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.CountDownLatch;
020    import java.util.concurrent.TimeUnit;
021    import java.util.concurrent.locks.AbstractQueuedSynchronizer;
022    
023    /**
024     * An alternative to a {@link CountDownLatch} -- this implementation also supports incrementing
025     * the latch count while counting down.  It can also be used to count up to 0 from a negative integer.
026     */
027    public class CountingLatch {
028    
029        @SuppressWarnings("serial")
030        private final class Sync extends AbstractQueuedSynchronizer {
031    
032            private Sync() {
033                super();
034            }
035    
036            int getCount() {
037                return getState();
038            }
039    
040            public int tryAcquireShared(int acquires) {
041                return getState() == 0 ? 1 : -1;
042            }
043    
044            public boolean tryReleaseShared(int delta) {
045                // Decrement count; signal when transition to zero
046                for (;;) {
047                    int c = getState();
048                    int nextc = c + delta;
049                    if (compareAndSetState(c, nextc)) {
050                        return nextc == 0;
051                    }
052                }
053            }
054        }
055    
056        private final Sync sync;
057    
058        /**
059         * Create a new counting latch (starting count is 0)
060         */
061        public CountingLatch() {
062            super();
063            this.sync = new Sync();
064        }
065    
066        /**
067         * Get the current count
068         */
069        public int getCount() {
070            return sync.getCount();
071        }
072    
073        /**
074         * Increment the count with 1
075         */
076        public void increment() {
077            sync.releaseShared(+1);
078        }
079    
080        /**
081         * Decrement the count with 1
082         */
083        public void decrement() {
084            sync.releaseShared(-1);
085        }
086    
087        /**
088         * Await the latch reaching the count of 0
089         *
090         * @throws InterruptedException if the threads gets interrupted while waiting
091         */
092        public void await() throws InterruptedException {
093            sync.acquireSharedInterruptibly(1);
094        }
095    
096        /**
097         * Wait for a given timeout while checking if the latch reached the count of 0
098         *
099         * @param timeout the value of the timeout
100         * @param unit the unit in which the timeout is expressed
101         * @return <code>true</code> if the latch has reached the count of 0 in the given time
102         * @throws InterruptedException if the thread gets interrupted while waiting
103         */
104        public boolean await(long timeout, TimeUnit unit) throws InterruptedException {
105            return sync.tryAcquireSharedNanos(1, unit.toNanos(timeout));
106        }
107    
108    }