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/**
* Copyright 2010 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.I0Itec.zkclient;
import java.io.Serializable;
import java.util.List;
import org.I0Itec.zkclient.exception.ZkNoNodeException;
public class DistributedQueue {
private static class Element {
private String _name;
private T _data;
public Element(String name, T data) {
_name = name;
_data = data;
}
public String getName() {
return _name;
}
public T getData() {
return _data;
}
}
private ZkClient _zkClient;
private String _root;
private static final String ELEMENT_NAME = "element";
public DistributedQueue(ZkClient zkClient, String root) {
_zkClient = zkClient;
_root = root;
}
public boolean offer(T element) {
try {
_zkClient.createPersistentSequential(_root + "/" + ELEMENT_NAME + "-", element);
} catch (Exception e) {
throw ExceptionUtil.convertToRuntimeException(e);
}
return true;
}
public T poll() {
while (true) {
Element element = getFirstElement();
if (element == null) {
return null;
}
try {
_zkClient.delete(element.getName());
return element.getData();
} catch (ZkNoNodeException e) {
// somebody else picked up the element first, so we have to
// retry with the new first element
} catch (Exception e) {
throw ExceptionUtil.convertToRuntimeException(e);
}
}
}
private String getSmallestElement(List list) {
String smallestElement = list.get(0);
for (String element : list) {
if (element.compareTo(smallestElement) < 0) {
smallestElement = element;
}
}
return smallestElement;
}
public boolean isEmpty() {
return _zkClient.getChildren(_root).size() == 0;
}
@SuppressWarnings("unchecked")
private Element getFirstElement() {
try {
while (true) {
List list = _zkClient.getChildren(_root);
if (list.size() == 0) {
return null;
}
String elementName = getSmallestElement(list);
try {
return new Element(_root + "/" + elementName, (T) _zkClient.readData(_root + "/" + elementName));
} catch (ZkNoNodeException e) {
// somebody else picked up the element first, so we have to
// retry with the new first element
}
}
} catch (Exception e) {
throw ExceptionUtil.convertToRuntimeException(e);
}
}
public T peek() {
Element element = getFirstElement();
if (element == null) {
return null;
}
return element.getData();
}
}