001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.camel.util.concurrent;
018    
019    import java.util.concurrent.TimeUnit;
020    import java.util.concurrent.locks.AbstractQueuedSynchronizer;
021    
022    /**
023     * An alternative to a {@link java.util.concurrent.CountDownLatch}.
024     * <p/>
025     * This implementation also supports incrementing the latch count while counting down.
026     * It can also be used to count up to 0 from a negative integer.
027     */
028    public class CountingLatch {
029    
030        @SuppressWarnings("serial")
031        private final class Sync extends AbstractQueuedSynchronizer {
032    
033            private Sync() {
034                super();
035            }
036    
037            int getCount() {
038                return getState();
039            }
040    
041            public int tryAcquireShared(int acquires) {
042                return getState() == 0 ? 1 : -1;
043            }
044    
045            public boolean tryReleaseShared(int delta) {
046                // Decrement count; signal when transition to zero
047                for (;;) {
048                    int c = getState();
049                    int nextc = c + delta;
050                    if (compareAndSetState(c, nextc)) {
051                        return nextc == 0;
052                    }
053                }
054            }
055        }
056    
057        private final Sync sync;
058    
059        /**
060         * Create a new counting latch (starting count is 0)
061         */
062        public CountingLatch() {
063            super();
064            this.sync = new Sync();
065        }
066    
067        /**
068         * Get the current count
069         */
070        public int getCount() {
071            return sync.getCount();
072        }
073    
074        /**
075         * Increment the count with 1
076         */
077        public void increment() {
078            sync.releaseShared(+1);
079        }
080    
081        /**
082         * Decrement the count with 1
083         */
084        public void decrement() {
085            sync.releaseShared(-1);
086        }
087    
088        /**
089         * Await the latch reaching the count of 0
090         *
091         * @throws InterruptedException if the threads gets interrupted while waiting
092         */
093        public void await() throws InterruptedException {
094            sync.acquireSharedInterruptibly(1);
095        }
096    
097        /**
098         * Wait for a given timeout while checking if the latch reached the count of 0
099         *
100         * @param timeout the value of the timeout
101         * @param unit the unit in which the timeout is expressed
102         * @return <code>true</code> if the latch has reached the count of 0 in the given time
103         * @throws InterruptedException if the thread gets interrupted while waiting
104         */
105        public boolean await(long timeout, TimeUnit unit) throws InterruptedException {
106            return sync.tryAcquireSharedNanos(1, unit.toNanos(timeout));
107        }
108    
109    }