001/*
002 * ModeShape (http://www.modeshape.org)
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *       http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.modeshape.common.collection.ring;
018
019import java.util.concurrent.locks.Condition;
020import java.util.concurrent.locks.Lock;
021import java.util.concurrent.locks.ReentrantLock;
022
023/**
024 * A {@link WaitStrategy} that blocks the current thread until an entry is available for consumption. This implementation uses
025 * Java locks and {@link Condition conditions}.
026 * 
027 * @author Randall Hauch (rhauch@redhat.com)
028 */
029public class BlockingWaitStrategy implements WaitStrategy {
030
031    private final Lock lock = new ReentrantLock();
032    private final Condition waitCondition = lock.newCondition();
033
034    @Override
035    public long waitFor( long position,
036                         Pointer pointer,
037                         Pointer dependentPointer,
038                         PointerBarrier barrier ) throws InterruptedException {
039        // Get the next position that is immediately available ...
040        long availablePosition = pointer.get();
041        if (availablePosition < position) {
042            // The caller wants a position that is farther along than what is available, so we have to block ...
043            lock.lock();
044            try {
045                while (!barrier.isComplete() && (availablePosition = pointer.get()) < position) {
046                    waitCondition.await();
047                }
048            } finally {
049                lock.unlock();
050            }
051        }
052        return availablePosition;
053    }
054
055    @Override
056    public void signalAllWhenBlocking() {
057        lock.lock();
058        try {
059            waitCondition.signalAll();
060        } finally {
061            lock.unlock();
062        }
063    }
064}