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/*
Copyright 2009-2013 Attila Szegedi
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:
* Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
* Neither the name of the copyright holder nor the names of
contributors may be used to endorse or promote products derived from
this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL COPYRIGHT HOLDER
BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package jdk.dynalink;
import java.lang.ref.Reference;
import java.lang.ref.SoftReference;
import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import jdk.dynalink.internal.AccessControlContextFactory;
import jdk.dynalink.internal.InternalTypeUtilities;
A dual map that can either strongly or weakly reference a given class depending on whether the class is visible from
a class loader or not.
Type parameters: - <T> – the type of the values in the map
/**
* A dual map that can either strongly or weakly reference a given class depending on whether the class is visible from
* a class loader or not.
*
* @param <T> the type of the values in the map
*/
abstract class ClassMap<T> {
private static final AccessControlContext GET_CLASS_LOADER_CONTEXT =
AccessControlContextFactory.createAccessControlContext("getClassLoader");
private final ConcurrentMap<Class<?>, T> map = new ConcurrentHashMap<>();
private final Map<Class<?>, Reference<T>> weakMap = new WeakHashMap<>();
private final ClassLoader classLoader;
Creates a new class map. It will use strong references for all keys and values where the key is a class visible
from the class loader, and will use weak keys and soft values for all other classes.
Params: - classLoader – the classloader that determines strong referenceability.
/**
* Creates a new class map. It will use strong references for all keys and values where the key is a class visible
* from the class loader, and will use weak keys and soft values for all other classes.
*
* @param classLoader the classloader that determines strong referenceability.
*/
ClassMap(final ClassLoader classLoader) {
this.classLoader = classLoader;
}
Compute the value associated with the given class. It is possible that the method will be invoked several times
(or even concurrently) for the same class parameter.
Params: - clazz – the class to compute the value for
Returns: the return value. Must not be null.
/**
* Compute the value associated with the given class. It is possible that the method will be invoked several times
* (or even concurrently) for the same class parameter.
*
* @param clazz the class to compute the value for
* @return the return value. Must not be null.
*/
abstract T computeValue(Class<?> clazz);
Returns the value associated with the class
Params: - clazz – the class
Returns: the value associated with the class
/**
* Returns the value associated with the class
*
* @param clazz the class
* @return the value associated with the class
*/
T get(final Class<?> clazz) {
// Check in fastest first - objects we're allowed to strongly reference
final T v = map.get(clazz);
if(v != null) {
return v;
}
// Check objects we're not allowed to strongly reference
Reference<T> ref;
synchronized(weakMap) {
ref = weakMap.get(clazz);
}
if(ref != null) {
final T refv = ref.get();
if(refv != null) {
return refv;
}
}
// Not found in either place; create a new value
final T newV = computeValue(clazz);
assert newV != null;
final Boolean canReferenceDirectly = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
@Override
public Boolean run() {
return InternalTypeUtilities.canReferenceDirectly(classLoader, clazz.getClassLoader());
}
}, GET_CLASS_LOADER_CONTEXT);
// If allowed to strongly reference, put it in the fast map
if(canReferenceDirectly) {
final T oldV = map.putIfAbsent(clazz, newV);
return oldV != null ? oldV : newV;
}
// Otherwise, put it into the weak map
synchronized(weakMap) {
ref = weakMap.get(clazz);
if(ref != null) {
final T oldV = ref.get();
if(oldV != null) {
return oldV;
}
}
weakMap.put(clazz, new SoftReference<>(newV));
return newV;
}
}
}