MasterQueue.java

/**
 * Copyright 2008 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 net.sf.katta.protocol;

import java.util.ArrayList;
import java.util.List;

import net.sf.katta.master.OperationWatchdog;
import net.sf.katta.operation.OperationId;
import net.sf.katta.operation.master.MasterOperation;

import org.I0Itec.zkclient.ZkClient;
import org.I0Itec.zkclient.exception.ZkNoNodeException;

public class MasterQueue extends BlockingQueue<MasterOperation> {

  private String _watchdogsPath;

  public MasterQueue(ZkClient zkClient, String rootPath) {
    super(zkClient, rootPath);
    _watchdogsPath = rootPath + "/watchdogs";
    _zkClient.createPersistent(_watchdogsPath, true);

    // cleanup odd watchdog situations
    List<String> watchdogs = _zkClient.getChildren(_watchdogsPath);
    for (String elementName : watchdogs) {
      try {
        _zkClient.delete(getElementPath(elementName));
      } catch (ZkNoNodeException e) {
        // ignore, can be already deleted by other queue instance
      }
    }
  }

  private String getWatchdogPath(String elementId) {
    return _watchdogsPath + "/" + elementId;
  }

  /**
   * Moves the top of the queue to the watching state.
   * 
   * @param masterOperation
   * @param nodeOperationIds
   * @return
   * @throws InterruptedException
   */
  public OperationWatchdog moveOperationToWatching(MasterOperation masterOperation, List<OperationId> nodeOperationIds)
          throws InterruptedException {
    Element<MasterOperation> element = getFirstElement();
    // we don't use the persisted operation cause the given masterOperation can
    // have a changed state
    OperationWatchdog watchdog = new OperationWatchdog(element.getName(), masterOperation, nodeOperationIds);
    _zkClient.createPersistent(getWatchdogPath(element.getName()), watchdog);
    _zkClient.delete(getElementPath(element.getName()));
    return watchdog;
  }

  public List<OperationWatchdog> getWatchdogs() {
    List<String> childs = _zkClient.getChildren(_watchdogsPath);
    List<OperationWatchdog> watchdogs = new ArrayList<OperationWatchdog>(childs.size());
    for (String child : childs) {
      watchdogs.add((OperationWatchdog) _zkClient.readData(getWatchdogPath(child)));
    }
    return watchdogs;
  }

  public void removeWatchdog(OperationWatchdog watchdog) {
    _zkClient.delete(getWatchdogPath(watchdog.getQueueElementId()));
  }

}