jdk/dynalink/TypeConverterFactory.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.
       * Redistributions in binary form must reproduce the above copyright
         notice, this list of conditions and the following disclaimer in the
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       * Neither the name of the copyright holder nor the names of
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         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.dynalink;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodHandles.Lookup;
import java.lang.invoke.MethodType;
import java.lang.invoke.WrongMethodTypeException;
import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.LinkedList;
import java.util.List;
import java.util.function.Supplier;
import jdk.dynalink.internal.AccessControlContextFactory;
import jdk.dynalink.linker.ConversionComparator;
import jdk.dynalink.linker.ConversionComparator.Comparison;
import jdk.dynalink.linker.GuardedInvocation;
import jdk.dynalink.linker.GuardingTypeConverterFactory;
import jdk.dynalink.linker.LinkerServices;
import jdk.dynalink.linker.MethodTypeConversionStrategy;
import jdk.dynalink.linker.support.TypeUtilities;

/**
 * A factory for type converters. This class is the main implementation behind the
 * {@link LinkerServices#asType(MethodHandle, MethodType)}. It manages the known {@link GuardingTypeConverterFactory}
 * instances and creates appropriate converters for method handles.
 */
final class TypeConverterFactory {
    private static final AccessControlContext GET_CLASS_LOADER_CONTEXT =
            AccessControlContextFactory.createAccessControlContext("getClassLoader");

    private final GuardingTypeConverterFactory[] factories;
    private final ConversionComparator[] comparators;
    private final MethodTypeConversionStrategy autoConversionStrategy;

    private final ClassValue<ClassMap<MethodHandle>> converterMap = new ClassValue<ClassMap<MethodHandle>>() {
        @Override
        protected ClassMap<MethodHandle> computeValue(final Class<?> sourceType) {
            return new ClassMap<MethodHandle>(getClassLoader(sourceType)) {
                @Override
                protected MethodHandle computeValue(final Class<?> targetType) {
                    try {
                        return createConverter(sourceType, targetType);
                    } catch (final RuntimeException e) {
                        throw e;
                    } catch (final Exception e) {
                        throw new RuntimeException(e);
                    }
                }
            };
        }
    };

    private final ClassValue<ClassMap<MethodHandle>> converterIdentityMap = new ClassValue<ClassMap<MethodHandle>>() {
        @Override
        protected ClassMap<MethodHandle> computeValue(final Class<?> sourceType) {
            return new ClassMap<MethodHandle>(getClassLoader(sourceType)) {
                @Override
                protected MethodHandle computeValue(final Class<?> targetType) {
                    if(!canAutoConvert(sourceType, targetType)) {
                        final MethodHandle converter = getCacheableTypeConverter(sourceType, targetType);
                        if(converter != IDENTITY_CONVERSION) {
                            return converter;
                        }
                    }
                    return IDENTITY_CONVERSION.asType(MethodType.methodType(targetType, sourceType));
                }
            };
        }
    };

    private final ClassValue<ClassMap<Boolean>> canConvert = new ClassValue<ClassMap<Boolean>>() {
        @Override
        protected ClassMap<Boolean> computeValue(final Class<?> sourceType) {
            return new ClassMap<Boolean>(getClassLoader(sourceType)) {
                @Override
                protected Boolean computeValue(final Class<?> targetType) {
                    try {
                        return getTypeConverterNull(sourceType, targetType) != null;
                    } catch (final RuntimeException e) {
                        throw e;
                    } catch (final Exception e) {
                        throw new RuntimeException(e);
                    }
                }
            };
        }
    };

    private static ClassLoader getClassLoader(final Class<?> clazz) {
        return AccessController.doPrivileged(new PrivilegedAction<ClassLoader>() {
            @Override
            public ClassLoader run() {
                return clazz.getClassLoader();
            }
        }, GET_CLASS_LOADER_CONTEXT);
    }

    /**
     * Creates a new type converter factory from the available {@link GuardingTypeConverterFactory} instances.
     *
     * @param factories the {@link GuardingTypeConverterFactory} instances to compose.
     * @param autoConversionStrategy conversion strategy for automatic type conversions. After
     * {@link #asType(java.lang.invoke.MethodHandle, java.lang.invoke.MethodType)} has applied all custom
     * conversions to a method handle, it still needs to effect
     * {@link TypeUtilities#isMethodInvocationConvertible(Class, Class) method invocation conversions} that
     * can usually be automatically applied as per
     * {@link java.lang.invoke.MethodHandle#asType(java.lang.invoke.MethodType)}.
     * However, sometimes language runtimes will want to customize even those conversions for their own call
     * sites. A typical example is allowing unboxing of null return values, which is by default prohibited by
     * ordinary {@code MethodHandles.asType}. In this case, a language runtime can install its own custom
     * automatic conversion strategy, that can deal with null values. Note that when the strategy's
     * {@link MethodTypeConversionStrategy#asType(java.lang.invoke.MethodHandle, java.lang.invoke.MethodType)}
     * is invoked, the custom language conversions will already have been applied to the method handle, so by
     * design the difference between the handle's current method type and the desired final type will always
     * only be ones that can be subjected to method invocation conversions. Can be null, in which case no
     * custom strategy is employed.
     */
    TypeConverterFactory(final Iterable<? extends GuardingTypeConverterFactory> factories,
            final MethodTypeConversionStrategy autoConversionStrategy) {
        final List<GuardingTypeConverterFactory> l = new LinkedList<>();
        final List<ConversionComparator> c = new LinkedList<>();
        for(final GuardingTypeConverterFactory factory: factories) {
            l.add(factory);
            if(factory instanceof ConversionComparator) {
                c.add((ConversionComparator)factory);
            }
        }
        this.factories = l.toArray(new GuardingTypeConverterFactory[0]);
        this.comparators = c.toArray(new ConversionComparator[0]);
        this.autoConversionStrategy = autoConversionStrategy;
    }

    /**
     * Similar to {@link MethodHandle#asType(MethodType)} except it also hooks in method handles produced by
     * {@link GuardingTypeConverterFactory} implementations, providing for language-specific type coercing of
     * parameters. For all conversions that are not a JLS method invocation conversion it'll insert
     * {@link MethodHandles#filterArguments(MethodHandle, int, MethodHandle...)} with composite filters
     * provided by {@link GuardingTypeConverterFactory} implementations. For the remaining JLS method invocation
     * conversions, it will invoke {@link MethodTypeConversionStrategy#asType(MethodHandle, MethodType)} first
     * if an automatic conversion strategy was specified in the
     * {@link #TypeConverterFactory(Iterable, MethodTypeConversionStrategy) constructor}, and finally apply
     * {@link MethodHandle#asType(MethodType)} for any remaining conversions.
     *
     * @param handle target method handle
     * @param fromType the types of source arguments
     * @return a method handle that is a suitable combination of {@link MethodHandle#asType(MethodType)},
     * {@link MethodTypeConversionStrategy#asType(MethodHandle, MethodType)}, and
     * {@link MethodHandles#filterArguments(MethodHandle, int, MethodHandle...)} with
     * {@link GuardingTypeConverterFactory} produced type converters as filters.
     */
    MethodHandle asType(final MethodHandle handle, final MethodType fromType) {
        MethodHandle newHandle = handle;
        final MethodType toType = newHandle.type();
        final int l = toType.parameterCount();
        if(l != fromType.parameterCount()) {
            throw new WrongMethodTypeException("Parameter counts differ: " + handle.type() + " vs. " + fromType);
        }
        int pos = 0;
        final List<MethodHandle> converters = new LinkedList<>();
        for(int i = 0; i < l; ++i) {
            final Class<?> fromParamType = fromType.parameterType(i);
            final Class<?> toParamType = toType.parameterType(i);
            if(canAutoConvert(fromParamType, toParamType)) {
                newHandle = applyConverters(newHandle, pos, converters);
            } else {
                final MethodHandle converter = getTypeConverterNull(fromParamType, toParamType);
                if(converter != null) {
                    if(converters.isEmpty()) {
                        pos = i;
                    }
                    converters.add(converter);
                } else {
                    newHandle = applyConverters(newHandle, pos, converters);
                }
            }
        }
        newHandle = applyConverters(newHandle, pos, converters);

        // Convert return type
        final Class<?> fromRetType = fromType.returnType();
        final Class<?> toRetType = toType.returnType();
        if(fromRetType != Void.TYPE && toRetType != Void.TYPE) {
            if(!canAutoConvert(toRetType, fromRetType)) {
                final MethodHandle converter = getTypeConverterNull(toRetType, fromRetType);
                if(converter != null) {
                    newHandle = MethodHandles.filterReturnValue(newHandle, converter);
                }
            }
        }

        // Give change to automatic conversion strategy, if one is present.
        final MethodHandle autoConvertedHandle =
                autoConversionStrategy != null ? autoConversionStrategy.asType(newHandle, fromType) : newHandle;

        // Do a final asType for any conversions that remain.
        return autoConvertedHandle.asType(fromType);
    }

    private static MethodHandle applyConverters(final MethodHandle handle, final int pos, final List<MethodHandle> converters) {
        if(converters.isEmpty()) {
            return handle;
        }
        final MethodHandle newHandle =
                MethodHandles.filterArguments(handle, pos, converters.toArray(new MethodHandle[0]));
        converters.clear();
        return newHandle;
    }

    /**
     * Returns true if there might exist a conversion between the requested types (either an automatic JVM conversion,
     * or one provided by any available {@link GuardingTypeConverterFactory}), or false if there definitely does not
     * exist a conversion between the requested types. Note that returning true does not guarantee that the conversion
     * will succeed at runtime (notably, if the "from" or "to" types are sufficiently generic), but returning false
     * guarantees that it would fail.
     *
     * @param from the source type for the conversion
     * @param to the target type for the conversion
     * @return true if there can be a conversion, false if there can not.
     */
    boolean canConvert(final Class<?> from, final Class<?> to) {
        return canAutoConvert(from, to) || canConvert.get(from).get(to);
    }

    /**
     * Determines which of the two type conversions from a source type to the two target types is preferred. This is
     * used for dynamic overloaded method resolution. If the source type is convertible to exactly one target type with
     * a method invocation conversion, it is chosen, otherwise available {@link ConversionComparator}s are consulted.
     * @param sourceType the source type.
     * @param targetType1 one potential target type
     * @param targetType2 another potential target type.
     * @return one of Comparison constants that establish which - if any - of the target types is preferable for the
     * conversion.
     */
    Comparison compareConversion(final Class<?> sourceType, final Class<?> targetType1, final Class<?> targetType2) {
        for(final ConversionComparator comparator: comparators) {
            final Comparison result = comparator.compareConversion(sourceType, targetType1, targetType2);
            if(result != Comparison.INDETERMINATE) {
                return result;
            }
        }
        if(TypeUtilities.isMethodInvocationConvertible(sourceType, targetType1)) {
            if(!TypeUtilities.isMethodInvocationConvertible(sourceType, targetType2)) {
                return Comparison.TYPE_1_BETTER;
            }
        } else if(TypeUtilities.isMethodInvocationConvertible(sourceType, targetType2)) {
            return Comparison.TYPE_2_BETTER;
        }
        return Comparison.INDETERMINATE;
    }

    /**
     * Determines whether it's safe to perform an automatic conversion between the source and target class.
     *
     * @param fromType convert from this class
     * @param toType convert to this class
     * @return true if it's safe to let MethodHandles.convertArguments() to handle this conversion.
     */
    /*private*/ static boolean canAutoConvert(final Class<?> fromType, final Class<?> toType) {
        return TypeUtilities.isMethodInvocationConvertible(fromType, toType);
    }

    /*private*/ MethodHandle getCacheableTypeConverterNull(final Class<?> sourceType, final Class<?> targetType) {
        final MethodHandle converter = getCacheableTypeConverter(sourceType, targetType);
        return converter == IDENTITY_CONVERSION ? null : converter;
    }

    /*private*/ MethodHandle getTypeConverterNull(final Class<?> sourceType, final Class<?> targetType) {
        try {
            return getCacheableTypeConverterNull(sourceType, targetType);
        } catch(final NotCacheableConverter e) {
            return e.converter;
        }
    }

    /*private*/ MethodHandle getCacheableTypeConverter(final Class<?> sourceType, final Class<?> targetType) {
        return converterMap.get(sourceType).get(targetType);
    }

    /**
     * Given a source and target type, returns a method handle that converts between them. Never returns null; in worst
     * case it will return an identity conversion (that might fail for some values at runtime). You can use this method
     * if you have a piece of your program that is written in Java, and you need to reuse existing type conversion
     * machinery in a non-invokedynamic context.
     * @param sourceType the type to convert from
     * @param targetType the type to convert to
     * @return a method handle performing the conversion.
     */
    MethodHandle getTypeConverter(final Class<?> sourceType, final Class<?> targetType) {
        try {
            return converterIdentityMap.get(sourceType).get(targetType);
        } catch(final NotCacheableConverter e) {
            return e.converter;
        }
    }

    private static class LookupSupplier implements Supplier<MethodHandles.Lookup> {
        volatile boolean returnedLookup;
        volatile boolean closed;

        @Override
        public Lookup get() {
            if (closed) {
                // Something held on to this supplier and tried to invoke it
                // after we're done with it.
                throw new IllegalStateException();
            }
            final Lookup lookup = LinkerServicesImpl.getCurrentLookup();
            returnedLookup = true;
            return lookup;
        }
    }

    /*private*/ MethodHandle createConverter(final Class<?> sourceType, final Class<?> targetType) throws Exception {
        final MethodType type = MethodType.methodType(targetType, sourceType);
        final MethodHandle identity = IDENTITY_CONVERSION.asType(type);
        MethodHandle last = identity;

        final LookupSupplier lookupSupplier = new LookupSupplier();
        try {
            for(int i = factories.length; i-- > 0;) {
                final GuardedInvocation next = factories[i].convertToType(sourceType, targetType, lookupSupplier);
                if(next != null) {
                    last = next.compose(last);
                }
            }
        } finally {
            lookupSupplier.closed = true;
        }

        if(last == identity) {
            return IDENTITY_CONVERSION;
        }
        if(!lookupSupplier.returnedLookup) {
            return last;
        }
        // At least one of the consulted converter factories obtained the
        // lookup, so we must presume the created converter is sensitive to the
        // lookup class and thus we will not cache it.
        throw new NotCacheableConverter(last);
    }

    /*private*/ static final MethodHandle IDENTITY_CONVERSION = MethodHandles.identity(Object.class);

    @SuppressWarnings("serial")
    private static class NotCacheableConverter extends RuntimeException {
        final MethodHandle converter;

        NotCacheableConverter(final MethodHandle converter) {
            super("", null, false, false);
            this.converter = converter;
        }
    }
}