Java example source code file (Guards.java)

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class, classloader, guards, is_array, is_identical, is_not_null, is_null, is_of_class, log, logger, logging, lookup, methodhandle, methodtype, object, suppresswarnings

The Guards.java Java example source code

/*
 * 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

/*
 * 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:
 */
/*
   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
       SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
       BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
       WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
       OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
       ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

package jdk.internal.dynalink.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.internal.dynalink.DynamicLinker;
import jdk.internal.dynalink.linker.LinkerServices;

/**
 * Utility methods for creating typical guards. TODO: introduce reasonable caching of created guards.
 *
 * @author Attila Szegedi
 */
public class Guards {
    private static final Logger LOG = Logger
            .getLogger(Guards.class.getName(), "jdk.internal.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(Class<?> clazz, 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(Class<?> clazz, 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(Class<?> clazz, int pos, 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(int pos, 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);
    }

    /**
     * Return true if it is safe to strongly reference a class from the referred class loader from a class associated
     * with the referring class loader without risking a class loader memory leak.
     *
     * @param referrerLoader the referrer class loader
     * @param referredLoader the referred class loader
     * @return true if it is safe to strongly reference the class
     */
    public static boolean canReferenceDirectly(ClassLoader referrerLoader, final ClassLoader referredLoader) {
        if(referredLoader == null) {
            // Can always refer directly to a system class
            return true;
        }
        if(referrerLoader == null) {
            // System classes can't refer directly to any non-system class
            return false;
        }
        // Otherwise, can only refer directly to classes residing in same or
        // parent class loader.

        ClassLoader referrer = referrerLoader;
        do {
            if(referrer == referredLoader) {
                return true;
            }
            referrer = referrer.getParent();
        } while(referrer != null);
        return false;
    }

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

    /**
     * Takes a guard-test method handle, and adapts it to the requested type, returning a boolean. Only applies
     * conversions as per {@link MethodHandle#asType(MethodType)}.
     * @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(MethodHandle test, MethodType type) {
        return test.asType(getTestType(test, type));
    }

    /**
     * Takes a guard-test method handle, and adapts it to the requested type, returning a boolean. Applies the passed
     * {@link LinkerServices} object's {@link LinkerServices#asType(MethodHandle, MethodType)}.
     * @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(LinkerServices linkerServices, MethodHandle test, MethodType type) {
        return linkerServices.asType(test, getTestType(test, type));
    }

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

    private static MethodHandle asType(MethodHandle test, int pos, 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(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(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(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(Object obj) {
        return obj == null;
    }

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

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

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

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

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

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

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