MaximallySpecific.java

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 * This file is available under and governed by the GNU General Public
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 * However, the following notice accompanied the original version of this
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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.
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         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
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package jdk.internal.dynalink.beans;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodType;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import jdk.internal.dynalink.linker.ConversionComparator.Comparison;
import jdk.internal.dynalink.linker.LinkerServices;
import jdk.internal.dynalink.support.TypeUtilities;

/**
 * Utility class that encapsulates the algorithm for choosing the maximally specific methods.
 *
 * @author Attila Szegedi
 */
class MaximallySpecific {
    /**
     * Given a list of methods, returns a list of maximally specific methods.
     *
     * @param methods the list of methods
     * @param varArgs whether to assume the methods are varargs
     * @return the list of maximally specific methods.
     */
    static List<SingleDynamicMethod> getMaximallySpecificMethods(final List<SingleDynamicMethod> methods, final boolean varArgs) {
        return getMaximallySpecificSingleDynamicMethods(methods, varArgs, null, null);
    }

    private abstract static class MethodTypeGetter<T> {
        abstract MethodType getMethodType(T t);
    }

    private static final MethodTypeGetter<MethodHandle> METHOD_HANDLE_TYPE_GETTER =
            new MethodTypeGetter<MethodHandle>() {
        @Override
        MethodType getMethodType(final MethodHandle t) {
            return t.type();
        }
    };

    private static final MethodTypeGetter<SingleDynamicMethod> DYNAMIC_METHOD_TYPE_GETTER =
            new MethodTypeGetter<SingleDynamicMethod>() {
        @Override
        MethodType getMethodType(final SingleDynamicMethod t) {
            return t.getMethodType();
        }
    };

     /**
      * Given a list of methods handles, returns a list of maximally specific methods, applying language-runtime
      * specific conversion preferences.
      *
      * @param methods the list of method handles
      * @param varArgs whether to assume the method handles are varargs
      * @param argTypes concrete argument types for the invocation
      * @return the list of maximally specific method handles.
      */
     static List<MethodHandle> getMaximallySpecificMethodHandles(final List<MethodHandle> methods, final boolean varArgs,
             final Class<?>[] argTypes, final LinkerServices ls) {
         return getMaximallySpecificMethods(methods, varArgs, argTypes, ls, METHOD_HANDLE_TYPE_GETTER);
     }

     /**
      * Given a list of methods, returns a list of maximally specific methods, applying language-runtime specific
      * conversion preferences.
      *
      * @param methods the list of methods
      * @param varArgs whether to assume the methods are varargs
      * @param argTypes concrete argument types for the invocation
      * @return the list of maximally specific methods.
      */
     static List<SingleDynamicMethod> getMaximallySpecificSingleDynamicMethods(final List<SingleDynamicMethod> methods,
             final boolean varArgs, final Class<?>[] argTypes, final LinkerServices ls) {
         return getMaximallySpecificMethods(methods, varArgs, argTypes, ls, DYNAMIC_METHOD_TYPE_GETTER);
     }

    /**
     * Given a list of methods, returns a list of maximally specific methods, applying language-runtime specific
     * conversion preferences.
     *
     * @param methods the list of methods
     * @param varArgs whether to assume the methods are varargs
     * @param argTypes concrete argument types for the invocation
     * @return the list of maximally specific methods.
     */
    private static <T> List<T> getMaximallySpecificMethods(final List<T> methods, final boolean varArgs,
            final Class<?>[] argTypes, final LinkerServices ls, final MethodTypeGetter<T> methodTypeGetter) {
        if(methods.size() < 2) {
            return methods;
        }
        final LinkedList<T> maximals = new LinkedList<>();
        for(final T m: methods) {
            final MethodType methodType = methodTypeGetter.getMethodType(m);
            boolean lessSpecific = false;
            for(final Iterator<T> maximal = maximals.iterator(); maximal.hasNext();) {
                final T max = maximal.next();
                switch(isMoreSpecific(methodType, methodTypeGetter.getMethodType(max), varArgs, argTypes, ls)) {
                    case TYPE_1_BETTER: {
                        maximal.remove();
                        break;
                    }
                    case TYPE_2_BETTER: {
                        lessSpecific = true;
                        break;
                    }
                    case INDETERMINATE: {
                        // do nothing
                        break;
                    }
                    default: {
                        throw new AssertionError();
                    }
                }
            }
            if(!lessSpecific) {
                maximals.addLast(m);
            }
        }
        return maximals;
    }

    private static Comparison isMoreSpecific(final MethodType t1, final MethodType t2, final boolean varArgs, final Class<?>[] argTypes,
            final LinkerServices ls) {
        final int pc1 = t1.parameterCount();
        final int pc2 = t2.parameterCount();
        assert varArgs || (pc1 == pc2) && (argTypes == null || argTypes.length == pc1);
        assert (argTypes == null) == (ls == null);
        final int maxPc = Math.max(Math.max(pc1, pc2), argTypes == null ? 0 : argTypes.length);
        boolean t1MoreSpecific = false;
        boolean t2MoreSpecific = false;
        // NOTE: Starting from 1 as overloaded method resolution doesn't depend on 0th element, which is the type of
        // 'this'. We're only dealing with instance methods here, not static methods. Actually, static methods will have
        // a fake 'this' of type StaticClass.
        for(int i = 1; i < maxPc; ++i) {
            final Class<?> c1 = getParameterClass(t1, pc1, i, varArgs);
            final Class<?> c2 = getParameterClass(t2, pc2, i, varArgs);
            if(c1 != c2) {
                final Comparison cmp = compare(c1, c2, argTypes, i, ls);
                if(cmp == Comparison.TYPE_1_BETTER && !t1MoreSpecific) {
                    t1MoreSpecific = true;
                    if(t2MoreSpecific) {
                        return Comparison.INDETERMINATE;
                    }
                }
                if(cmp == Comparison.TYPE_2_BETTER && !t2MoreSpecific) {
                    t2MoreSpecific = true;
                    if(t1MoreSpecific) {
                        return Comparison.INDETERMINATE;
                    }
                }
            }
        }
        if(t1MoreSpecific) {
            return Comparison.TYPE_1_BETTER;
        } else if(t2MoreSpecific) {
            return Comparison.TYPE_2_BETTER;
        }
        return Comparison.INDETERMINATE;
    }

    private static Comparison compare(final Class<?> c1, final Class<?> c2, final Class<?>[] argTypes, final int i, final LinkerServices cmp) {
        if(cmp != null) {
            final Comparison c = cmp.compareConversion(argTypes[i], c1, c2);
            if(c != Comparison.INDETERMINATE) {
                return c;
            }
        }
        if(TypeUtilities.isSubtype(c1, c2)) {
            return Comparison.TYPE_1_BETTER;
        } if(TypeUtilities.isSubtype(c2, c1)) {
            return Comparison.TYPE_2_BETTER;
        }
        return Comparison.INDETERMINATE;
    }

    private static Class<?> getParameterClass(final MethodType t, final int l, final int i, final boolean varArgs) {
        return varArgs && i >= l - 1 ? t.parameterType(l - 1).getComponentType() : t.parameterType(i);
    }
}