterCount() - 1, MH.bindTo(BIND_VAR_ARGS, args));

     }

     /**

      * Adapts the method handle so its return type is {@code Object}. If the handle's return type is already

      * {@code Object}, the handle is returned unchanged.

      *

      * @param mh the handle to adapt

      * @return the adapted handle

      */

     private static MethodHandle changeReturnTypeToObject(final MethodHandle mh) {

         return MH.asType(mh, mh.type().changeReturnType(Object.class));

     }

     private void ensureConstructor(final CompiledFunction inv) {

         if (!inv.hasConstructor()) {

             inv.setConstructor(composeConstructor(inv.getInvoker(), needsCallee(inv.getInvoker())));

         }

     }

     /**

      * Heuristic to figure out if the method handle has a callee argument. If it's type is either

      * {@code (boolean, Object, ScriptFunction, ...)} or {@code (Object, ScriptFunction, ...)}, then we'll assume it has

      * a callee argument. We need this as the constructor above is not passed this information, and can't just blindly

      * assume it's false (notably, it's being invoked for creation of new scripts, and scripts have scopes, therefore

      * they also always receive a callee).

      *

      * @param mh the examined method handle

      *

      * @return true if the method handle expects a callee, false otherwise

      */

     protected static boolean needsCallee(final MethodHandle mh) {

         final MethodType type   = mh.type();

         final int        length = type.parameterCount();

         if (length == 0) {

             return false;

         }

         if (type.parameterType(0) == boolean.class) {

             return length > 1 && type.parameterType(1) == ScriptFunction.class;

         }

         return type.parameterType(0) == ScriptFunction.class;

     }

     /**

      * Check if a javascript function methodhandle is a vararg handle

      *

      * @param mh method handle to check

      *

      * @return true if vararg

      */

     protected static boolean isVarArg(final MethodHandle mh) {

         final MethodType type = mh.type();

         return type.parameterType(type.parameterCount() - 1).isArray();

     }

     @SuppressWarnings("unused")

     private static Object[] bindVarArgs(final Object[] array1, final Object[] array2) {

         if (array2 == null) {

             // Must clone it, as we can't allow the receiving method to alter the array

             return array1.clone();

         }

         final int l2 = array2.length;

         if (l2 == 0) {

             return array1.clone();

         }

         final int l1 = array1.length;

         final Object[] concat = new Object[l1 + l2];

         System.arraycopy(array1, 0, concat, 0, l1);

         System.arraycopy(array2, 0, concat, l1, l2);

         return concat;

     }

     @SuppressWarnings("unused")

     private static Object newFilter(final Object result, final Object allocation) {

         return (result instanceof ScriptObject || !JSType.isPrimitive(result))? result : allocation;

     }

     private static MethodHandle findOwnMH(final String name, final Class<?> rtype, final Class<?>... types) {

         return MH.findStatic(MethodHandles.lookup(), ScriptFunctionData.class, name, MH.type(rtype, types));

     }

 }