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 }