package org.apache.lucene.util;
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the 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.
*/
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.lang.ref.Reference;
import java.lang.ref.WeakReference;
/**
* An AttributeFactory creates instances of {@link AttributeImpl}s.
*/
public abstract class AttributeFactory {
/**
* Returns an {@link AttributeImpl} for the supplied {@link Attribute} interface class.
*/
public abstract AttributeImpl createAttributeInstance(Class<? extends Attribute> attClass);
/**
* Returns a correctly typed {@link MethodHandle} for the no-arg ctor of the given class.
*/
static final MethodHandle findAttributeImplCtor(Class<? extends AttributeImpl> clazz) {
try {
return lookup.findConstructor(clazz, NO_ARG_CTOR).asType(NO_ARG_RETURNING_ATTRIBUTEIMPL);
} catch (NoSuchMethodException | IllegalAccessException e) {
throw new IllegalArgumentException("Cannot lookup accessible no-arg constructor for: " + clazz.getName(), e);
}
}
private static final MethodHandles.Lookup lookup = MethodHandles.publicLookup();
private static final MethodType NO_ARG_CTOR = MethodType.methodType(void.class);
private static final MethodType NO_ARG_RETURNING_ATTRIBUTEIMPL = MethodType.methodType(AttributeImpl.class);
/**
* This is the default factory that creates {@link AttributeImpl}s using the
* class name of the supplied {@link Attribute} interface class by appending <code>Impl</code> to it.
*/
public static final AttributeFactory DEFAULT_ATTRIBUTE_FACTORY = new DefaultAttributeFactory(true);
static final class DefaultAttributeFactory extends AttributeFactory {
private final WeakIdentityMap<Class<? extends Attribute>, Object> attClassImplMap =
WeakIdentityMap.newConcurrentHashMap(false);
private final ClassLoader myClassLoader = getClass().getClassLoader();
private final boolean useMethodHandles;
// this constructor is available for tests, to be able to test the pure-reflective case, too
DefaultAttributeFactory(boolean useMethodHandles) {
this.useMethodHandles = useMethodHandles;
}
@Override
public AttributeImpl createAttributeInstance(Class<? extends Attribute> attClass) {
// first lookup from cache:
Object cached = attClassImplMap.get(attClass);
if (cached instanceof MethodHandle) {
return invokeMethodHandle((MethodHandle) cached);
} else if (cached instanceof Reference) {
@SuppressWarnings("unchecked") final Class<? extends AttributeImpl> clazz =
((Reference<Class<? extends AttributeImpl>>) cached).get();
if (clazz != null) {
return invokeReflective(clazz);
}
cached = null;
// fall-through
}
// No cache hit!
// Please note: we have the slight chance that another thread may do the same, but who cares?
assert cached == null;
final Class<? extends AttributeImpl> implClazz = findImplClass(attClass);
// if the attribute impl is from our own ClassLoader, we optimize to use pre-allocated MethodHandle to instantiate the object
if (useMethodHandles && implClazz.getClassLoader() == myClassLoader) {
final MethodHandle constr = findAttributeImplCtor(implClazz);
attClassImplMap.put(attClass, constr);
return invokeMethodHandle(constr);
} else {
// otherwise, to not refer to the class forever (because the MethodHandle strongly
// references the class), so it can never be unloaded, we use slower reflection:
attClassImplMap.put(attClass, new WeakReference<>(implClazz));
return invokeReflective(implClazz);
}
}
private Class<? extends AttributeImpl> findImplClass(Class<? extends Attribute> attClass) {
try {
return Class.forName(attClass.getName() + "Impl", true, attClass.getClassLoader()).asSubclass(AttributeImpl.class);
} catch (ClassNotFoundException cnfe) {
throw new IllegalArgumentException("Cannot find implementing class for: " + attClass.getName());
}
}
private AttributeImpl invokeMethodHandle(MethodHandle constr) {
try {
return (AttributeImpl) constr.invokeExact();
} catch (Throwable t) {
rethrow(t);
throw new AssertionError();
}
}
private AttributeImpl invokeReflective(Class<? extends AttributeImpl> implClass) {
try {
return implClass.newInstance();
} catch (InstantiationException | IllegalAccessException e) {
throw new IllegalArgumentException("Cannot instantiate implementing class: " + implClass.getName(), e);
}
}
}
/** <b>Expert</b>: AttributeFactory returning an instance of the given {@code clazz} for the
* attributes it implements. For all other attributes it calls the given delegate factory
* as fallback. This class can be used to prefer a specific {@code AttributeImpl} which
* combines multiple attributes over separate classes.
* @lucene.internal
*/
public abstract static class StaticImplementationAttributeFactory<A extends AttributeImpl> extends AttributeFactory {
private final AttributeFactory delegate;
private final Class<A> clazz;
/** <b>Expert</b>: Creates an AttributeFactory returning {@code clazz} as instance for the
* attributes it implements and for all other attributes calls the given delegate factory. */
public StaticImplementationAttributeFactory(AttributeFactory delegate, Class<A> clazz) {
this.delegate = delegate;
this.clazz = clazz;
}
@Override
public final AttributeImpl createAttributeInstance(Class<? extends Attribute> attClass) {
return attClass.isAssignableFrom(clazz) ? createInstance() : delegate.createAttributeInstance(attClass);
}
/** Creates an instance of {@code A}. */
protected abstract A createInstance();
@Override
public boolean equals(Object other) {
if (this == other)
return true;
if (other == null || other.getClass() != this.getClass())
return false;
@SuppressWarnings("rawtypes")
final StaticImplementationAttributeFactory af = (StaticImplementationAttributeFactory) other;
return this.delegate.equals(af.delegate) && this.clazz == af.clazz;
}
@Override
public int hashCode() {
return 31 * delegate.hashCode() + clazz.hashCode();
}
}
/** Returns an AttributeFactory returning an instance of the given {@code clazz} for the
* attributes it implements. The given {@code clazz} must have a public no-arg constructor.
* For all other attributes it calls the given delegate factory as fallback.
* This method can be used to prefer a specific {@code AttributeImpl} which combines
* multiple attributes over separate classes.
* <p>Please save instances created by this method in a static final field, because
* on each call, this does reflection for creating a {@link MethodHandle}.
*/
public static <A extends AttributeImpl> AttributeFactory getStaticImplementation(AttributeFactory delegate, Class<A> clazz) {
final MethodHandle constr = findAttributeImplCtor(clazz);
return new StaticImplementationAttributeFactory<A>(delegate, clazz) {
@Override
protected A createInstance() {
try {
return (A) constr.invokeExact();
} catch (Throwable t) {
rethrow(t);
throw new AssertionError();
}
}
};
}
// Hack to rethrow unknown Exceptions from {@link MethodHandle#invoke}:
// TODO: remove the impl in test-framework, this one is more elegant :-)
static void rethrow(Throwable t) {
AttributeFactory.<Error>rethrow0(t);
}
@SuppressWarnings("unchecked")
private static <T extends Throwable> void rethrow0(Throwable t) throws T {
throw (T) t;
}
}