Elastic-Job原理--任务调度处理（四）

版权声明：欢迎转载 https://blog.csdn.net/qq924862077/article/details/82858684

     在上一篇博客Elastic-Job原理--任务分片策略（三）我们已经了解了Elastic-Job的任务分片策略，这篇博客我们了解学习一下Elastic-Job是如何执行分片任务的。

      首先，Elastic-Job的定时任务执行机制还是基于quartz开发的，因此Elastic-Job实现了Quartz的任务接口Job实现了LiteJob，来根据定时任务规则执行定时任务。

实现Quartz的接口Job

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();
    }
}

根据任务类型JobExecutorFactory会获取任务执行器，然后调用execute方法

    /**
     * 获取作业执行器.
     *
     * @param elasticJob 分布式弹性作业
     * @param jobFacade 作业内部服务门面服务
     * @return 作业执行器
     */
    @SuppressWarnings("unchecked")
    public static AbstractElasticJobExecutor getJobExecutor(final ElasticJob elasticJob, final JobFacade jobFacade) {
        if (null == elasticJob) {
            return new ScriptJobExecutor(jobFacade);
        }
        if (elasticJob instanceof SimpleJob) {
            return new SimpleJobExecutor((SimpleJob) elasticJob, jobFacade);
        }
        if (elasticJob instanceof DataflowJob) {
            return new DataflowJobExecutor((DataflowJob) elasticJob, jobFacade);
        }
        throw new JobConfigurationException("Cannot support job type '%s'", elasticJob.getClass().getCanonicalName());
    }

       Elastic-Job提供了任务执行器抽象类AbstractElasticJobExecutor，在AbstractElasticJobExecutor中会获取任务分片信息及任务失败转移等处理操作。

在execute中会获取所有的分片信息，及一系列的处理操作。

    /**
     * 执行作业.
     */
    public final void execute() {
        try {
            jobFacade.checkJobExecutionEnvironment();
        } catch (final JobExecutionEnvironmentException cause) {
            jobExceptionHandler.handleException(jobName, cause);
        }
		//获取分片信息
        ShardingContexts shardingContexts = jobFacade.getShardingContexts();
        if (shardingContexts.isAllowSendJobEvent()) {
            jobFacade.postJobStatusTraceEvent(shardingContexts.getTaskId(), State.TASK_STAGING, String.format("Job '%s' execute begin.", jobName));
        }
        if (jobFacade.misfireIfRunning(shardingContexts.getShardingItemParameters().keySet())) {
            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;
        }
        try {
            jobFacade.beforeJobExecuted(shardingContexts);
            //CHECKSTYLE:OFF
        } catch (final Throwable cause) {
            //CHECKSTYLE:ON
            jobExceptionHandler.handleException(jobName, cause);
        }
		//执行分片任务
        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);
            //CHECKSTYLE:OFF
        } catch (final Throwable cause) {
            //CHECKSTYLE:ON
            jobExceptionHandler.handleException(jobName, cause);
        }
    }

在execute中会记录一些任务的状态信息，然后执行process方法

private void execute(final ShardingContexts shardingContexts, final JobExecutionEvent.ExecutionSource executionSource) {
        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 {
			//执行分片任务
            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());
                }
            }
        }
    }

在process方法中，会根据分片数量单任务时直接执行，多任务时添加到线程池执行

//根据分片数量依次执行分片任务
private void process(final ShardingContexts shardingContexts, final JobExecutionEvent.ExecutionSource executionSource) {
        Collection<Integer> items = shardingContexts.getShardingItemParameters().keySet();
		//如果只存在一个分片则直接执行
        if (1 == items.size()) {
            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());
		//根据分片数量依次执行分片任务
        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 {
			//等待所有分片任务执行完毕
            latch.await();
        } catch (final InterruptedException ex) {
            Thread.currentThread().interrupt();
        }
    }

调用子类的process方法根据任务类型去执行

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 {
			//执行分片任务
            process(new ShardingContext(shardingContexts, item));
            completeEvent = startEvent.executionSuccess();
            log.trace("Job '{}' executed, item is: '{}'.", jobName, item);
            if (shardingContexts.isAllowSendJobEvent()) {
                jobFacade.postJobExecutionEvent(completeEvent);
            }
            // CHECKSTYLE:OFF
        } catch (final Throwable cause) {
            // CHECKSTYLE:ON
            completeEvent = startEvent.executionFailure(cause);
            jobFacade.postJobExecutionEvent(completeEvent);
            itemErrorMessages.put(item, ExceptionUtil.transform(cause));
            jobExceptionHandler.handleException(jobName, cause);
        }
    }
	

最终根据任务类型，调用AbstractElasticJobExecutor的实现类

/**
 * 简单作业执行器.
 * 
 * @author zhangliang
 */
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);
    }
}