103 lines
4.1 KiB
Java
103 lines
4.1 KiB
Java
/*
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* Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package jdk.internal.loader;
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import java.util.Objects;
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import java.util.function.BiFunction;
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/**
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* root-ClassLoaderValue. Each instance defines a separate namespace for
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* associated values.
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* <p>
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* ClassLoaderValue allows associating a
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* {@link #computeIfAbsent(ClassLoader, BiFunction) computed} non-null value with
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* a {@code (ClassLoader, keys...)} tuple. The associated value, as well as the
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* keys are strongly reachable from the associated ClassLoader so care should be
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* taken to use such keys and values that only reference types resolvable from
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* the associated ClassLoader. Failing that, ClassLoader leaks are inevitable.
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* <p>
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* Example usage:
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* <pre>{@code
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* // create a root instance which represents a namespace and declares the type of
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* // associated values (Class instances in this example)
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* static final ClassLoaderValue<Class<?>> proxyClasses = new ClassLoaderValue<>();
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*
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* // create a compound key composed of a Module and a list of interfaces
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* Module module = ...;
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* List<Class<?>> interfaces = ...;
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* ClassLoaderValue<Class<?>>.Sub<Module>.Sub<List<Class<?>>> key =
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* proxyClasses.sub(module).sub(interfaces);
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*
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* // use the compound key together with ClassLoader to lazily associate
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* // the value with tuple (loader, module, interfaces) and return it
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* ClassLoader loader = ...;
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* Class<?> proxyClass = key.computeIfAbsent(loader, (ld, ky) -> {
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* List<Class<?>> intfcs = ky.key();
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* Module m = ky.parent().key();
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* Class<?> clazz = defineProxyClass(ld, m, intfcs);
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* return clazz;
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* });
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* }</pre>
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* <p>
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* {@code classLoaderValue.<operation>(classLoader, ...)} represents an operation
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* to {@link #get}, {@link #putIfAbsent}, {@link #computeIfAbsent} or {@link #remove}
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* a value associated with a (classLoader, classLoaderValue) tuple. ClassLoader
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* instances and root-{@link ClassLoaderValue} instances are compared using
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* identity equality while {@link Sub sub}-ClassLoaderValue instances define
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* {@link #equals(Object) equality} in terms of equality of its
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* {@link Sub#parent() parent} ClassLoaderValue and its
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* {@link #key() key} component.
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*
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* @param <V> the type of value(s) associated with the root-ClassLoaderValue and
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* all its {@link #sub(Object) descendants}.
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* @author Peter Levart
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* @since 9
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*/
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public final class ClassLoaderValue<V>
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extends AbstractClassLoaderValue<ClassLoaderValue<V>, V> {
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/**
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* Constructs new root-ClassLoaderValue representing its own namespace.
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*/
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public ClassLoaderValue() {}
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/**
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* @return the key component of this root-ClassLoaderValue (itself).
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*/
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@Override
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public ClassLoaderValue<V> key() {
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return this;
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}
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/**
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* root-ClassLoaderValue can only be equal to itself and has no predecessors.
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*/
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@Override
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public boolean isEqualOrDescendantOf(AbstractClassLoaderValue<?, V> clv) {
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return equals(Objects.requireNonNull(clv));
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}
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}
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