CountingLatch.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF 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.apache.openejb.util;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;

/**
 * @version $Rev$ $Date$
 */
public class CountingLatch {

    private final Sync sync;

    public CountingLatch() {
        this(0);
    }

    public CountingLatch(final int count) {
        this.sync = new Sync(count);
    }

    public void await() throws InterruptedException {
        sync.acquireSharedInterruptibly(1);
    }

    public boolean await(final long timeout, final TimeUnit unit) throws InterruptedException {
        return sync.tryAcquireSharedNanos(1, unit.toNanos(timeout));
    }

    public void countDown() {
        sync.releaseShared(-1);
    }

    public void countUp() {
        sync.releaseShared(1);
    }

    public long getCount() {
        return sync.getCount();
    }

    private static final class Sync extends AbstractQueuedSynchronizer {
        private Sync(final int count) {
            setState(count);
        }

        public boolean tryReleaseShared(final int releases) {
            while (true) {
                final int count = getState();

                final int next = count + releases;

                if (next < 0) {
                    return false;
                }

                if (compareAndSetState(count, next)) {
                    return next == 0;
                }
            }
        }

        public int tryAcquireShared(final int acquires) {
            return getState() == 0 ? 1 : -1;
        }

        int getCount() {
            return getState();
        }
    }
}