LeaderElectionService.java

/**
 * Copyright 2016 vip.com.
 * <p>
 * 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.
 * </p>
 */

package com.vip.saturn.job.internal.election;

import java.util.concurrent.atomic.AtomicBoolean;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.vip.saturn.job.basic.AbstractSaturnService;
import com.vip.saturn.job.basic.JobScheduler;
import com.vip.saturn.job.basic.SaturnConstant;
import com.vip.saturn.job.internal.storage.LeaderExecutionCallback;
import com.vip.saturn.job.utils.BlockUtils;

/**
 * 选举主节点的服务.
 * 
 * 
 */
public class LeaderElectionService extends AbstractSaturnService{
	static Logger log = LoggerFactory.getLogger(LeaderElectionService.class);

    private AtomicBoolean isShutdown = new AtomicBoolean(false);
    
    public LeaderElectionService(final JobScheduler jobScheduler) {
    	super(jobScheduler);
    }


    @Override
    public void shutdown() {
        synchronized (isShutdown) {
            if(isShutdown.compareAndSet(false, true)) {
                try { // Release my leader position
                    if (executorName.equals(getJobNodeStorage().getJobNodeDataDirectly(ElectionNode.LEADER_HOST))) {
                        getJobNodeStorage().removeJobNodeIfExisted(ElectionNode.LEADER_HOST);
                        log.info("[{}] msg={} that was {}'s leader, released itself", jobName, executorName, jobName);
                    }
                } catch (Throwable t) {
                    log.error(t.getMessage(), t);
                }
            }
        }
    }
    
    /**
     * 选举主节点.
     */
    public void leaderElection() {
        getJobNodeStorage().executeInLeader(ElectionNode.LATCH, new LeaderElectionExecutionCallback());
    }
    
    /**
     * 判断当前节点是否是主节点，如果没有主节点，则选举，直到有主节点
     *
     * @return 当前节点是否是主节点
     */
    public Boolean isLeader() {
        while (!isShutdown.get() && !hasLeader()) {
            log.info("[{}] msg=No leader, try to election", jobName);
            leaderElection();
        }
        return executorName.equals(getJobNodeStorage().getJobNodeDataDirectly(ElectionNode.LEADER_HOST));
    }
    
    /**
     * 判断是否已经有主节点
     * 
     * @return 是否已经有主节点
     */
    public boolean hasLeader() {
        return getJobNodeStorage().isJobNodeExisted(ElectionNode.LEADER_HOST);
    }
    
    class LeaderElectionExecutionCallback implements LeaderExecutionCallback {
        
        @Override
        public void execute() {
            synchronized (isShutdown) {
                if(isShutdown.get()) {
                    return;
                }
                if (!getJobNodeStorage().isJobNodeExisted(ElectionNode.LEADER_HOST)) {
                    getJobNodeStorage().fillEphemeralJobNode(ElectionNode.LEADER_HOST, executorName);
                    log.info("[{}] msg=executor {} become job {}'s leader", jobName, executorName, jobName);
                }
            }
        }
    }
}