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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.util;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
/** This class provides something of a cyclic version of a CountDownLatch.
*
* The latch resets when await() completes. It may ignore calls to countDown()
* that occur before await() returns (it is not accumulative).
*
* Use this class with caution.
*/
public class CyclicCountDownLatch {
private static class Sync extends AbstractQueuedSynchronizer {
final int count;
public Sync(int count) {
this.count = count;
setState(count);
}
@Override protected boolean tryReleaseShared(int unused) {
boolean success = false;
while (!success) {
int expect = getState();
int update = Math.max(expect - 1, 0);
success = compareAndSetState(expect, update);
}
return getState() <= 0;
}
@Override protected int tryAcquireShared(int unused) {
boolean success = false;
while (!success) {
int expect = getState();
if (expect > 0) {
break;
}
int update = count;
success = compareAndSetState(expect, update);
}
if (success) {
// Non-exclusive success. Other threads may attempt to acquire.
return 1;
} else {
// Failure.
return -1;
}
}
public int getCount() {
return getState();
}
}
private final Sync sync;
public CyclicCountDownLatch(int count) {
sync = new Sync(count);
}
public void await() throws InterruptedException {
sync.acquireSharedInterruptibly(-1);
}
public void countDown() {
sync.releaseShared(-1);
}
public int getCount() {
return sync.getCount();
}
}
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