Xxl Job 源码分析(三) -- 添加任务并执行任务
从之前的 Xxl Job Helloworld 中学会了简单的使用 Xxl-Job 进行分步式任务调度。并且可以知道当我使用 Xxl-Job时，我们核心基本需要以下三个步骤：
- 启动调度中心(xxl-job-admin)
- 启动执行器(引用xxl-job-core 的业务代码)
- 调度中心添加任务并执行任务
经过以上的三个步骤，然后添加的任务就可以执行了。下面我们就来从源码的角度分析一下：上面 3 个步骤都做了什么事，使得任务可以定时调度的。所以我决定分为三篇 blog 来分析 xxl-job 的源码实现。使用的 xxl-job 是最新版本 2.2.0-SNAPSHOT。
1、调度中心添加任务
从之前的 Xxl Job Helloworld 使用 xxl job 进行定时调度的时候的添加任务的时候会首先通过 执行器管理 添加执行器。
它其实是通过调用 JobGroupController 来管理执行器的。根据名称我们也可以很清楚的明白。它其实是把 job 按照不同的调度器来进行分组的。用来管理不同调度器各个具体的任务。
第二步就是在 任务管理 模块中添加具体的任务，首先先选择一个已经配置好的执行器，然后再添加任务。
根据具体的任务类型配置 job，与执行器关联起来。使得调度中心可以通过执行器远程执行执行器中的任务。
2、调度中心远程调用执行器
在 [Xxl Job 源码分析(一) – 启动调度中心] 中的最后我们分析到 JobScheduleHelper 会死循环从 xxl_job_info表中取出未来5秒内要执行的任务，进行调度分发。分为三个分支来处理查询到的任务：
-
第一个分支当前任务的触发时间已经超时5秒以上了，不在执行，直接计算下一次触发时间。
-
第二个分支为触发时间已满足，利用JobTriggerPoolHelper这个类进行任务调度，之后判断下一次执行时间如果在5秒内，进行此任务数据的缓存，处理逻辑与第三个分支一样。
-
第三个分支就是对触发时间秒数进行60取模，跟进pushTimeRing方法。
当任务需要调度的时候最终都会通过 JobTriggerPoolHelper#trigger 方法来进行任务调度，下面我们就以这个方法以起点，来分析一下调度中心是如何进行远程调度的。
它首先会调用 JobTriggerPoolHelper#addTrigger ，通过任务远程调度任务的超时次数选择快/慢线程池来执行任务。接着再调用 XxlJobTrigger#trigger。
它主要的作用是加载任务以及任务所在的执行器。看任务是否需要分片执行。执行条件是任务配置的是广播模式并且执行器注册的个数大于 1.下一步就是执行真正的任务调度了。
private static void processTrigger(XxlJobGroup group, XxlJobInfo jobInfo, int finalFailRetryCount, TriggerTypeEnum triggerType, int index, int total){
// param
ExecutorBlockStrategyEnum blockStrategy = ExecutorBlockStrategyEnum.match(jobInfo.getExecutorBlockStrategy(), ExecutorBlockStrategyEnum.SERIAL_EXECUTION); // block strategy
ExecutorRouteStrategyEnum executorRouteStrategyEnum = ExecutorRouteStrategyEnum.match(jobInfo.getExecutorRouteStrategy(), null); // route strategy
String shardingParam = (ExecutorRouteStrategyEnum.SHARDING_BROADCAST==executorRouteStrategyEnum)?String.valueOf(index).concat("/").concat(String.valueOf(total)):null;
// 1、save log-id
XxlJobLog jobLog = new XxlJobLog();
jobLog.setJobGroup(jobInfo.getJobGroup());
jobLog.setJobId(jobInfo.getId());
jobLog.setTriggerTime(new Date());
XxlJobAdminConfig.getAdminConfig().getXxlJobLogDao().save(jobLog);
logger.debug(">>>>>>>>>>> xxl-job trigger start, jobId:{}", jobLog.getId());
// 2、init trigger-param
TriggerParam triggerParam = new TriggerParam();
triggerParam.setJobId(jobInfo.getId());
triggerParam.setExecutorHandler(jobInfo.getExecutorHandler());
triggerParam.setExecutorParams(jobInfo.getExecutorParam());
triggerParam.setExecutorBlockStrategy(jobInfo.getExecutorBlockStrategy());
triggerParam.setExecutorTimeout(jobInfo.getExecutorTimeout());
triggerParam.setLogId(jobLog.getId());
triggerParam.setLogDateTime(jobLog.getTriggerTime().getTime());
triggerParam.setGlueType(jobInfo.getGlueType());
triggerParam.setGlueSource(jobInfo.getGlueSource());
triggerParam.setGlueUpdatetime(jobInfo.getGlueUpdatetime().getTime());
triggerParam.setBroadcastIndex(index);
triggerParam.setBroadcastTotal(total);
// 3、init address
String address = null;
ReturnT routeAddressResult = null;
if (group.getRegistryList()!=null && !group.getRegistryList().isEmpty()) {
if (ExecutorRouteStrategyEnum.SHARDING_BROADCAST == executorRouteStrategyEnum) {
if (index < group.getRegistryList().size()) {
address = group.getRegistryList().get(index);
} else {
address = group.getRegistryList().get(0);
}
} else {
routeAddressResult = executorRouteStrategyEnum.getRouter().route(triggerParam, group.getRegistryList());
if (routeAddressResult.getCode() == ReturnT.SUCCESS_CODE) {
address = routeAddressResult.getContent();
}
}
} else {
routeAddressResult = new ReturnT(ReturnT.FAIL_CODE, I18nUtil.getString("jobconf_trigger_address_empty"));
}
// 4、trigger remote executor
ReturnT triggerResult = null;
if (address != null) {
triggerResult = runExecutor(triggerParam, address);
} else {
triggerResult = new ReturnT(ReturnT.FAIL_CODE, null);
}
// 5、collection trigger info
StringBuffer triggerMsgSb = new StringBuffer();
triggerMsgSb.append(I18nUtil.getString("jobconf_trigger_type")).append("：").append(triggerType.getTitle());
triggerMsgSb.append("
").append(I18nUtil.getString("jobconf_trigger_admin_adress")).append("：").append(IpUtil.getIp());
triggerMsgSb.append("
").append(I18nUtil.getString("jobconf_trigger_exe_regtype")).append("：")
.append( (group.getAddressType() == 0)?I18nUtil.getString("jobgroup_field_addressType_0"):I18nUtil.getString("jobgroup_field_addressType_1") );
triggerMsgSb.append("
").append(I18nUtil.getString("jobconf_trigger_exe_regaddress")).append("：").append(group.getRegistryList());
triggerMsgSb.append("
").append(I18nUtil.getString("jobinfo_field_executorRouteStrategy")).append("：").append(executorRouteStrategyEnum.getTitle());
if (shardingParam != null) {
triggerMsgSb.append("("+shardingParam+")");
}
triggerMsgSb.append("
").append(I18nUtil.getString("jobinfo_field_executorBlockStrategy")).append("：").append(blockStrategy.getTitle());
triggerMsgSb.append("
").append(I18nUtil.getString("jobinfo_field_timeout")).append("：").append(jobInfo.getExecutorTimeout());
triggerMsgSb.append("
").append(I18nUtil.getString("jobinfo_field_executorFailRetryCount")).append("：").append(finalFailRetryCount);
triggerMsgSb.append("
>>>>>>>>>>>"+ I18nUtil.getString("jobconf_trigger_run") +"<<<<<<<<<<<
")
.append((routeAddressResult!=null&&routeAddressResult.getMsg()!=null)?routeAddressResult.getMsg()+"
":"").append(triggerResult.getMsg()!=null?triggerResult.getMsg():"");
// 6、save log trigger-info
jobLog.setExecutorAddress(address);
jobLog.setExecutorHandler(jobInfo.getExecutorHandler());
jobLog.setExecutorParam(jobInfo.getExecutorParam());
jobLog.setExecutorShardingParam(shardingParam);
jobLog.setExecutorFailRetryCount(finalFailRetryCount);
//jobLog.setTriggerTime();
jobLog.setTriggerCode(triggerResult.getCode());
jobLog.setTriggerMsg(triggerMsgSb.toString());
XxlJobAdminConfig.getAdminConfig().getXxlJobLogDao().updateTriggerInfo(jobLog);
logger.debug(">>>>>>>>>>> xxl-job trigger end, jobId:{}", jobLog.getId());
}
它分为 6 个小步骤：
- 保存任务执行日志信息，此时为空还记得第二篇的回调吗？它任务执行完之后会把执行完的日志回调给调度中心。然后调度中心就会把任务执行的日志以及任务重试的日志都保存到调度中心。
- 初始化远程调度的参数，包括日志 ID，执行任务的 bean 名称，分片信息、Glue 任务信息等。
- 根据执行器信息以及路由规则选择合适的执行器地址进行远程调用
- 调用远程执行器
public static ReturnT runExecutor(TriggerParam triggerParam, String address){
ExecutorBiz executorBiz = XxlJobScheduler.getExecutorBiz(address);
runResult = executorBiz.run(triggerParam);
}
- 收集调度信息
- 把调度信息保存到数据库
然后下面就是通过 xxl-rpc 获取到 ExecutorBiz 的代码对象。
XxlJobScheduler#getExecutorBiz
public static ExecutorBiz getExecutorBiz(String address) throws Exception {
// valid
if (address==null || address.trim().length()==0) {
return null;
}
// load-cache
address = address.trim();
ExecutorBiz executorBiz = executorBizRepository.get(address);
if (executorBiz != null) {
return executorBiz;
}
// set-cache
XxlRpcReferenceBean referenceBean = new XxlRpcReferenceBean();
referenceBean.setClient(NettyHttpClient.class);
referenceBean.setSerializer(HessianSerializer.class);
referenceBean.setCallType(CallType.SYNC);
referenceBean.setLoadBalance(LoadBalance.ROUND);
referenceBean.setIface(ExecutorBiz.class);
referenceBean.setVersion(null);
referenceBean.setTimeout(3000);
referenceBean.setAddress(address);
referenceBean.setAccessToken(XxlJobAdminConfig.getAdminConfig().getAccessToken());
referenceBean.setInvokeCallback(null);
referenceBean.setInvokerFactory(null);
executorBiz = (ExecutorBiz) referenceBean.getObject();
executorBizRepository.put(address, executorBiz);
return executorBiz;
}
最终会通过 XxlRpcReferenceBean#getObject 创建的代理对象远程调用在 Xxl Job 源码分析(二) – 启动执行器 暴露出来的服务。
3、执行器接收请求并运行任务
在第二篇文章的结束只是简单的说了在执行器中 NettyHttpServerHandler 会接收调度中心发送的请求。这个其实是属于 xxl-rpc 里面的内容了。主要是为了大家更加明白，所以我就讲一下。
- 对接收到二字进字符进行非空判断
- 把请求反序列化成 XxlRpcRequest
- 通过 XxlRpcProviderFactory#invokeService 调用服务
- 把调用结果序列化并写入响应
XxlRpcProviderFactory#invokeService
public XxlRpcResponse invokeService(XxlRpcRequest xxlRpcRequest) {
// make response
XxlRpcResponse xxlRpcResponse = new XxlRpcResponse();
xxlRpcResponse.setRequestId(xxlRpcRequest.getRequestId());
// match service bean
String serviceKey = makeServiceKey(xxlRpcRequest.getClassName(), xxlRpcRequest.getVersion());
Object serviceBean = serviceData.get(serviceKey);
// valid
if (serviceBean == null) {
xxlRpcResponse.setErrorMsg("The serviceKey["+ serviceKey +"] not found.");
return xxlRpcResponse;
}
if (System.currentTimeMillis() - xxlRpcRequest.getCreateMillisTime() > 3*60*1000) {
xxlRpcResponse.setErrorMsg("The timestamp difference between admin and executor exceeds the limit.");
return xxlRpcResponse;
}
if (accessToken!=null && accessToken.trim().length()>0 && !accessToken.trim().equals(xxlRpcRequest.getAccessToken())) {
xxlRpcResponse.setErrorMsg("The access token[" + xxlRpcRequest.getAccessToken() + "] is wrong.");
return xxlRpcResponse;
}
try {
// invoke
Class serviceClass = serviceBean.getClass();
String methodName = xxlRpcRequest.getMethodName();
Class[] parameterTypes = xxlRpcRequest.getParameterTypes();
Object[] parameters = xxlRpcRequest.getParameters();
Method method = serviceClass.getMethod(methodName, parameterTypes);
method.setAccessible(true);
Object result = method.invoke(serviceBean, parameters);
/*FastClass serviceFastClass = FastClass.create(serviceClass);
FastMethod serviceFastMethod = serviceFastClass.getMethod(methodName, parameterTypes);
Object result = serviceFastMethod.invoke(serviceBean, parameters);*/
xxlRpcResponse.setResult(result);
} catch (Throwable t) {
// catch error
logger.error("xxl-rpc provider invokeService error.", t);
xxlRpcResponse.setErrorMsg(ThrowableUtil.toString(t));
}
return xxlRpcResponse;
}
我们以 spring bean 模式的远程任务调度举例这个代码。在执行器初始化 RPC 服务提供者的时候会把暴露服务的 ExecutorBiz 接口以及它的实现类 ExecutorBizImpl 类传递进来。
也就是：
之前我们也说过 ExecutorBiz 中定义了任务相关的操作。
public interface ExecutorBiz {
public ReturnT beat();
public ReturnT idleBeat(int jobId);
public ReturnT kill(int jobId);
public ReturnT log(long logDateTim, long logId, int fromLineNum);
public ReturnT run(TriggerParam triggerParam);
}
然后我们再回到上面的 XxlRpcProviderFactory#invokeService 为了大家方便我再贴一下代码。
public XxlRpcResponse invokeService(XxlRpcRequest xxlRpcRequest) {
// make response
XxlRpcResponse xxlRpcResponse = new XxlRpcResponse();
xxlRpcResponse.setRequestId(xxlRpcRequest.getRequestId());
// match service bean
String serviceKey = makeServiceKey(xxlRpcRequest.getClassName(), xxlRpcRequest.getVersion());
Object serviceBean = serviceData.get(serviceKey);
// valid
if (serviceBean == null) {
xxlRpcResponse.setErrorMsg("The serviceKey["+ serviceKey +"] not found.");
return xxlRpcResponse;
}
if (System.currentTimeMillis() - xxlRpcRequest.getCreateMillisTime() > 3*60*1000) {
xxlRpcResponse.setErrorMsg("The timestamp difference between admin and executor exceeds the limit.");
return xxlRpcResponse;
}
if (accessToken!=null && accessToken.trim().length()>0 && !accessToken.trim().equals(xxlRpcRequest.getAccessToken())) {
xxlRpcResponse.setErrorMsg("The access token[" + xxlRpcRequest.getAccessToken() + "] is wrong.");
return xxlRpcResponse;
}
try {
// invoke
Class serviceClass = serviceBean.getClass();
String methodName = xxlRpcRequest.getMethodName();
Class[] parameterTypes = xxlRpcRequest.getParameterTypes();
Object[] parameters = xxlRpcRequest.getParameters();
Method method = serviceClass.getMethod(methodName, parameterTypes);
method.setAccessible(true);
Object result = method.invoke(serviceBean, parameters);
/*FastClass serviceFastClass = FastClass.create(serviceClass);
FastMethod serviceFastMethod = serviceFastClass.getMethod(methodName, parameterTypes);
Object result = serviceFastMethod.invoke(serviceBean, parameters);*/
xxlRpcResponse.setResult(result);
} catch (Throwable t) {
// catch error
logger.error("xxl-rpc provider invokeService error.", t);
xxlRpcResponse.setErrorMsg(ThrowableUtil.toString(t));
}
return xxlRpcResponse;
}
首先它根据远程调用的 ExecutorBiz 接口获取到 ExecutorBizImpl 具体实现类，然后调用它的 run 方法。
public ReturnT run(TriggerParam triggerParam) {
// load old：jobHandler + jobThread
JobThread jobThread = XxlJobExecutor.loadJobThread(triggerParam.getJobId());
IJobHandler jobHandler = jobThread!=null?jobThread.getHandler():null;
String removeOldReason = null;
// valid：jobHandler + jobThread
GlueTypeEnum glueTypeEnum = GlueTypeEnum.match(triggerParam.getGlueType());
if (GlueTypeEnum.BEAN == glueTypeEnum) {
// new jobhandler
IJobHandler newJobHandler = XxlJobExecutor.loadJobHandler(triggerParam.getExecutorHandler());
// valid old jobThread
if (jobThread!=null && jobHandler != newJobHandler) {
// change handler, need kill old thread
removeOldReason = "change jobhandler or glue type, and terminate the old job thread.";
jobThread = null;
jobHandler = null;
}
// valid handler
if (jobHandler == null) {
jobHandler = newJobHandler;
if (jobHandler == null) {
return new ReturnT(ReturnT.FAIL_CODE, "job handler [" + triggerParam.getExecutorHandler() + "] not found.");
}
}
} else if (GlueTypeEnum.GLUE_GROOVY == glueTypeEnum) {
// valid old jobThread
if (jobThread != null &&
!(jobThread.getHandler() instanceof GlueJobHandler
&& ((GlueJobHandler) jobThread.getHandler()).getGlueUpdatetime()==triggerParam.getGlueUpdatetime() )) {
// change handler or gluesource updated, need kill old thread
removeOldReason = "change job source or glue type, and terminate the old job thread.";
jobThread = null;
jobHandler = null;
}
// valid handler
if (jobHandler == null) {
try {
IJobHandler originJobHandler = GlueFactory.getInstance().loadNewInstance(triggerParam.getGlueSource());
jobHandler = new GlueJobHandler(originJobHandler, triggerParam.getGlueUpdatetime());
} catch (Exception e) {
logger.error(e.getMessage(), e);
return new ReturnT(ReturnT.FAIL_CODE, e.getMessage());
}
}
} else if (glueTypeEnum!=null && glueTypeEnum.isScript()) {
// valid old jobThread
if (jobThread != null &&
!(jobThread.getHandler() instanceof ScriptJobHandler
&& ((ScriptJobHandler) jobThread.getHandler()).getGlueUpdatetime()==triggerParam.getGlueUpdatetime() )) {
// change script or gluesource updated, need kill old thread
removeOldReason = "change job source or glue type, and terminate the old job thread.";
jobThread = null;
jobHandler = null;
}
// valid handler
if (jobHandler == null) {
jobHandler = new ScriptJobHandler(triggerParam.getJobId(), triggerParam.getGlueUpdatetime(), triggerParam.getGlueSource(), GlueTypeEnum.match(triggerParam.getGlueType()));
}
} else {
return new ReturnT(ReturnT.FAIL_CODE, "glueType[" + triggerParam.getGlueType() + "] is not valid.");
}
// executor block strategy
if (jobThread != null) {
ExecutorBlockStrategyEnum blockStrategy = ExecutorBlockStrategyEnum.match(triggerParam.getExecutorBlockStrategy(), null);
if (ExecutorBlockStrategyEnum.DISCARD_LATER == blockStrategy) {
// discard when running
if (jobThread.isRunningOrHasQueue()) {
return new ReturnT(ReturnT.FAIL_CODE, "block strategy effect："+ExecutorBlockStrategyEnum.DISCARD_LATER.getTitle());
}
} else if (ExecutorBlockStrategyEnum.COVER_EARLY == blockStrategy) {
// kill running jobThread
if (jobThread.isRunningOrHasQueue()) {
removeOldReason = "block strategy effect：" + ExecutorBlockStrategyEnum.COVER_EARLY.getTitle();
jobThread = null;
}
} else {
// just queue trigger
}
}
// replace thread (new or exists invalid)
if (jobThread == null) {
jobThread = XxlJobExecutor.registJobThread(triggerParam.getJobId(), jobHandler, removeOldReason);
}
// push data to queue
ReturnT pushResult = jobThread.pushTriggerQueue(triggerParam);
return pushResult;
}
如果是 spring bean 模式它会根据配置的 JobHandler 也就是 bean 名称找到对应的任务处理类。如果根据调度中心传过来的 jobId 找不到 JobThread 就通过 XxlJobExecutor 新创建一个 JobThread 进行运行，如果能够找到就把需要运行的任务添加到已有 JobThread 的队列中。下面就是 JobThread 的执行过程：
JobThread#run
public void run() {
// init
try {
handler.init();
} catch (Throwable e) {
logger.error(e.getMessage(), e);
}
// execute
while(!toStop){
running = false;
idleTimes++;
TriggerParam triggerParam = null;
ReturnT executeResult = null;
try {
// to check toStop signal, we need cycle, so wo cannot use queue.take(), instand of poll(timeout)
triggerParam = triggerQueue.poll(3L, TimeUnit.SECONDS);
if (triggerParam!=null) {
running = true;
idleTimes = 0;
triggerLogIdSet.remove(triggerParam.getLogId());
// log filename, like "logPath/yyyy-MM-dd/9999.log"
String logFileName = XxlJobFileAppender.makeLogFileName(new Date(triggerParam.getLogDateTime()), triggerParam.getLogId());
XxlJobFileAppender.contextHolder.set(logFileName);
ShardingUtil.setShardingVo(new ShardingUtil.ShardingVO(triggerParam.getBroadcastIndex(), triggerParam.getBroadcastTotal()));
// execute
XxlJobLogger.log("
----------- xxl-job job execute start -----------
----------- Param:" + triggerParam.getExecutorParams());
if (triggerParam.getExecutorTimeout() > 0) {
// limit timeout
Thread futureThread = null;
try {
final TriggerParam triggerParamTmp = triggerParam;
FutureTask> futureTask = new FutureTask>(new Callable>() {
@Override
public ReturnT call() throws Exception {
return handler.execute(triggerParamTmp.getExecutorParams());
}
});
futureThread = new Thread(futureTask);
futureThread.start();
executeResult = futureTask.get(triggerParam.getExecutorTimeout(), TimeUnit.SECONDS);
} catch (TimeoutException e) {
XxlJobLogger.log("
----------- xxl-job job execute timeout");
XxlJobLogger.log(e);
executeResult = new ReturnT(IJobHandler.FAIL_TIMEOUT.getCode(), "job execute timeout ");
} finally {
futureThread.interrupt();
}
} else {
// just execute
executeResult = handler.execute(triggerParam.getExecutorParams());
}
if (executeResult == null) {
executeResult = IJobHandler.FAIL;
} else {
executeResult.setMsg(
(executeResult!=null&&executeResult.getMsg()!=null&&executeResult.getMsg().length()>50000)
?executeResult.getMsg().substring(0, 50000).concat("...")
:executeResult.getMsg());
executeResult.setContent(null); // limit obj size
}
XxlJobLogger.log("
----------- xxl-job job execute end(finish) -----------
----------- ReturnT:" + executeResult);
} else {
if (idleTimes > 30) {
if(triggerQueue.size() == 0) { // avoid concurrent trigger causes jobId-lost
XxlJobExecutor.removeJobThread(jobId, "excutor idel times over limit.");
}
}
}
} catch (Throwable e) {
if (toStop) {
XxlJobLogger.log("
----------- JobThread toStop, stopReason:" + stopReason);
}
StringWriter stringWriter = new StringWriter();
e.printStackTrace(new PrintWriter(stringWriter));
String errorMsg = stringWriter.toString();
executeResult = new ReturnT(ReturnT.FAIL_CODE, errorMsg);
XxlJobLogger.log("
----------- JobThread Exception:" + errorMsg + "
----------- xxl-job job execute end(error) -----------");
} finally {
if(triggerParam != null) {
// callback handler info
if (!toStop) {
// commonm
TriggerCallbackThread.pushCallBack(new HandleCallbackParam(triggerParam.getLogId(), triggerParam.getLogDateTime(), executeResult));
} else {
// is killed
ReturnT stopResult = new ReturnT(ReturnT.FAIL_CODE, stopReason + " [job running, killed]");
TriggerCallbackThread.pushCallBack(new HandleCallbackParam(triggerParam.getLogId(), triggerParam.getLogDateTime(), stopResult));
}
}
}
}
// callback trigger request in queue
while(triggerQueue !=null && triggerQueue.size()>0){
TriggerParam triggerParam = triggerQueue.poll();
if (triggerParam!=null) {
// is killed
ReturnT stopResult = new ReturnT(ReturnT.FAIL_CODE, stopReason + " [job not executed, in the job queue, killed.]");
TriggerCallbackThread.pushCallBack(new HandleCallbackParam(triggerParam.getLogId(), triggerParam.getLogDateTime(), stopResult));
}
}
// destroy
try {
handler.destroy();
} catch (Throwable e) {
logger.error(e.getMessage(), e);
}
logger.info(">>>>>>>>>>> xxl-job JobThread stoped, hashCode:{}", Thread.currentThread());
}
}
- 执行 IJobHandler#init 方法
- 查看 triggerQueue 队列中是否有任务需要执行
- 如果 triggerParam 不为空则继续执行
- 创建日志文件，比如：logPath/yyyy-MM-dd/9999.log
- com.xxl.job.core.handler.IJobHandler#execute 执行具体的任务
- 调用 TriggerCallbackThread#pushCallBack 把任务执行的日志以及重试日志回写到调度中心
至此整个 xxl-job 如何进行分步式任务调度就完成了。