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Groovy: A powerful, dynamic language for the JVM
/**
* 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.
*/
package org.codehaus.groovy.util;
/**
* Soft reference with lazy initialization under lock
*/
public abstract class LazyReference extends LockableObject {
private static final ManagedReference INIT = new ManagedReference(ReferenceType.HARD,null,null){};
private static final ManagedReference NULL_REFERENCE = new ManagedReference(ReferenceType.HARD,null,null){};
private ManagedReference reference = INIT;
private final ReferenceBundle bundle;
public LazyReference(ReferenceBundle bundle) {
this.bundle = bundle;
}
public T get() {
ManagedReference resRef = reference;
if (resRef == INIT) return getLocked(false);
if (resRef == NULL_REFERENCE) return null;
T res = resRef.get();
// res== null means it got collected
if (res==null) return getLocked(true);
return res;
}
private T getLocked (boolean force) {
lock ();
try {
ManagedReference resRef = reference;
if (!force && resRef != INIT) return resRef.get();
T res = initValue();
if (res == null) {
reference = NULL_REFERENCE;
} else {
reference = new ManagedReference(bundle,res);
}
return res;
} finally {
unlock();
}
}
public void clear() {
reference = INIT;
}
public abstract T initValue();
public String toString() {
T res = reference.get();
if (res == null)
return "";
else
return res.toString();
}
}