JDK14/Java14源码在线阅读

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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 * 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).
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package jdk.nashorn.internal.runtime.linker;

import static jdk.nashorn.internal.lookup.Lookup.MH;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.lang.reflect.Modifier;
import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Collection;
import java.util.Deque;
import java.util.List;
import java.util.Map;
import java.util.Queue;
import java.util.function.Supplier;
import javax.script.Bindings;
import jdk.dynalink.CallSiteDescriptor;
import jdk.dynalink.SecureLookupSupplier;
import jdk.dynalink.linker.ConversionComparator;
import jdk.dynalink.linker.GuardedInvocation;
import jdk.dynalink.linker.GuardingTypeConverterFactory;
import jdk.dynalink.linker.LinkRequest;
import jdk.dynalink.linker.LinkerServices;
import jdk.dynalink.linker.TypeBasedGuardingDynamicLinker;
import jdk.dynalink.linker.support.Guards;
import jdk.dynalink.linker.support.Lookup;
import jdk.nashorn.api.scripting.JSObject;
import jdk.nashorn.api.scripting.ScriptObjectMirror;
import jdk.nashorn.api.scripting.ScriptUtils;
import jdk.nashorn.internal.codegen.CompilerConstants.Call;
import jdk.nashorn.internal.objects.NativeArray;
import jdk.nashorn.internal.runtime.AccessControlContextFactory;
import jdk.nashorn.internal.runtime.JSType;
import jdk.nashorn.internal.runtime.ListAdapter;
import jdk.nashorn.internal.runtime.ScriptFunction;
import jdk.nashorn.internal.runtime.ScriptObject;
import jdk.nashorn.internal.runtime.Undefined;

/**
 * This is the main dynamic linker for Nashorn. It is used for linking all {@link ScriptObject} and its subclasses (this
 * includes {@link ScriptFunction} and its subclasses) as well as {@link Undefined}.
 */
final class NashornLinker implements TypeBasedGuardingDynamicLinker, GuardingTypeConverterFactory, ConversionComparator {
    private static final AccessControlContext GET_LOOKUP_PERMISSION_CONTEXT =
            AccessControlContextFactory.createAccessControlContext(SecureLookupSupplier.GET_LOOKUP_PERMISSION_NAME);

    private static final ClassValue<MethodHandle> ARRAY_CONVERTERS = new ClassValue<MethodHandle>() {
        @Override
        protected MethodHandle computeValue(final Class<?> type) {
            return createArrayConverter(type);
        }
    };

    /**
     * Returns true if {@code ScriptObject} is assignable from {@code type}, or it is {@code Undefined}.
     */
    @Override
    public boolean canLinkType(final Class<?> type) {
        return canLinkTypeStatic(type);
    }

    static boolean canLinkTypeStatic(final Class<?> type) {
        return ScriptObject.class.isAssignableFrom(type) || Undefined.class == type;
    }

    @Override
    public GuardedInvocation getGuardedInvocation(final LinkRequest request, final LinkerServices linkerServices) throws Exception {
        final CallSiteDescriptor desc = request.getCallSiteDescriptor();
        return Bootstrap.asTypeSafeReturn(getGuardedInvocation(request, desc), linkerServices, desc);
    }

    private static GuardedInvocation getGuardedInvocation(final LinkRequest request, final CallSiteDescriptor desc) {
        final Object self = request.getReceiver();

        final GuardedInvocation inv;
        if (self instanceof ScriptObject) {
            inv = ((ScriptObject)self).lookup(desc, request);
        } else if (self instanceof Undefined) {
            inv = Undefined.lookup(desc);
        } else {
            throw new AssertionError(self.getClass().getName()); // Should never reach here.
        }

        return inv;
    }

    @Override
    public GuardedInvocation convertToType(final Class<?> sourceType, final Class<?> targetType, final Supplier<MethodHandles.Lookup> lookupSupplier) throws Exception {
        GuardedInvocation gi = convertToTypeNoCast(sourceType, targetType, lookupSupplier);
        if(gi == null) {
            gi = getSamTypeConverter(sourceType, targetType, lookupSupplier);
        }
        return gi == null ? null : gi.asType(MH.type(targetType, sourceType));
    }

    /**
     * Main part of the implementation of {@link GuardingTypeConverterFactory#convertToType(Class, Class)} that doesn't
     * care about adapting the method signature; that's done by the invoking method. Returns either a built-in
     * conversion to primitive (or primitive wrapper) Java types or to String, or a just-in-time generated converter to
     * a SAM type (if the target type is a SAM type).
     * @param sourceType the source type
     * @param targetType the target type
     * @return a guarded invocation that converts from the source type to the target type.
     * @throws Exception if something goes wrong
     */
    private static GuardedInvocation convertToTypeNoCast(final Class<?> sourceType, final Class<?> targetType, final Supplier<MethodHandles.Lookup> lookupSupplier) throws Exception {
        final MethodHandle mh = JavaArgumentConverters.getConverter(targetType);
        if (mh != null) {
            return new GuardedInvocation(mh, canLinkTypeStatic(sourceType) ? null : IS_NASHORN_OR_UNDEFINED_TYPE);
        }

        final GuardedInvocation arrayConverter = getArrayConverter(sourceType, targetType, lookupSupplier);
        if(arrayConverter != null) {
            return arrayConverter;
        }

        return getMirrorConverter(sourceType, targetType);
    }

    /**
     * Returns a guarded invocation that converts from a source type that is ScriptFunction, or a subclass or a
     * superclass of it) to a SAM type.
     * @param sourceType the source type (presumably ScriptFunction or a subclass or a superclass of it)
     * @param targetType the target type (presumably a SAM type)
     * @return a guarded invocation that converts from the source type to the target SAM type. null is returned if
     * either the source type is neither ScriptFunction, nor a subclass, nor a superclass of it, or if the target type
     * is not a SAM type.
     * @throws Exception if something goes wrong; generally, if there's an issue with creation of the SAM proxy type
     * constructor.
     */
    private static GuardedInvocation getSamTypeConverter(final Class<?> sourceType, final Class<?> targetType, final Supplier<MethodHandles.Lookup> lookupSupplier) throws Exception {
        // If source type is more generic than ScriptFunction class, we'll need to use a guard
        final boolean isSourceTypeGeneric = sourceType.isAssignableFrom(ScriptObject.class);

        if ((isSourceTypeGeneric || ScriptFunction.class.isAssignableFrom(sourceType)) && isAutoConvertibleFromFunction(targetType)) {
            final Class<?> paramType = isSourceTypeGeneric ? Object.class : ScriptFunction.class;
            // Using Object.class as constructor source type means we're getting an overloaded constructor handle,
            // which is safe but slower than a single constructor handle. If the actual argument is a ScriptFunction it
            // would be nice if we could change the formal parameter to ScriptFunction.class and add a guard for it
            // in the main invocation.
            final MethodHandle ctor = JavaAdapterFactory.getConstructor(paramType, targetType, getCurrentLookup(lookupSupplier));
            assert ctor != null; // if isAutoConvertibleFromFunction() returned true, then ctor must exist.
            return new GuardedInvocation(ctor, isSourceTypeGeneric ? IS_FUNCTION : null);
        }
        return null;
    }

    private static MethodHandles.Lookup getCurrentLookup(final Supplier<MethodHandles.Lookup> lookupSupplier) {
        return AccessController.doPrivileged(new PrivilegedAction<MethodHandles.Lookup>() {
            @Override
            public MethodHandles.Lookup run() {
                return lookupSupplier.get();
            }
        }, GET_LOOKUP_PERMISSION_CONTEXT);
    }

    /**
     * Returns a guarded invocation that converts from a source type that is NativeArray to a Java array or List or
     * Queue or Deque or Collection type.
     * @param sourceType the source type (presumably NativeArray a superclass of it)
     * @param targetType the target type (presumably an array type, or List or Queue, or Deque, or Collection)
     * @return a guarded invocation that converts from the source type to the target type. null is returned if
     * either the source type is neither NativeArray, nor a superclass of it, or if the target type is not an array
     * type, List, Queue, Deque, or Collection.
     */
    private static GuardedInvocation getArrayConverter(final Class<?> sourceType, final Class<?> targetType, final Supplier<MethodHandles.Lookup> lookupSupplier) {
        final boolean isSourceTypeNativeArray = sourceType == NativeArray.class;
        // If source type is more generic than NativeArray class, we'll need to use a guard
        final boolean isSourceTypeGeneric = !isSourceTypeNativeArray && sourceType.isAssignableFrom(NativeArray.class);

        if (isSourceTypeNativeArray || isSourceTypeGeneric) {
            final MethodHandle guard = isSourceTypeGeneric ? IS_NATIVE_ARRAY : null;
            if(targetType.isArray()) {
                final MethodHandle mh = ARRAY_CONVERTERS.get(targetType);
                final MethodHandle mhWithLookup;
                if (mh.type().parameterCount() == 2) {
                    assert mh.type().parameterType(1) == SecureLookupSupplier.class;
                    // We enter this branch when the array's ultimate component
                    // type is a SAM type; we use a handle to JSType.toJavaArrayWithLookup
                    // for these in the converter MH and must bind it here with
                    // a secure supplier for the current lookup. By retrieving
                    // the lookup, we'll also (correctly) inform the type
                    // converter that this array converter is lookup specific.
                    // We then need to wrap the returned lookup into a
                    // new SecureLookupSupplier in order to bind it to the
                    // JSType.toJavaArrayWithLookup() parameter.
                    mhWithLookup = MH.insertArguments(mh, 1,
                            new SecureLookupSupplier(getCurrentLookup(lookupSupplier)));
                } else {
                    mhWithLookup = mh;
                }
                return new GuardedInvocation(mhWithLookup, guard);
            } else if(targetType == List.class) {
                return new GuardedInvocation(TO_LIST, guard);
            } else if(targetType == Deque.class) {
                return new GuardedInvocation(TO_DEQUE, guard);
            } else if(targetType == Queue.class) {
                return new GuardedInvocation(TO_QUEUE, guard);
            } else if(targetType == Collection.class) {
                return new GuardedInvocation(TO_COLLECTION, guard);
            }
        }
        return null;
    }

    private static MethodHandle createArrayConverter(final Class<?> type) {
        assert type.isArray();

        final Class<?> componentType = type.getComponentType();
        final Call converterCall;
        // Is the ultimate component type of this array a SAM type?
        if (isComponentTypeAutoConvertibleFromFunction(componentType)) {
            converterCall = JSType.TO_JAVA_ARRAY_WITH_LOOKUP;
        } else {
            converterCall = JSType.TO_JAVA_ARRAY;
        }
        final MethodHandle typeBoundConverter = MH.insertArguments(converterCall.methodHandle(), 1, componentType);
        return MH.asType(typeBoundConverter, typeBoundConverter.type().changeReturnType(type));
    }

    private static boolean isComponentTypeAutoConvertibleFromFunction(final Class<?> targetType) {
        if (targetType.isArray()) {
            return isComponentTypeAutoConvertibleFromFunction(targetType.getComponentType());
        }
        return isAutoConvertibleFromFunction(targetType);
    }

    private static GuardedInvocation getMirrorConverter(final Class<?> sourceType, final Class<?> targetType) {
        // Could've also used (targetType.isAssignableFrom(ScriptObjectMirror.class) && targetType != Object.class) but
        // it's probably better to explicitly spell out the supported target types
        if (targetType == Map.class || targetType == Bindings.class || targetType == JSObject.class || targetType == ScriptObjectMirror.class) {
            if (ScriptObject.class.isAssignableFrom(sourceType)) {
                return new GuardedInvocation(CREATE_MIRROR);
            } else if (sourceType.isAssignableFrom(ScriptObject.class) || sourceType.isInterface()) {
                return new GuardedInvocation(CREATE_MIRROR, IS_SCRIPT_OBJECT);
            }
        }
        return null;
    }

    private static boolean isAutoConvertibleFromFunction(final Class<?> clazz) {
        return isAbstractClass(clazz) && !ScriptObject.class.isAssignableFrom(clazz) &&
                JavaAdapterFactory.isAutoConvertibleFromFunction(clazz);
    }

    /**
     * Utility method used by few other places in the code. Tests if the class has the abstract modifier and is not an
     * array class. For some reason, array classes have the abstract modifier set in HotSpot JVM, and we don't want to
     * treat array classes as abstract.
     * @param clazz the inspected class
     * @return true if the class is abstract and is not an array type.
     */
    static boolean isAbstractClass(final Class<?> clazz) {
        return Modifier.isAbstract(clazz.getModifiers()) && !clazz.isArray();
    }


    @Override
    public Comparison compareConversion(final Class<?> sourceType, final Class<?> targetType1, final Class<?> targetType2) {
        if(sourceType == NativeArray.class) {
            // Prefer those types we can convert to with just a wrapper (cheaper than Java array creation).
            if(isArrayPreferredTarget(targetType1)) {
                if(!isArrayPreferredTarget(targetType2)) {
                    return Comparison.TYPE_1_BETTER;
                }
            } else if(isArrayPreferredTarget(targetType2)) {
                return Comparison.TYPE_2_BETTER;
            }
            // Then prefer Java arrays
            if(targetType1.isArray()) {
                if(!targetType2.isArray()) {
                    return Comparison.TYPE_1_BETTER;
                }
            } else if(targetType2.isArray()) {
                return Comparison.TYPE_2_BETTER;
            }
        }
        if(ScriptObject.class.isAssignableFrom(sourceType)) {
            // Prefer interfaces
            if(targetType1.isInterface()) {
                if(!targetType2.isInterface()) {
                    return Comparison.TYPE_1_BETTER;
                }
            } else if(targetType2.isInterface()) {
                return Comparison.TYPE_2_BETTER;
            }
        }
        return Comparison.INDETERMINATE;
    }

    private static boolean isArrayPreferredTarget(final Class<?> clazz) {
        return clazz == List.class || clazz == Collection.class || clazz == Queue.class || clazz == Deque.class;
    }

    private static final MethodHandle IS_SCRIPT_OBJECT = Guards.isInstance(ScriptObject.class, MH.type(Boolean.TYPE, Object.class));
    private static final MethodHandle IS_FUNCTION = findOwnMH("isFunction", boolean.class, Object.class);
    private static final MethodHandle IS_NATIVE_ARRAY = Guards.isOfClass(NativeArray.class, MH.type(Boolean.TYPE, Object.class));


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