org.opencastproject.util.data.Cells Maven / Gradle / Ivy
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* Licensed to The Apereo Foundation under one or more contributor license
* agreements. See the NOTICE file distributed with this work for additional
* information regarding copyright ownership.
*
*
* The Apereo Foundation licenses this file to you under the Educational
* Community 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://opensource.org/licenses/ecl2.txt
*
* 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.
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*/
package org.opencastproject.util.data;
import static org.opencastproject.util.EqualsUtil.ne;
import static org.opencastproject.util.data.Tuple.tuple;
public final class Cells {
private Cells() {
}
abstract static class FCell extends Cell {
protected A a;
protected Object change = new Object();
protected final Object lock = new Object();
protected abstract A calc();
@Override public A get() {
synchronized (lock) {
return calc();
}
}
@Override protected Tuple change() {
synchronized (lock) {
return tuple(calc(), change);
}
}
}
public static Cell fcell(final Cell master, final Function f) {
return new FCell() {
@Override protected A calc() {
final Tuple mChange = master.change();
if (ne(mChange.getB(), change)) {
a = f.apply(mChange.getA());
change = mChange.getB();
}
return a;
}
};
}
}