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/*
* Copyright (c) 2016, 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.
*
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package jdk.internal.loader;
import java.util.Objects;
import java.util.function.BiFunction;
/**
* root-ClassLoaderValue. Each instance defines a separate namespace for
* associated values.
*
* ClassLoaderValue allows associating a
* {@link #computeIfAbsent(ClassLoader, BiFunction) computed} non-null value with
* a {@code (ClassLoader, keys...)} tuple. The associated value, as well as the
* keys are strongly reachable from the associated ClassLoader so care should be
* taken to use such keys and values that only reference types resolvable from
* the associated ClassLoader. Failing that, ClassLoader leaks are inevitable.
*
* Example usage:
*
{@code
* // create a root instance which represents a namespace and declares the type of
* // associated values (Class instances in this example)
* static final ClassLoaderValue> proxyClasses = new ClassLoaderValue<>();
*
* // create a compound key composed of a Module and a list of interfaces
* Module module = ...;
* List> interfaces = ...;
* ClassLoaderValue>.Sub.Sub>> key =
* proxyClasses.sub(module).sub(interfaces);
*
* // use the compound key together with ClassLoader to lazily associate
* // the value with tuple (loader, module, interfaces) and return it
* ClassLoader loader = ...;
* Class proxyClass = key.computeIfAbsent(loader, (ld, ky) -> {
* List> intfcs = ky.key();
* Module m = ky.parent().key();
* Class clazz = defineProxyClass(ld, m, intfcs);
* return clazz;
* });
* }
*
* {@code classLoaderValue.(classLoader, ...)} represents an operation
* to {@link #get}, {@link #putIfAbsent}, {@link #computeIfAbsent} or {@link #remove}
* a value associated with a (classLoader, classLoaderValue) tuple. ClassLoader
* instances and root-{@link ClassLoaderValue} instances are compared using
* identity equality while {@link Sub sub}-ClassLoaderValue instances define
* {@link #equals(Object) equality} in terms of equality of its
* {@link Sub#parent() parent} ClassLoaderValue and its
* {@link #key() key} component.
*
* @param the type of value(s) associated with the root-ClassLoaderValue and
* all its {@link #sub(Object) descendants}.
* @author Peter Levart
* @since 9
*/
public final class ClassLoaderValue
extends AbstractClassLoaderValue, V> {
/**
* Constructs new root-ClassLoaderValue representing its own namespace.
*/
public ClassLoaderValue() {}
/**
* @return the key component of this root-ClassLoaderValue (itself).
*/
@Override
public ClassLoaderValue key() {
return this;
}
/**
* root-ClassLoaderValue can only be equal to itself and has no predecessors.
*/
@Override
public boolean isEqualOrDescendantOf(AbstractClassLoaderValue clv) {
return equals(Objects.requireNonNull(clv));
}
}