/*
* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch 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.elasticsearch.common.util.concurrent;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.atomic.AtomicInteger;
/**
* A simple thread safe count-down class that in contrast to a {@link CountDownLatch}
* never blocks. This class is useful if a certain action has to wait for N concurrent
* tasks to return or a timeout to occur in order to proceed.
*/
public final class CountDown {
private final AtomicInteger countDown;
private final int originalCount;
public CountDown(int count) {
if (count < 0) {
throw new IllegalArgumentException("count must be greater or equal to 0 but was: " + count);
}
this.originalCount = count;
this.countDown = new AtomicInteger(count);
}
/**
* Decrements the count-down and returns <code>true</code> iff this call
* reached zero otherwise <code>false</code>
*/
public boolean countDown() {
assert originalCount > 0;
for (;;) {
final int current = countDown.get();
assert current >= 0;
if (current == 0) {
return false;
}
if (countDown.compareAndSet(current, current - 1)) {
return current == 1;
}
}
}
/**
* Fast forwards the count-down to zero and returns <code>true</code> iff
* the count down reached zero with this fast forward call otherwise
* <code>false</code>
*/
public boolean fastForward() {
assert originalCount > 0;
assert countDown.get() >= 0;
return countDown.getAndSet(0) > 0;
}
/**
* Returns <code>true</code> iff the count-down has reached zero. Otherwise <code>false</code>
*/
public boolean isCountedDown() {
assert countDown.get() >= 0;
return countDown.get() == 0;
}
}