linker/support/Guards.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:

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       modification, are permitted provided that the following conditions are
       met:
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         notice, this list of conditions and the following disclaimer.
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         notice, this list of conditions and the following disclaimer in the
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package jdk.dynalink.linker.support;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.util.logging.Level;
import java.util.logging.Logger;
import jdk.dynalink.DynamicLinker;
import jdk.dynalink.linker.LinkerServices;

/**
 * Utility methods for creating typical guards for
 * {@link MethodHandles#guardWithTest(MethodHandle, MethodHandle, MethodHandle)}
 * and for adjusting their method types.
 */
public final class Guards {
    private static final Logger LOG = Logger
            .getLogger(Guards.class.getName(), "jdk.dynalink.support.messages");

    private Guards() {
    }

    /**
     * Creates a guard method handle with arguments of a specified type, but with boolean return value. When invoked, it
     * returns true if the first argument is of the specified class (exactly of it, not a subclass). The rest of the
     * arguments will be ignored.
     *
     * @param clazz the class of the first argument to test for
     * @param type the method type
     * @return a method handle testing whether its first argument is of the specified class.
     */
    @SuppressWarnings("boxing")
    public static MethodHandle isOfClass(final Class<?> clazz, final MethodType type) {
        final Class<?> declaredType = type.parameterType(0);
        if(clazz == declaredType) {
            LOG.log(Level.WARNING, "isOfClassGuardAlwaysTrue", new Object[] { clazz.getName(), 0, type, DynamicLinker.getLinkedCallSiteLocation() });
            return constantTrue(type);
        }
        if(!declaredType.isAssignableFrom(clazz)) {
            LOG.log(Level.WARNING, "isOfClassGuardAlwaysFalse", new Object[] { clazz.getName(), 0, type, DynamicLinker.getLinkedCallSiteLocation() });
            return constantFalse(type);
        }
        return getClassBoundArgumentTest(IS_OF_CLASS, clazz, 0, type);
    }

    /**
     * Creates a method handle with arguments of a specified type, but with boolean return value. When invoked, it
     * returns true if the first argument is instance of the specified class or its subclass). The rest of the arguments
     * will be ignored.
     *
     * @param clazz the class of the first argument to test for
     * @param type the method type
     * @return a method handle testing whether its first argument is of the specified class or subclass.
     */
    public static MethodHandle isInstance(final Class<?> clazz, final MethodType type) {
        return isInstance(clazz, 0, type);
    }

    /**
     * Creates a method handle with arguments of a specified type, but with boolean return value. When invoked, it
     * returns true if the n'th argument is instance of the specified class or its subclass). The rest of the arguments
     * will be ignored.
     *
     * @param clazz the class of the first argument to test for
     * @param pos the position on the argument list to test
     * @param type the method type
     * @return a method handle testing whether its first argument is of the specified class or subclass.
     */
    @SuppressWarnings("boxing")
    public static MethodHandle isInstance(final Class<?> clazz, final int pos, final MethodType type) {
        final Class<?> declaredType = type.parameterType(pos);
        if(clazz.isAssignableFrom(declaredType)) {
            LOG.log(Level.WARNING, "isInstanceGuardAlwaysTrue", new Object[] { clazz.getName(), pos, type, DynamicLinker.getLinkedCallSiteLocation() });
            return constantTrue(type);
        }
        if(!declaredType.isAssignableFrom(clazz)) {
            LOG.log(Level.WARNING, "isInstanceGuardAlwaysFalse", new Object[] { clazz.getName(), pos, type, DynamicLinker.getLinkedCallSiteLocation() });
            return constantFalse(type);
        }
        return getClassBoundArgumentTest(IS_INSTANCE, clazz, pos, type);
    }

    /**
     * Creates a method handle that returns true if the argument in the specified position is a Java array.
     *
     * @param pos the position in the argument lit
     * @param type the method type of the handle
     * @return a method handle that returns true if the argument in the specified position is a Java array; the rest of
     * the arguments are ignored.
     */
    @SuppressWarnings("boxing")
    public static MethodHandle isArray(final int pos, final MethodType type) {
        final Class<?> declaredType = type.parameterType(pos);
        if(declaredType.isArray()) {
            LOG.log(Level.WARNING, "isArrayGuardAlwaysTrue", new Object[] { pos, type, DynamicLinker.getLinkedCallSiteLocation() });
            return constantTrue(type);
        }
        if(!declaredType.isAssignableFrom(Object[].class)) {
            LOG.log(Level.WARNING, "isArrayGuardAlwaysFalse", new Object[] { pos, type, DynamicLinker.getLinkedCallSiteLocation() });
            return constantFalse(type);
        }
        return asType(IS_ARRAY, pos, type);
    }

    private static MethodHandle getClassBoundArgumentTest(final MethodHandle test, final Class<?> clazz, final int pos, final MethodType type) {
        // Bind the class to the first argument of the test
        return asType(test.bindTo(clazz), pos, type);
    }

    /**
     * Takes a method handle intended to be used as a guard, and adapts it to
     * the requested type, but returning a boolean. Applies
     * {@link MethodHandle#asType(MethodType)} to convert types and uses
     * {@link MethodHandles#dropArguments(MethodHandle, int, Class...)} to match
     * the requested type arity.
     * @param test the test method handle
     * @param type the type to adapt the method handle to
     * @return the adapted method handle
     */
    public static MethodHandle asType(final MethodHandle test, final MethodType type) {
        return test.asType(getTestType(test, type));
    }

    /**
     * Takes a method handle intended to be used as a guard, and adapts it to
     * the requested type, but returning a boolean. Applies
     * {@link LinkerServices#asType(MethodHandle, MethodType)} to convert types
     * and uses
     * {@link MethodHandles#dropArguments(MethodHandle, int, Class...)} to match
     * the requested type arity.
     * @param linkerServices the linker services to use for type conversions
     * @param test the test method handle
     * @param type the type to adapt the method handle to
     * @return the adapted method handle
     */
    public static MethodHandle asType(final LinkerServices linkerServices, final MethodHandle test, final MethodType type) {
        return linkerServices.asType(test, getTestType(test, type));
    }

    private static MethodType getTestType(final MethodHandle test, final MethodType type) {
        return type.dropParameterTypes(test.type().parameterCount(),
                type.parameterCount()).changeReturnType(boolean.class);
    }

    private static MethodHandle asType(final MethodHandle test, final int pos, final MethodType type) {
        assert test != null;
        assert type != null;
        assert type.parameterCount() > 0;
        assert pos >= 0 && pos < type.parameterCount();
        assert test.type().parameterCount() == 1;
        assert test.type().returnType() == Boolean.TYPE;
        return MethodHandles.permuteArguments(test.asType(test.type().changeParameterType(0, type.parameterType(pos))),
                type.changeReturnType(Boolean.TYPE), new int[] { pos });
    }

    private static final MethodHandle IS_INSTANCE = Lookup.PUBLIC.findVirtual(Class.class, "isInstance",
            MethodType.methodType(Boolean.TYPE, Object.class));

    private static final MethodHandle IS_OF_CLASS;
    private static final MethodHandle IS_ARRAY;
    private static final MethodHandle IS_IDENTICAL;
    private static final MethodHandle IS_NULL;
    private static final MethodHandle IS_NOT_NULL;

    static {
        final Lookup lookup = new Lookup(MethodHandles.lookup());

        IS_OF_CLASS  = lookup.findOwnStatic("isOfClass",   Boolean.TYPE, Class.class, Object.class);
        IS_ARRAY     = lookup.findOwnStatic("isArray",     Boolean.TYPE, Object.class);
        IS_IDENTICAL = lookup.findOwnStatic("isIdentical", Boolean.TYPE, Object.class, Object.class);
        IS_NULL      = lookup.findOwnStatic("isNull",      Boolean.TYPE, Object.class);
        IS_NOT_NULL  = lookup.findOwnStatic("isNotNull",   Boolean.TYPE, Object.class);
    }

    /**
     * Creates a guard method that tests its only argument for being of an exact particular class.
     * @param clazz the class to test for.
     * @return the desired guard method.
     */
    public static MethodHandle getClassGuard(final Class<?> clazz) {
        return IS_OF_CLASS.bindTo(clazz);
    }

    /**
     * Creates a guard method that tests its only argument for being an instance of a particular class.
     * @param clazz the class to test for.
     * @return the desired guard method.
     */
    public static MethodHandle getInstanceOfGuard(final Class<?> clazz) {
        return IS_INSTANCE.bindTo(clazz);
    }

    /**
     * Creates a guard method that tests its only argument for being referentially identical to another object
     * @param obj the object used as referential identity test
     * @return the desired guard method.
     */
    public static MethodHandle getIdentityGuard(final Object obj) {
        return IS_IDENTICAL.bindTo(obj);
    }

    /**
     * Returns a guard that tests whether the first argument is null.
     * @return a guard that tests whether the first argument is null.
     */
    public static MethodHandle isNull() {
        return IS_NULL;
    }

    /**
     * Returns a guard that tests whether the first argument is not null.
     * @return a guard that tests whether the first argument is not null.
     */
    public static MethodHandle isNotNull() {
        return IS_NOT_NULL;
    }

    @SuppressWarnings("unused")
    private static boolean isNull(final Object obj) {
        return obj == null;
    }

    @SuppressWarnings("unused")
    private static boolean isNotNull(final Object obj) {
        return obj != null;
    }

    @SuppressWarnings("unused")
    private static boolean isArray(final Object o) {
        return o != null && o.getClass().isArray();
    }

    @SuppressWarnings("unused")
    private static boolean isOfClass(final Class<?> c, final Object o) {
        return o != null && o.getClass() == c;
    }

    @SuppressWarnings("unused")
    private static boolean isIdentical(final Object o1, final Object o2) {
        return o1 == o2;
    }

    private static MethodHandle constantTrue(final MethodType type) {
        return constantBoolean(Boolean.TRUE, type);
    }

    private static MethodHandle constantFalse(final MethodType type) {
        return constantBoolean(Boolean.FALSE, type);
    }

    private static MethodHandle constantBoolean(final Boolean value, final MethodType type) {
        return MethodHandles.permuteArguments(MethodHandles.constant(Boolean.TYPE, value),
                type.changeReturnType(Boolean.TYPE));
    }
}