dynalink/beans/SingleDynamicMethod.java

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/*
 * This file is available under and governed by the GNU General Public
 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file, and Oracle licenses the original version of this file under the BSD
 * license:
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/*
   Copyright 2009-2013 Attila Szegedi

   Licensed under both the Apache License, Version 2.0 (the "Apache License")
   and the BSD License (the "BSD License"), with licensee being free to
   choose either of the two at their discretion.

   You may not use this file except in compliance with either the Apache
   License or the BSD License.

   If you choose to use this file in compliance with the Apache License, the
   following notice applies to you:

       You may obtain a copy of the Apache License at

           http://www.apache.org/licenses/LICENSE-2.0

       Unless required by applicable law or agreed to in writing, software
       distributed under the License is distributed on an "AS IS" BASIS,
       WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
       implied. See the License for the specific language governing
       permissions and limitations under the License.

   If you choose to use this file in compliance with the BSD License, the
   following notice applies to you:

       Redistribution and use in source and binary forms, with or without
       modification, are permitted provided that the following conditions are
       met:
       * Redistributions of source code must retain the above copyright
         notice, this list of conditions and the following disclaimer.
       * Redistributions in binary form must reproduce the above copyright
         notice, this list of conditions and the following disclaimer in the
         documentation and/or other materials provided with the distribution.
       * Neither the name of the copyright holder nor the names of
         contributors may be used to endorse or promote products derived from
         this software without specific prior written permission.

       THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
       IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
       TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
       PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL COPYRIGHT HOLDER
       BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
       CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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       ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

package jdk.dynalink.beans;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.lang.reflect.Array;
import java.util.StringTokenizer;
import jdk.dynalink.CallSiteDescriptor;
import jdk.dynalink.linker.LinkerServices;
import jdk.dynalink.linker.support.Guards;
import jdk.dynalink.linker.support.Lookup;

/**
 * Base class for dynamic methods that dispatch to a single target Java method or constructor. Handles adaptation of the
 * target method to a call site type (including mapping variable arity methods to a call site signature with different
 * arity).
 */
abstract class SingleDynamicMethod extends DynamicMethod {

    private static final MethodHandle CAN_CONVERT_TO = Lookup.findOwnStatic(MethodHandles.lookup(), "canConvertTo", boolean.class, LinkerServices.class, Class.class, Object.class);

    SingleDynamicMethod(final String name) {
        super(name);
    }

    /**
     * Returns true if this method is variable arity.
     * @return true if this method is variable arity.
     */
    abstract boolean isVarArgs();

    /**
     * Returns this method's native type.
     * @return this method's native type.
     */
    abstract MethodType getMethodType();

    /**
     * Given a specified call site descriptor, returns a method handle to this method's target. The target
     * should only depend on the descriptor's lookup, and it should only retrieve it (as a privileged
     * operation) when it is absolutely needed.
     * @param desc the call site descriptor to use.
     * @return the handle to this method's target method.
     */
    abstract MethodHandle getTarget(CallSiteDescriptor desc);

    @Override
    MethodHandle getInvocation(final CallSiteDescriptor callSiteDescriptor, final LinkerServices linkerServices) {
        return getInvocation(getTarget(callSiteDescriptor), callSiteDescriptor.getMethodType(),
                linkerServices);
    }

    @Override
    SingleDynamicMethod getMethodForExactParamTypes(final String paramTypes) {
        return typeMatchesDescription(paramTypes, getMethodType()) ? this : null;
    }

    @Override
    boolean contains(final SingleDynamicMethod method) {
        return getMethodType().parameterList().equals(method.getMethodType().parameterList());
    }

    static String getMethodNameWithSignature(final MethodType type, final String methodName, final boolean withReturnType) {
        final String typeStr = type.toString();
        final int retTypeIndex = typeStr.lastIndexOf(')') + 1;
        int secondParamIndex = typeStr.indexOf(',') + 1;
        if(secondParamIndex == 0) {
            secondParamIndex = retTypeIndex - 1;
        }
        final StringBuilder b = new StringBuilder();
        if (withReturnType) {
            b.append(typeStr, retTypeIndex, typeStr.length()).append(' ');
        }
        return b.append(methodName).append('(').append(typeStr, secondParamIndex, retTypeIndex).toString();
    }

    /**
     * Given a method handle and a call site type, adapts the method handle to the call site type. Performs type
     * conversions as needed using the specified linker services, and in case that the method handle is a vararg
     * collector, matches it to the arity of the call site. The type of the return value is only changed if it can be
     * converted using a conversion that loses neither precision nor magnitude, see
     * {@link LinkerServices#asTypeLosslessReturn(MethodHandle, MethodType)}.
     * @param target the method handle to adapt
     * @param callSiteType the type of the call site
     * @param linkerServices the linker services used for type conversions
     * @return the adapted method handle.
     */
    static MethodHandle getInvocation(final MethodHandle target, final MethodType callSiteType, final LinkerServices linkerServices) {
        final MethodHandle filteredTarget = linkerServices.filterInternalObjects(target);
        final MethodType methodType = filteredTarget.type();
        final int paramsLen = methodType.parameterCount();
        final boolean varArgs = target.isVarargsCollector();
        final MethodHandle fixTarget = varArgs ? filteredTarget.asFixedArity() : filteredTarget;
        final int fixParamsLen = varArgs ? paramsLen - 1 : paramsLen;
        final int argsLen = callSiteType.parameterCount();
        if(argsLen < fixParamsLen) {
            // Less actual arguments than number of fixed declared arguments; can't invoke.
            return null;
        }
        // Method handle has the same number of fixed arguments as the call site type
        if(argsLen == fixParamsLen) {
            // Method handle that matches the number of actual arguments as the number of fixed arguments
            final MethodHandle matchedMethod;
            if(varArgs) {
                // If vararg, add a zero-length array of the expected type as the last argument to signify no variable
                // arguments.
                matchedMethod = MethodHandles.insertArguments(fixTarget, fixParamsLen, Array.newInstance(
                        methodType.parameterType(fixParamsLen).getComponentType(), 0));
            } else {
                // Otherwise, just use the method
                matchedMethod = fixTarget;
            }
            return createConvertingInvocation(matchedMethod, linkerServices, callSiteType);
        }

        // What's below only works for varargs
        if(!varArgs) {
            return null;
        }

        final Class<?> varArgType = methodType.parameterType(fixParamsLen);
        // Handle a somewhat sinister corner case: caller passes exactly one argument in the vararg position, and we
        // must handle both a prepacked vararg array as well as a genuine 1-long vararg sequence.
        if(argsLen == paramsLen) {
            final Class<?> callSiteLastArgType = callSiteType.parameterType(fixParamsLen);
            if(varArgType.isAssignableFrom(callSiteLastArgType)) {
                // Call site signature guarantees we'll always be passed a single compatible array; just link directly
                // to the method, introducing necessary conversions. Also, preserve it being a variable arity method.
                return createConvertingInvocation(filteredTarget, linkerServices, callSiteType).asVarargsCollector(
                        callSiteLastArgType);
            }

            // This method handle takes the single argument and packs it into a newly allocated single-element array. It
            // will be used when the incoming argument can't be converted to the vararg array type (the "vararg packer"
            // method).
            final MethodHandle varArgCollectingInvocation = createConvertingInvocation(collectArguments(fixTarget,
                    argsLen), linkerServices, callSiteType);

            // Is call site type assignable from an array type (e.g. Object:int[], or Object[]:String[])
            final boolean isAssignableFromArray = callSiteLastArgType.isAssignableFrom(varArgType);
            // Do we have a custom conversion that can potentially convert the call site type to an array?
            final boolean isCustomConvertible = linkerServices.canConvert(callSiteLastArgType, varArgType);
            if(!isAssignableFromArray && !isCustomConvertible) {
                // Call site signature guarantees the argument can definitely not be converted to an array (i.e. it is
                // primitive), and no conversion can help with it either. Link immediately to a vararg-packing method
                // handle.
                return varArgCollectingInvocation;
            }

            // This method handle employs language-specific conversions to convert the last argument into an array of
            // vararg type.
            final MethodHandle arrayConvertingInvocation = createConvertingInvocation(MethodHandles.filterArguments(
                    fixTarget, fixParamsLen, linkerServices.getTypeConverter(callSiteLastArgType, varArgType)),
                    linkerServices, callSiteType);

            // This method handle determines whether the value can be converted to the array of vararg type using a
            // language-specific conversion.
            final MethodHandle canConvertArgToArray = MethodHandles.insertArguments(CAN_CONVERT_TO, 0, linkerServices,
                    varArgType);

            // This one adjusts the previous one for the location of the argument and the call site type.
            final MethodHandle canConvertLastArgToArray = MethodHandles.dropArguments(canConvertArgToArray, 0,
                    MethodType.genericMethodType(fixParamsLen).parameterList()).asType(callSiteType.changeReturnType(boolean.class));

            // This one takes the previous ones and combines them into a method handle that converts the argument into
            // a vararg array when it can, otherwise falls back to the vararg packer.
            final MethodHandle convertToArrayWhenPossible = MethodHandles.guardWithTest(canConvertLastArgToArray,
                    arrayConvertingInvocation, varArgCollectingInvocation);

            if(isAssignableFromArray) {
                return MethodHandles.guardWithTest(
                        // Is incoming parameter already a compatible array?
                        Guards.isInstance(varArgType, fixParamsLen, callSiteType),
                        // Yes: just pass it to the method
                        createConvertingInvocation(fixTarget, linkerServices, callSiteType),
                        // No: either go through a custom conversion, or if it is not possible, go directly to the
                        // vararg packer.
                        isCustomConvertible ? convertToArrayWhenPossible : varArgCollectingInvocation);
            }

            // Just do the custom conversion with fallback to the vararg packer logic.
            assert isCustomConvertible;
            return convertToArrayWhenPossible;
        }

        // Remaining case: more than one vararg.
        return createConvertingInvocation(collectArguments(fixTarget, argsLen), linkerServices, callSiteType);
    }

    @SuppressWarnings("unused")
    private static boolean canConvertTo(final LinkerServices linkerServices, final Class<?> to, final Object obj) {
        return obj == null ? false : linkerServices.canConvert(obj.getClass(), to);
    }

    /**
     * Creates a method handle out of the original target that will collect the varargs for the exact component type of
     * the varArg array. Note that this will nicely trigger language-specific type converters for exactly those varargs
     * for which it is necessary when later passed to linkerServices.convertArguments().
     *
     * @param target the original method handle
     * @param parameterCount the total number of arguments in the new method handle
     * @return a collecting method handle
     */
    static MethodHandle collectArguments(final MethodHandle target, final int parameterCount) {
        final MethodType methodType = target.type();
        final int fixParamsLen = methodType.parameterCount() - 1;
        final Class<?> arrayType = methodType.parameterType(fixParamsLen);
        return target.asCollector(arrayType, parameterCount - fixParamsLen);
    }

    private static MethodHandle createConvertingInvocation(final MethodHandle sizedMethod,
            final LinkerServices linkerServices, final MethodType callSiteType) {
        return linkerServices.asTypeLosslessReturn(sizedMethod, callSiteType);
    }

    private static boolean typeMatchesDescription(final String paramTypes, final MethodType type) {
        final StringTokenizer tok = new StringTokenizer(paramTypes, ", ");
        for(int i = 1; i < type.parameterCount(); ++i) { // i = 1 as we ignore the receiver
            if(!(tok.hasMoreTokens() && typeNameMatches(tok.nextToken(), type.parameterType(i)))) {
                return false;
            }
        }
        return !tok.hasMoreTokens();
    }

    private static boolean typeNameMatches(final String typeName, final Class<?> type) {
        return  typeName.equals(typeName.indexOf('.') == -1 ? type.getSimpleName() : type.getCanonicalName());
    }
}