/*
* 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.
*
* 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.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 computed non-null value with a (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:
// create a root instance which represents a namespace and declares the type of
// associated values (Class instances in this example)
static final ClassLoaderValue<Class<?>> proxyClasses = new ClassLoaderValue<>();
// create a compound key composed of a Module and a list of interfaces
Module module = ...;
List<Class<?>> interfaces = ...;
ClassLoaderValue<Class<?>>.Sub<Module>.Sub<List<Class<?>>> 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<Class<?>> intfcs = ky.key();
Module m = ky.parent().key();
Class<?> clazz = defineProxyClass(ld, m, intfcs);
return clazz;
});
classLoaderValue.<operation>(classLoader, ...) represents an operation to AbstractClassLoaderValue.get, AbstractClassLoaderValue.putIfAbsent, AbstractClassLoaderValue.computeIfAbsent or AbstractClassLoaderValue.remove a value associated with a (classLoader, classLoaderValue) tuple. ClassLoader instances and root-ClassLoaderValue instances are compared using identity equality while sub-ClassLoaderValue instances define equality in terms of equality of its parent ClassLoaderValue and its key component.
Author: Peter Levart Type parameters: - <V> – the type of value(s) associated with the root-ClassLoaderValue and all its
descendants.
Since: 9
/**
* root-ClassLoaderValue. Each instance defines a separate namespace for
* associated values.
* <p>
* 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.
* <p>
* Example usage:
* <pre>{@code
* // create a root instance which represents a namespace and declares the type of
* // associated values (Class instances in this example)
* static final ClassLoaderValue<Class<?>> proxyClasses = new ClassLoaderValue<>();
*
* // create a compound key composed of a Module and a list of interfaces
* Module module = ...;
* List<Class<?>> interfaces = ...;
* ClassLoaderValue<Class<?>>.Sub<Module>.Sub<List<Class<?>>> 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<Class<?>> intfcs = ky.key();
* Module m = ky.parent().key();
* Class<?> clazz = defineProxyClass(ld, m, intfcs);
* return clazz;
* });
* }</pre>
* <p>
* {@code classLoaderValue.<operation>(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 <V> 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<V>
extends AbstractClassLoaderValue<ClassLoaderValue<V>, V> {
Constructs new root-ClassLoaderValue representing its own namespace.
/**
* Constructs new root-ClassLoaderValue representing its own namespace.
*/
public ClassLoaderValue() {}
Returns: the key component of this root-ClassLoaderValue (itself).
/**
* @return the key component of this root-ClassLoaderValue (itself).
*/
@Override
public ClassLoaderValue<V> key() {
return this;
}
root-ClassLoaderValue can only be equal to itself and has no predecessors.
/**
* root-ClassLoaderValue can only be equal to itself and has no predecessors.
*/
@Override
public boolean isEqualOrDescendantOf(AbstractClassLoaderValue<?, V> clv) {
return equals(Objects.requireNonNull(clv));
}
}