Flume-NG启动过程源码分析（三）(原创)
上一篇文章分析了Flume如何加载配置文件的，动态加载也只是重复运行getConfiguration()。
本篇分析加载配置文件后各个组件是如何运行的？
加载完配置文件订阅者Application类会收到订阅信息执行：
@Subscribe public synchronized void handleConfigurationEvent(MaterializedConfiguration conf) { stopAllComponents(); startAllComponents(conf); }
MaterializedConfiguration conf就是getConfiguration()方法获取的配置信息，是SimpleMaterializedConfiguration的一个实例。
handleConfigurationEvent方法在前面章节(一)中有过大致分析，包括：stopAllComponents()和startAllComponents(conf)。Application中的materializedConfiguration就是MaterializedConfiguration conf，stopAllComponents()方法中的materializedConfiguration是旧的配置信息，需要先停掉旧的组件，然后startAllComponents(conf)将新的配置信息赋给materializedConfiguration并依次启动各个组件。
1、先看startAllComponents(conf)方法。代码如下：
private void startAllComponents(MaterializedConfiguration materializedConfiguration) {//启动所有组件最基本的三大组件 logger.info("Starting new configuration:{}", materializedConfiguration); this.materializedConfiguration = materializedConfiguration; for (Entry<String, Channel> entry : materializedConfiguration.getChannels().entrySet()) { try{ logger.info("Starting Channel " + entry.getKey()); supervisor.supervise(entry.getValue(), new SupervisorPolicy.AlwaysRestartPolicy(), LifecycleState.START); } catch (Exception e){ logger.error("Error while starting {}", entry.getValue(), e); } } /* * Wait for all channels to start.等待所有channel启动完毕 */ for(Channel ch: materializedConfiguration.getChannels().values()){ while(ch.getLifecycleState() != LifecycleState.START && !supervisor.isComponentInErrorState(ch)){ try { logger.info("Waiting for channel: " + ch.getName() + " to start. Sleeping for 500 ms"); Thread.sleep(500); } catch (InterruptedException e) { logger.error("Interrupted while waiting for channel to start.", e); Throwables.propagate(e); } } } for (Entry<String, SinkRunner> entry : materializedConfiguration.getSinkRunners() .entrySet()) { //启动所有sink try{ logger.info("Starting Sink " + entry.getKey()); supervisor.supervise(entry.getValue(), new SupervisorPolicy.AlwaysRestartPolicy(), LifecycleState.START); } catch (Exception e) { logger.error("Error while starting {}", entry.getValue(), e); } } for (Entry<String, SourceRunner> entry : materializedConfiguration .getSourceRunners().entrySet()) {//启动所有source try{ logger.info("Starting Source " + entry.getKey()); supervisor.supervise(entry.getValue(), new SupervisorPolicy.AlwaysRestartPolicy(), LifecycleState.START); } catch (Exception e) { logger.error("Error while starting {}", entry.getValue(), e); } } this.loadMonitoring(); }
三大组件都是通过supervisor.supervise(entry.getValue(),new SupervisorPolicy.AlwaysRestartPolicy(), LifecycleState.START)启动的，其中，channel启动之后还要待所有的channel完全启动完毕之后才可再去启动sink和source。如果channel没有启动完毕就去启动另外俩组件，会出现错误，以为一旦sink或者source建立完毕就会立即与channel通信获取数据。稍后会分别分析sink和source的启动。
supervisor是LifecycleSupervisor的一个对象，该类的构造方法会构造一个有10个线程，上限是20的线程池供各大组件使用。构造方法如下：
public LifecycleSupervisor() { lifecycleState = LifecycleState.IDLE; supervisedProcesses = new HashMap<LifecycleAware, Supervisoree>();//存储所有历史上的组件及其监控信息 monitorFutures = new HashMap<LifecycleAware, ScheduledFuture<?>>(); monitorService = new ScheduledThreadPoolExecutor(10, new ThreadFactoryBuilder().setNameFormat( "lifecycleSupervisor-" + Thread.currentThread().getId() + "-%d") .build()); monitorService.setMaximumPoolSize(20); monitorService.setKeepAliveTime(30, TimeUnit.SECONDS); purger = new Purger(); needToPurge = false; }
supervise(LifecycleAware lifecycleAware,SupervisorPolicy policy, LifecycleState desiredState)方法则是具体执行启动各个组件的方法。flume的所有组件均实现自
LifecycleAware 接口，如图：
，这个接口就三个方法getLifecycleState(返回组件运行状态)、start(组件启动)、stop(停止组件)。supervise方法代码如下：
public synchronized void supervise(LifecycleAware lifecycleAware, SupervisorPolicy policy, LifecycleState desiredState) {
//检查线程池状态 if(this.monitorService.isShutdown() || this.monitorService.isTerminated() || this.monitorService.isTerminating()){ throw new FlumeException("Supervise called on " + lifecycleAware + " " + "after shutdown has been initiated. " + lifecycleAware + " will not" + " be started"); } //如果该组件已经在监控，则拒绝二次监控 Preconditions.checkState(!supervisedProcesses.containsKey(lifecycleAware), "Refusing to supervise " + lifecycleAware + " more than once"); if (logger.isDebugEnabled()) { logger.debug("Supervising service:{} policy:{} desiredState:{}", new Object[] { lifecycleAware, policy, desiredState }); } //新的组件 Supervisoree process = new Supervisoree(); process.status = new Status(); process.policy = policy; process.status.desiredState = desiredState; process.status.error = false; MonitorRunnable monitorRunnable = new MonitorRunnable(); monitorRunnable.lifecycleAware = lifecycleAware;//组件 monitorRunnable.supervisoree = process; monitorRunnable.monitorService = monitorService; supervisedProcesses.put(lifecycleAware, process); //创建并执行一个在给定初始延迟后首次启用的定期操作，随后，在每一次执行终止和下一次执行开始之间都存在给定的延迟。如果任务的任一执行遇到异常，就会取消后续执行。 ScheduledFuture<?> future = monitorService.scheduleWithFixedDelay( monitorRunnable, 0, 3, TimeUnit.SECONDS); //启动MonitorRunnable,结束之后3秒再重新启动，可以用于重试 monitorFutures.put(lifecycleAware, future); }
该方法首先monitorService是否是正常运行状态；然后构造Supervisoree process = new Supervisoree()，进行赋值并构造一个监控进程MonitorRunnable，放入线程池去执行。
MonitorRunnable.run()方法：
public void run() { logger.debug("checking process:{} supervisoree:{}", lifecycleAware, supervisoree); long now = System.currentTimeMillis();//获取现在的时间戳 try { if (supervisoree.status.firstSeen == null) { logger.debug("first time seeing {}", lifecycleAware); //如果这个组件是是初次受监控 supervisoree.status.firstSeen = now; } //如果这个组件已经监控过 supervisoree.status.lastSeen = now; synchronized (lifecycleAware) {//锁住组件 if (supervisoree.status.discard) {//该组件已经停止监控 // Unsupervise has already been called on this. logger.info("Component has already been stopped {}", lifecycleAware); return;//直接返回 } else if (supervisoree.status.error) {//该组件是错误状态 logger.info("Component {} is in error state, and Flume will not" + "attempt to change its state", lifecycleAware); return;//直接返回 } supervisoree.status.lastSeenState = lifecycleAware.getLifecycleState();//获取组件最新状态,没运行start()方法之前是LifecycleState.IDLE状态 if (!lifecycleAware.getLifecycleState().equals( supervisoree.status.desiredState)) {//该组件最新状态和期望的状态不一致 logger.debug("Want to transition {} from {} to {} (failures:{})", new Object[] { lifecycleAware, supervisoree.status.lastSeenState, supervisoree.status.desiredState, supervisoree.status.failures }); switch (supervisoree.status.desiredState) {//根据状态执行相应的操作 case START: try { lifecycleAware.start(); //启动组件，同时其状态也会变为LifecycleState.START } catch (Throwable e) { logger.error("Unable to start " + lifecycleAware + " - Exception follows.", e); if (e instanceof Error) { // This component can never recover, shut it down. supervisoree.status.desiredState = LifecycleState.STOP; try { lifecycleAware.stop(); logger.warn("Component {} stopped, since it could not be" + "successfully started due to missing dependencies", lifecycleAware); } catch (Throwable e1) { logger.error("Unsuccessful attempt to " + "shutdown component: {} due to missing dependencies." + " Please shutdown the agent" + "or disable this component, or the agent will be" + "in an undefined state.", e1); supervisoree.status.error = true; if (e1 instanceof Error) { throw (Error) e1; } // Set the state to stop, so that the conf poller can // proceed. } } supervisoree.status.failures++;//启动错误失败次数+1 } break; case STOP: try { lifecycleAware.stop(); //停止组件 } catch (Throwable e) { logger.error("Unable to stop " + lifecycleAware + " - Exception follows.", e); if (e instanceof Error) { throw (Error) e; } supervisoree.status.failures++; //组件停止错误，错误次数+1 } break; default: logger.warn("I refuse to acknowledge {} as a desired state", supervisoree.status.desiredState); } //两种SupervisorPolicy(AlwaysRestartPolicy和OnceOnlyPolicy)后者还未使用过，前者表示可以重新启动的组件，后者表示只能运行一次的组件 if (!supervisoree.policy.isValid(lifecycleAware, supervisoree.status)) { logger.error( "Policy {} of {} has been violated - supervisor should exit!", supervisoree.policy, lifecycleAware); } } } } catch(Throwable t) { logger.error("Unexpected error", t); } logger.debug("Status check complete"); }
上面的 lifecycleAware.stop()和lifecycleAware.start()就是执行的sink、source、channel等的对应方法。
这里的start需要注意如果是channel则是直接执行start方法；如果是sink或者PollableSource的实现类，则会在start()方法中启动一个线程来循环的调用process()方法来从channel拿数据(sink)或者向channel送数据(source);如果是EventDrivenSource的实现类，则没有process()方法，通过执行start()来执行想channel中送数据的操作(可以在此添加线程来实现相应的逻辑)。
2、stopAllComponents()方法。顾名思义，就是停止所有组件的方法。该方法代码如下：
private void stopAllComponents() { if (this.materializedConfiguration != null) { logger.info("Shutting down configuration: {}", this.materializedConfiguration); for (Entry<String, SourceRunner> entry : this.materializedConfiguration .getSourceRunners().entrySet()) { try{ logger.info("Stopping Source " + entry.getKey()); supervisor.unsupervise(entry.getValue()); } catch (Exception e){ logger.error("Error while stopping {}", entry.getValue(), e); } } for (Entry<String, SinkRunner> entry : this.materializedConfiguration.getSinkRunners().entrySet()) { try{ logger.info("Stopping Sink " + entry.getKey()); supervisor.unsupervise(entry.getValue()); } catch (Exception e){ logger.error("Error while stopping {}", entry.getValue(), e); } } for (Entry<String, Channel> entry : this.materializedConfiguration.getChannels().entrySet()) { try{ logger.info("Stopping Channel " + entry.getKey()); supervisor.unsupervise(entry.getValue()); } catch (Exception e){ logger.error("Error while stopping {}", entry.getValue(), e); } } } if(monitorServer != null) { monitorServer.stop(); } }
首先，需要注意的是，stopAllComponents()放在startAllComponents(MaterializedConfiguration materializedConfiguration)方法之前的原因，由于配置文件的动态加载这一特性的存在，使得每次加载之前都要先把旧的组件停掉，然后才能去加载最新配置文件中的配置；
其次，首次执行stopAllComponents()时，由于配置文件尚未赋值，所以并不会执行停止所有组件的操作以及停止monitorServer。再次加载时会依照顺序依次停止对source、sink以及channel的监控，通过supervisor.unsupervise(entry.getValue())停止对其的监控，然后停止monitorServer。supervisor.unsupervise方法如下：
public synchronized void unsupervise(LifecycleAware lifecycleAware) { Preconditions.checkState(supervisedProcesses.containsKey(lifecycleAware), "Unaware of " + lifecycleAware + " - can not unsupervise"); logger.debug("Unsupervising service:{}", lifecycleAware); synchronized (lifecycleAware) { Supervisoree supervisoree = supervisedProcesses.get(lifecycleAware); supervisoree.status.discard = true; this.setDesiredState(lifecycleAware, LifecycleState.STOP); logger.info("Stopping component: {}", lifecycleAware); lifecycleAware.stop(); } supervisedProcesses.remove(lifecycleAware); //We need to do this because a reconfiguration simply unsupervises old //components and supervises new ones. monitorFutures.get(lifecycleAware).cancel(false); //purges are expensive, so it is done only once every 2 hours. needToPurge = true; monitorFutures.remove(lifecycleAware); }
该方法首先会检查正在运行的组件当中是否有此组件supervisedProcesses.containsKey(lifecycleAware)；如果存在，则对此组件标记为已取消监控supervisoree.status.discard = true；将状态设置为STOP，并停止组件lifecycleAware.stop()；然后从删除此组件的监控记录，包括从记录正在处于监控的组件的结构supervisedProcesses以及记录组件及其对应的运行线程的结构monitorFutures中删除相应的组件信息，并且needToPurge = true会使得两小时执行一次的线程池清理操作。
有一个问题就是，sink和source是如何找到对应的channel的呢？？其实前面章节就已经讲解过，分别在AbstractConfigurationProvider.loadSources方法中通过ChannelSelector配置source对应的channel，而在source中通过getChannelProcessor()获取channels,通过channelProcessor.processEventBatch(eventList)将events发送到channel中；而在AbstractConfigurationProvider.loadSinks方法中sink.setChannel(channelComponent.channel)来设置此sink对应的channel，然后在sink的实现类中通过getChannel()获取设置的channel，并使用channel.take()从channel中获取event进行处理。
以上三节是Flume-NG的启动、配置文件的加载、配置文件的动态加载、组件的执行的整个流程。文中的疏漏之处，请各位指教，我依然会后续继续完善这些内容的。
后续还有更精彩的章节。。。。