/*
* Copyright (c) 2010-2012 Grid Dynamics Consulting Services, Inc, All Rights Reserved
* http://www.griddynamics.com
*
* This library is free software; you can redistribute it and/or modify it under the terms of
* the Apache License; either
* version 2.0 of the License, or any later version.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package com.griddynamics.jagger.coordinator.zookeeper;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import static com.griddynamics.jagger.coordinator.zookeeper.Zoo.znode;
/**
* Lock implementation as described at {@see http://zookeeper.apache.org/doc/r3.1.2/recipes.html#sc_recipes_Locks}.
* <span color="#ff0000">In progress. May cause a deadlocks!</span>
*/
public class DefaultZNodeLock implements ZNodeLock {
private final ZNode node;
private final String lockPath;
private ZNode lockNode;
public DefaultZNodeLock(ZNode node) {
this(node, "lock");
}
public DefaultZNodeLock(ZNode node, String lockPath) {
this.node = node;
this.lockPath = lockPath;
}
private ZNode lockDir() {
return node.child(lockPath);
}
@Override
public void makeLockable() {
node.createChild(znode().withPath(lockPath));
}
@Override
public boolean isLockable() {
return node.hasChild(lockPath);
}
@Override
public void lock() {
while (true) {
ZNode node = lockDir().createChild(znode().ephemeralSequential());
final String currentNodeName = node.getShortPath();
int currentFlag = Integer.valueOf(currentNodeName);
final List<ZNode> children = lockDir().children();
int lowestNodeVal = Integer.MAX_VALUE;
int nextNodeFlag = -1;
String nextNodePath = null;
for (ZNode child : children) {
String childPath = child.getShortPath();
int childFlag = Integer.valueOf(childPath);
if (childFlag < lowestNodeVal) {
lowestNodeVal = childFlag;
}
if (childFlag < currentFlag && childFlag > nextNodeFlag) {
nextNodeFlag = childFlag;
nextNodePath = childPath;
}
}
if (currentFlag == lowestNodeVal) {
lockNode = node;
break;
}
final CountDownLatch signal = new CountDownLatch(1);
boolean hasChild = lockDir().hasChild(nextNodePath, new Watcher() {
@Override
public void process(WatchedEvent event) {
signal.countDown();
}
});
if (hasChild) {
lockNode = node;
try {
signal.await();
break;
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
}
node.remove();
}
}
@Override
public void unlock() {
if (lockNode == null) {
return;
}
lockNode.remove();
}
}