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/**
* Copyright 2012 Kjetil Ørbekk <kjetil.orbekk@gmail.com>
*
* Licensed 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 com.orbekk.same;
import java.util.concurrent.atomic.AtomicBoolean;
/** Updates a variable on-demand.
*/
public class VariableUpdaterTask<T> extends Thread
implements Variable.OnChangeListener<T> {
private Variable<T> variable;
private volatile T newValue;
private AtomicBoolean hasNewValue = new AtomicBoolean(false);
private AtomicBoolean isReady = new AtomicBoolean(true);
public VariableUpdaterTask(Variable<T> variable) {
super("VariableUpdater");
this.variable = variable;
}
public synchronized void set(T newValue) {
this.newValue = newValue;
hasNewValue.set(true);
notifyAll();
}
/** Update the variable once. */
public void performWork() {
boolean shouldDoWork = false;
synchronized(this) {
shouldDoWork = hasNewValue.get() && isReady.get();
hasNewValue.set(false);
isReady.set(false);
}
if (shouldDoWork) {
variable.set(newValue);
}
}
private synchronized void waitFor(AtomicBoolean v) {
if (Thread.currentThread().isInterrupted()) {
return;
}
while(!v.get()) {
try {
wait();
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
return;
}
}
}
@Override
public void run() {
variable.addOnChangeListener(this);
while (true) {
waitFor(isReady);
waitFor(hasNewValue);
if (Thread.currentThread().isInterrupted()) {
break;
}
performWork();
}
variable.removeOnChangeListener(this);
}
@Override
public synchronized void valueChanged(Variable<T> unused) {
isReady.set(true);
notifyAll();
}
}
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