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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.AtomicReference;
import java.util.logging.Logger;
import com.orbekk.util.CyclicCountDownLatch;
import com.orbekk.util.DelayedOperation;
/** Updates a variable on-demand.
*/
public class VariableUpdaterTask<T> extends Thread
implements Variable.OnChangeListener<T> {
private static Logger logger = Logger.getLogger(VariableUpdaterTask.class.getName());
private Variable<T> variable;
private AtomicReference<T> newValue = new AtomicReference<T>();
private CyclicCountDownLatch hasNewValue = new CyclicCountDownLatch(1);
private CyclicCountDownLatch isReady = new CyclicCountDownLatch(1);
public VariableUpdaterTask(Variable<T> variable) {
super("VariableUpdater");
this.variable = variable;
}
public void set(T newValue) {
this.newValue.set(newValue);
hasNewValue.countDown();
}
void setValue(T newValue) {
while (!Thread.currentThread().isInterrupted()) {
DelayedOperation op = variable.set(newValue);
if (op.getStatus().isOk()) {
return;
} else if (op.getStatus().isConflict()) {
// We have a new value, but we need to wait for an update
// in order to overwrite it.
hasNewValue.countDown();
return;
} else if (op.getStatus().isError()) {
// Error during update. Just retry.
logger.info("Error updating value. Status: " + op.getStatus());
} else {
throw new AssertionError("Unknown state.");
}
}
}
@Override
public void valueChanged(Variable<T> variable) {
isReady.countDown();
variable.update();
}
@Override
public void run() {
isReady.countDown(); // Initially ready.
variable.addOnChangeListener(this);
while (!Thread.interrupted()) {
try {
hasNewValue.await();
isReady.await();
setValue(newValue.get());
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
}
logger.info("VariableUpdaterTask finished.");
}
}
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