Elastic-Job源码分析之AbstractElasticJobExecutor分析

还记得我们在JobScheduler中，在创建任务详情时，会调用一个建造器JobBuilder来创建一个Job，类型是LiteJob。

LiteJob.java

/**
 * Lite调度作业.
 *
 * @author zhangliang
 */
public final class LiteJob implements Job {
    
    @Setter
    private ElasticJob elasticJob;
    
    @Setter
    private JobFacade jobFacade;
    
    @Override
    public void execute(final JobExecutionContext context) throws JobExecutionException {
        JobExecutorFactory.getJobExecutor(elasticJob, jobFacade).execute();
    }
}

进入到LiteJob，我们可以看到，它继承自quartz中的Job，同时新增了两个属性elasticJob和jobFacade，这个我们后续分析。我们关注的是execute方法。首先通过工厂模式，确定了执行器，我们可以看到有三种执行器，分别是ScriptJobExecutor、SimpleJobExecutor和DataflowJobExecutor，分别对应了三种job类型。由于SimpleJob覆盖了80%的使用场景，我们主要来分析一下SimpleJobExecutor。

SimpleExecutor.java

public final class SimpleJobExecutor extends AbstractElasticJobExecutor {
    
    private final SimpleJob simpleJob;
    
    public SimpleJobExecutor(final SimpleJob simpleJob, final JobFacade jobFacade) {
        super(jobFacade);
        this.simpleJob = simpleJob;
    }
    
    @Override
    protected void process(final ShardingContext shardingContext) {
        simpleJob.execute(shardingContext);
    }
}

这个执行器继承自AbstractElasticJobExecutor，然后里面实现的内容也很简单，子类需要实现父类的方法process，其他的方法在父类中执行。我们重点看一下AbstractElasticJobExecutor这个基础执行器。

AbstractElasticJobExecutor.java

从代码结构看，主要看几个方法，execute()和process()，这边都是前后依赖的，所以我们顺序看一下。

execute()

try {
    jobFacade.checkJobExecutionEnvironment();
} catch (final JobExecutionEnvironmentException cause) {
    jobExceptionHandler.handleException(jobName, cause);
}

首先检查运行环境信息。跟进去，我们可以发现，检查的内容是本机与注册中心的时间误差秒数是否在允许范围，就是我们配置的max-time-diff-seconds，超过范围就直接抛出异常。

ShardingContexts shardingContexts = jobFacade.getShardingContexts();
if (shardingContexts.isAllowSendJobEvent()) {
    jobFacade.postJobStatusTraceEvent(shardingContexts.getTaskId(), State.TASK_STAGING, String.format("Job '%s' execute begin.", jobName));
}

接着，首先获取分片上下文信息。获取分片上下文的具体执行内容为：

@Override
public ShardingContexts getShardingContexts() {
    boolean isFailover = configService.load(true).isFailover();
    if (isFailover) {
        List<Integer> failoverShardingItems = failoverService.getLocalFailoverItems();
        if (!failoverShardingItems.isEmpty()) {
            return executionContextService.getJobShardingContext(failoverShardingItems);
        }
    }
    shardingService.shardingIfNecessary();
    List<Integer> shardingItems = shardingService.getLocalShardingItems();
    if (isFailover) {
        shardingItems.removeAll(failoverService.getLocalTakeOffItems());
    }
    shardingItems.removeAll(executionService.getDisabledItems(shardingItems));
    return executionContextService.getJobShardingContext(shardingItems);
}

首先根据配置判断是否开启失效转移failover，开启表示如果作业在一次任务执行中途宕机，允许将该次未完成的任务在另一作业节点上补偿执行。

下一步，判断是否需要分片。

public void shardingIfNecessary() {
    List<JobInstance> availableJobInstances = instanceService.getAvailableJobInstances();//获取可用任务节点
    if (!isNeedSharding() || availableJobInstances.isEmpty()) {
        return;
    }
    if (!leaderService.isLeaderUntilBlock()) {//判断当前节点是否是主节点，如果主节点正在选举，则阻塞至主节点选举完成后再返回
        blockUntilShardingCompleted();//阻塞至分片完成
        return;
    }
    waitingOtherJobCompleted();
    LiteJobConfiguration liteJobConfig = configService.load(false);//从配置文件中获取任务配置信息
    int shardingTotalCount = liteJobConfig.getTypeConfig().getCoreConfig().getShardingTotalCount();
    log.debug("Job '{}' sharding begin.", jobName);
    jobNodeStorage.fillEphemeralJobNode(ShardingNode.PROCESSING, "");
    resetShardingInfo(shardingTotalCount);//重置分片信息
    JobShardingStrategy jobShardingStrategy = JobShardingStrategyFactory.getStrategy(liteJobConfig.getJobShardingStrategyClass());//获取配置文件中的分片策略
    jobNodeStorage.executeInTransaction(new PersistShardingInfoTransactionExecutionCallback(jobShardingStrategy.sharding(availableJobInstances, jobName, shardingTotalCount)));//根据不同的策略进行分片，这块后续我们再分析
    log.debug("Job '{}' sharding complete.", jobName);
}

分片判断完成后，获取本机的分片项，然后如果开启失效转移，删除本地失效转移项。

言归正传，获取到分片上下文shardingContexts后，判断是否允许发送任务事件。

if (jobFacade.misfireIfRunning(shardingContexts.getShardingItemParameters().keySet())) {//设置任务被错过执行的标记
    if (shardingContexts.isAllowSendJobEvent()) {
        jobFacade.postJobStatusTraceEvent(shardingContexts.getTaskId(), State.TASK_FINISHED, String.format(
                "Previous job '%s' - shardingItems '%s' is still running, misfired job will start after previous job completed.", jobName, 
                shardingContexts.getShardingItemParameters().keySet()));
    }
    return;
}

分片项被错过执行，发布任务事件。下一步，准备执行。

try {
    jobFacade.beforeJobExecuted(shardingContexts);
} catch (final Throwable cause) {
    jobExceptionHandler.handleException(jobName, cause);
}
execute(shardingContexts, JobExecutionEvent.ExecutionSource.NORMAL_TRIGGER);
while (jobFacade.isExecuteMisfired(shardingContexts.getShardingItemParameters().keySet())) {
    jobFacade.clearMisfire(shardingContexts.getShardingItemParameters().keySet());
    execute(shardingContexts, JobExecutionEvent.ExecutionSource.MISFIRE);
}
jobFacade.failoverIfNecessary();
try {
    jobFacade.afterJobExecuted(shardingContexts);
} catch (final Throwable cause) {
    jobExceptionHandler.handleException(jobName, cause);
}

先做一些执行前准备(清理上次执行信息)，然后执行，判断是否开启失效转移，执行成功后做一些执行后处理。

execute(final ShardingContexts shardingContexts, final JobExecutionEvent.ExecutionSource executionSource)

看代码...

if (shardingContexts.getShardingItemParameters().isEmpty()) {
    if (shardingContexts.isAllowSendJobEvent()) {
        jobFacade.postJobStatusTraceEvent(shardingContexts.getTaskId(), State.TASK_FINISHED, String.format("Sharding item for job '%s' is empty.", jobName));
    }
    return;
}
jobFacade.registerJobBegin(shardingContexts);
String taskId = shardingContexts.getTaskId();
if (shardingContexts.isAllowSendJobEvent()) {
    jobFacade.postJobStatusTraceEvent(taskId, State.TASK_RUNNING, "");
}
try {
    process(shardingContexts, executionSource);
} finally {
    // TODO 考虑增加作业失败的状态，并且考虑如何处理作业失败的整体回路
    jobFacade.registerJobCompleted(shardingContexts);
    if (itemErrorMessages.isEmpty()) {
        if (shardingContexts.isAllowSendJobEvent()) {
            jobFacade.postJobStatusTraceEvent(taskId, State.TASK_FINISHED, "");
        }
    } else {
        if (shardingContexts.isAllowSendJobEvent()) {
            jobFacade.postJobStatusTraceEvent(taskId, State.TASK_ERROR, itemErrorMessages.toString());
        }
    }
}

主要做一些前期准备和后期的方法。重点是process方法，我们继续看。

process(final ShardingContexts shardingContexts, final JobExecutionEvent.ExecutionSource executionSource)

Collection<Integer> items = shardingContexts.getShardingItemParameters().keySet();
if (1 == items.size()) {//一个分片，立即执行
    int item = shardingContexts.getShardingItemParameters().keySet().iterator().next();
    JobExecutionEvent jobExecutionEvent =  new JobExecutionEvent(shardingContexts.getTaskId(), jobName, executionSource, item);
    process(shardingContexts, item, jobExecutionEvent);
    return;
}
final CountDownLatch latch = new CountDownLatch(items.size());//多个分片，使用CountDownLatch，并行执行
for (final int each : items) {
    final JobExecutionEvent jobExecutionEvent = new JobExecutionEvent(shardingContexts.getTaskId(), jobName, executionSource, each);
    if (executorService.isShutdown()) {
        return;
    }
    executorService.submit(new Runnable() {
                
        @Override
        public void run() {
            try {
                process(shardingContexts, each, jobExecutionEvent);
            } finally {
                latch.countDown();
            }
        }
    });
}
try {
    latch.await();
} catch (final InterruptedException ex) {
    Thread.currentThread().interrupt();
}

private void process(final ShardingContexts shardingContexts, final int item, final JobExecutionEvent startEvent)

if (shardingContexts.isAllowSendJobEvent()) {
    jobFacade.postJobExecutionEvent(startEvent);
}
log.trace("Job '{}' executing, item is: '{}'.", jobName, item);
JobExecutionEvent completeEvent;
try {
    process(new ShardingContext(shardingContexts, item));
    completeEvent = startEvent.executionSuccess();
    log.trace("Job '{}' executed, item is: '{}'.", jobName, item);
    if (shardingContexts.isAllowSendJobEvent()) {
        jobFacade.postJobExecutionEvent(completeEvent);
    }
} catch (final Throwable cause) {
    completeEvent = startEvent.executionFailure(cause);
    jobFacade.postJobExecutionEvent(completeEvent);
    itemErrorMessages.put(item, ExceptionUtil.transform(cause));
    jobExceptionHandler.handleException(jobName, cause);
}