org.elasticsearch.common.util.concurrent.CountDown Maven / Gradle / Ivy

Go to download
/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */

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 true iff this call
     * reached zero otherwise false
     */
    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 true iff
     * the count down reached zero with this fast forward call otherwise
     * false
     */
    public boolean fastForward() {
        assert originalCount > 0;
        assert countDown.get() >= 0;
        return countDown.getAndSet(0) > 0;
    }

    /**
     * Returns true iff the count-down has reached zero. Otherwise false
     */
    public boolean isCountedDown() {
        assert countDown.get() >= 0;
        return countDown.get() == 0;
    }
}