Java example source code file (JavaSuperAdapterLinker.java)

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Java - Java tags/keywords

bind_dynamic_method, callsitedescriptor, dyn_get_method, dyn_get_method_fixed, get_adapter, guardedinvocation, is_adapter_of_class, javasuperadapter, methodhandle, methodtype, object, override, string, suppresswarnings

The JavaSuperAdapterLinker.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.
 */

package jdk.nashorn.internal.runtime.linker;

import static jdk.nashorn.internal.lookup.Lookup.EMPTY_GETTER;
import static jdk.nashorn.internal.runtime.linker.JavaAdapterBytecodeGenerator.SUPER_PREFIX;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import jdk.internal.dynalink.CallSiteDescriptor;
import jdk.internal.dynalink.beans.BeansLinker;
import jdk.internal.dynalink.linker.GuardedInvocation;
import jdk.internal.dynalink.linker.LinkRequest;
import jdk.internal.dynalink.linker.LinkerServices;
import jdk.internal.dynalink.linker.TypeBasedGuardingDynamicLinker;
import jdk.internal.dynalink.support.CallSiteDescriptorFactory;
import jdk.internal.dynalink.support.Lookup;
import jdk.nashorn.internal.runtime.ScriptRuntime;

/**
 * A linker for instances of {@link JavaSuperAdapter}. Only links {@code getMethod} calls, by forwarding them to the
 * bean linker for the adapter class and prepending {@code super$} to method names.
 *
 */
final class JavaSuperAdapterLinker implements TypeBasedGuardingDynamicLinker {
    private static final String GET_METHOD = "getMethod";
    private static final String DYN_GET_METHOD = "dyn:" + GET_METHOD;
    private static final String DYN_GET_METHOD_FIXED = DYN_GET_METHOD + ":" + SUPER_PREFIX;

    private static final MethodHandle ADD_PREFIX_TO_METHOD_NAME;
    private static final MethodHandle BIND_DYNAMIC_METHOD;
    private static final MethodHandle GET_ADAPTER;
    private static final MethodHandle IS_ADAPTER_OF_CLASS;

    static {
        final Lookup lookup = new Lookup(MethodHandles.lookup());
        ADD_PREFIX_TO_METHOD_NAME = lookup.findOwnStatic("addPrefixToMethodName", Object.class, Object.class);
        BIND_DYNAMIC_METHOD = lookup.findOwnStatic("bindDynamicMethod", Object.class, Object.class, Object.class);
        GET_ADAPTER = lookup.findVirtual(JavaSuperAdapter.class, "getAdapter", MethodType.methodType(Object.class));
        IS_ADAPTER_OF_CLASS = lookup.findOwnStatic("isAdapterOfClass", boolean.class, Class.class, Object.class);
    }

    @Override
    public boolean canLinkType(final Class<?> type) {
        return type == JavaSuperAdapter.class;
    }

    @Override
    public GuardedInvocation getGuardedInvocation(final LinkRequest linkRequest, final LinkerServices linkerServices)
            throws Exception {
        final Object objSuperAdapter = linkRequest.getReceiver();
        if(!(objSuperAdapter instanceof JavaSuperAdapter)) {
            return null;
        }

        final CallSiteDescriptor descriptor = linkRequest.getCallSiteDescriptor();
        if(!CallSiteDescriptorFactory.tokenizeOperators(descriptor).contains(GET_METHOD)) {
            // We only handle getMethod
            return null;
        }

        final Object adapter = ((JavaSuperAdapter)objSuperAdapter).getAdapter();

        // Replace argument (javaSuperAdapter, ...) => (adapter, ...) when delegating to BeansLinker
        final Object[] args = linkRequest.getArguments();
        args[0] = adapter;

        // Use R(T0, ...) => R(adapter.class, ...) call site type when delegating to BeansLinker.
        final MethodType type = descriptor.getMethodType();
        final Class<?> adapterClass = adapter.getClass();
        final boolean hasFixedName = descriptor.getNameTokenCount() > 2;
        final String opName = hasFixedName ? (DYN_GET_METHOD_FIXED + descriptor.getNameToken(
                CallSiteDescriptor.NAME_OPERAND)) : DYN_GET_METHOD;

        final CallSiteDescriptor newDescriptor = NashornCallSiteDescriptor.get(descriptor.getLookup(), opName,
                type.changeParameterType(0, adapterClass), 0);

        // Delegate to BeansLinker
        final GuardedInvocation guardedInv = NashornBeansLinker.getGuardedInvocation(
                BeansLinker.getLinkerForClass(adapterClass), linkRequest.replaceArguments(newDescriptor, args),
                linkerServices);

        final MethodHandle guard = IS_ADAPTER_OF_CLASS.bindTo(adapterClass);
        if(guardedInv == null) {
            // Short circuit the lookup here for non-existent methods by linking an empty getter. If we just returned
            // null instead, BeansLinker would find final methods on the JavaSuperAdapter instead: getClass() and
            // wait().
            return new GuardedInvocation(MethodHandles.dropArguments(EMPTY_GETTER, 1,type.parameterList().subList(1,
                    type.parameterCount())), guard).asType(descriptor);
        }

        final MethodHandle invocation = guardedInv.getInvocation();
        final MethodType invType = invocation.type();
        // For invocation typed R(T0, ...) create a dynamic method binder of type R(R, T0)
        final MethodHandle typedBinder = BIND_DYNAMIC_METHOD.asType(MethodType.methodType(invType.returnType(),
                invType.returnType(), invType.parameterType(0)));
        // For invocation typed R(T0, T1, ...) create a dynamic method binder of type R(R, T0, T1, ...)
        final MethodHandle droppingBinder = MethodHandles.dropArguments(typedBinder, 2,
                invType.parameterList().subList(1, invType.parameterCount()));
        // Finally, fold the invocation into the binder to produce a method handle that will bind every returned
        // DynamicMethod object from dyn:getMethod calls to the actual receiver
        // R(R(T0, T1, ...), T0, T1, ...)
        final MethodHandle bindingInvocation = MethodHandles.foldArguments(droppingBinder, invocation);

        final MethodHandle typedGetAdapter = asFilterType(GET_ADAPTER, 0, invType, type);
        final MethodHandle adaptedInvocation;
        if(hasFixedName) {
            adaptedInvocation = MethodHandles.filterArguments(bindingInvocation, 0, typedGetAdapter);
        } else {
            // Add a filter that'll prepend "super$" to each name passed to the variable-name "dyn:getMethod".
            final MethodHandle typedAddPrefix = asFilterType(ADD_PREFIX_TO_METHOD_NAME, 1, invType, type);
            adaptedInvocation = MethodHandles.filterArguments(bindingInvocation, 0, typedGetAdapter, typedAddPrefix);
        }

        return guardedInv.replaceMethods(adaptedInvocation, guard).asType(descriptor);
    }

    /**
     * Adapts the type of a method handle used as a filter in a position from a source method type to a target method type.
     * @param filter the filter method handle
     * @param pos the position in the argument list that it's filtering
     * @param targetType the target method type for filtering
     * @param sourceType the source method type for filtering
     * @return a type adapted filter
     */
    private static MethodHandle asFilterType(final MethodHandle filter, int pos, MethodType targetType, MethodType sourceType) {
        return filter.asType(MethodType.methodType(targetType.parameterType(pos), sourceType.parameterType(pos)));
    }

    @SuppressWarnings("unused")
    private static Object addPrefixToMethodName(final Object name) {
        return SUPER_PREFIX.concat(String.valueOf(name));
    }

    /**
     * Used to transform the return value of getMethod; transform a {@code DynamicMethod} into a
     * {@code BoundDynamicMethod} while also accounting for the possibility of a non-existent method.
     * @param dynamicMethod the dynamic method to bind
     * @param boundThis the adapter underlying a super adapter, to which the dynamic method is bound.
     * @return a dynamic method bound to the adapter instance.
     */
    @SuppressWarnings("unused")
    private static Object bindDynamicMethod(final Object dynamicMethod, final Object boundThis) {
        return dynamicMethod == null ? ScriptRuntime.UNDEFINED : Bootstrap.bindDynamicMethod(dynamicMethod, boundThis);
    }

    /**
     * Used as the guard of linkages, as the receiver is not guaranteed to be a JavaSuperAdapter.
     * @param clazz the class the receiver's adapter is tested against.
     * @param obj receiver
     * @return true if the receiver is a super adapter, and its underlying adapter is of the specified class
     */
    @SuppressWarnings("unused")
    private static boolean isAdapterOfClass(Class<?> clazz, Object obj) {
        return obj instanceof JavaSuperAdapter && clazz == (((JavaSuperAdapter)obj).getAdapter()).getClass();
    }
}