Flume-ng源码解析之启动流程

今天我们通过阅读Flume-NG的源码来看看Flume的整个启动流程，废话不多说，翠花，上源码！！

1 主类也是启动类

在这里我贴出Application中跟启动有关的方法，其他你们可以自己看源码，毕竟源码解析解的是思路。

org.apache.flume.node.Application

  /*主函数*/
  public static void main(String[] args) {

    try {

      boolean isZkConfigured = false;

      Options options = new Options();

      Option option = new Option("n", "name", true, "the name of this agent");
      option.setRequired(true);
      options.addOption(option);

      option = new Option("f", "conf-file", true,
          "specify a config file (required if -z missing)");
      option.setRequired(false);
      options.addOption(option);

      option = new Option(null, "no-reload-conf", false,
          "do not reload config file if changed");
      options.addOption(option);

      // Options for Zookeeper
      option = new Option("z", "zkConnString", true,
          "specify the ZooKeeper connection to use (required if -f missing)");
      option.setRequired(false);
      options.addOption(option);

      option = new Option("p", "zkBasePath", true,
          "specify the base path in ZooKeeper for agent configs");
      option.setRequired(false);
      options.addOption(option);

      option = new Option("h", "help", false, "display help text");
      options.addOption(option);

      CommandLineParser parser = new GnuParser();
      CommandLine commandLine = parser.parse(options, args);

      if (commandLine.hasOption('h')) {
        new HelpFormatter().printHelp("flume-ng agent", options, true);
        return;
      }

      String agentName = commandLine.getOptionValue('n');
      boolean reload = !commandLine.hasOption("no-reload-conf");

      if (commandLine.hasOption('z') || commandLine.hasOption("zkConnString")) {
        isZkConfigured = true;
      }

      Application application = null;
      if (isZkConfigured) {
        // get options
        String zkConnectionStr = commandLine.getOptionValue('z');
        String baseZkPath = commandLine.getOptionValue('p');

        if (reload) {
          EventBus eventBus = new EventBus(agentName + "-event-bus");
          List<LifecycleAware> components = Lists.newArrayList();
          PollingZooKeeperConfigurationProvider zookeeperConfigurationProvider =
              new PollingZooKeeperConfigurationProvider(
                  agentName, zkConnectionStr, baseZkPath, eventBus);
          components.add(zookeeperConfigurationProvider);
          application = new Application(components);
          eventBus.register(application);
        } else {
          StaticZooKeeperConfigurationProvider zookeeperConfigurationProvider =
              new StaticZooKeeperConfigurationProvider(
                  agentName, zkConnectionStr, baseZkPath);
          application = new Application();
          application.handleConfigurationEvent(zookeeperConfigurationProvider.getConfiguration());
        }
      } else {
        File configurationFile = new File(commandLine.getOptionValue('f'));
        /*
         * 确保当文件不存在时agent会启动失败
         */
        if (!configurationFile.exists()) {
          // If command line invocation, then need to fail fast
          if (System.getProperty(Constants.SYSPROP_CALLED_FROM_SERVICE) ==
              null) {
            String path = configurationFile.getPath();
            try {
              path = configurationFile.getCanonicalPath();
            } catch (IOException ex) {
              logger.error("Failed to read canonical path for file: " + path,
                  ex);
            }
            throw new ParseException(
                "The specified configuration file does not exist: " + path);
          }
        }
        List<LifecycleAware> components = Lists.newArrayList();

        if (reload) {
          EventBus eventBus = new EventBus(agentName + "-event-bus");
          PollingPropertiesFileConfigurationProvider configurationProvider =
              new PollingPropertiesFileConfigurationProvider(
                  agentName, configurationFile, eventBus, 30);
          components.add(configurationProvider);
          application = new Application(components);
          eventBus.register(application);
        } else {
          PropertiesFileConfigurationProvider configurationProvider =
              new PropertiesFileConfigurationProvider(agentName, configurationFile);
          application = new Application();
          application.handleConfigurationEvent(configurationProvider.getConfiguration());
        }
      }
      application.start();

      final Application appReference = application;
      Runtime.getRuntime().addShutdownHook(new Thread("agent-shutdown-hook") {
        @Override
        public void run() {
          appReference.stop();
        }
      });

    } catch (Exception e) {
      logger.error("A fatal error occurred while running. Exception follows.", e);
    }
  }

  /*启动方法*/
  public synchronized void start() {
    for (LifecycleAware component : components) {
      supervisor.supervise(component,
          new SupervisorPolicy.AlwaysRestartPolicy(), LifecycleState.START);
    }
  }

  /*响应EventBus的方法*/
  @Subscribe
  public synchronized void handleConfigurationEvent(MaterializedConfiguration conf) {
    stopAllComponents();
    startAllComponents(conf);
  }

  /*停止方法*/
  public synchronized void stop() {
    supervisor.stop();
    if (monitorServer != null) {
      monitorServer.stop();
    }
  }

  /*停止所有组件*/
  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();
    }
  }

  /*启动所有组件*/
  private void startAllComponents(MaterializedConfiguration materializedConfiguration) {
    logger.info("Starting new configuration:{}", materializedConfiguration);

    this.materializedConfiguration = materializedConfiguration;
	/*启动Channel*/
    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.
     */
    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);
        }
      }
    }

	/*启动SinkRunner*/
    for (Entry<String, SinkRunner> entry : materializedConfiguration.getSinkRunners().entrySet()) {
      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);
      }
    }
	/*启动SourceRunner*/
    for (Entry<String, SourceRunner> entry :
         materializedConfiguration.getSourceRunners().entrySet()) {
      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();
  }

1）40行：检查Shell命令，如果含有'h'字符则返回帮助命令

2）52行：判断命令行中是否有ZooKeeper相关信息，如果有则获取zookeeper相关信息，通过PollingZooKeeperConfigurationProvider或者StaticZooKeeperConfigurationProvider 去调用存储在zookeeper中的配置信息，如果没有的话则调用PollingPropertiesFileConfigurationProvider或者PropertiesFileConfigurationProvider去指定路径读取配置文件进行加载。

3）57行和96行：无论从zookeeper中还是file中获取配置文件，都需要判断命令行中是否有“no-reload-conf”，根据reload = !commandLine.hasOption("no-reload-conf")获得结果，如果reload为真，那么程序会每隔30秒检查一次配置文件，如果检查到配置文件发生变化则关闭原有组件，重新启动，这部分细节在XXProvider中体现。

4）如果是动态轮询的方式，那么会将application注册到EventBus中，然后调用Application类中的start()来启动components，如果是只加载一次的话，则使用handleConfigurationEvent()来启动。handleConfigurationEvent()同时也是EventBus的回调函数，当eventbus执行post时，该方法就会被调用。

5）所有Application的start()实际上调用了XXProvider中的start()，来执行真正组件的启动。

6）无论是reload还是一次加载，我们可以看到的是都是调用handleConfigurationEvent()来执行，该方法最终是调用stopAllComponents()和startAllComponent来完成的

7）stopAllComponent我们就不说了，重点来看看startAllComponents，它的启动顺序是有讲究的，先启动channels，再启动SinkRunner，最后启动SourceRunner。

这里面有两个问题：

1）启动顺序的问题：为什么要先启动channel，因为sink和source的连接纽带就是channel，而且sink和source的启动都要判断是否存在连接channel，所以channel要先启动，至于sink比source先启动，我认为应该是sink作为最后消费者，而source作为数据来源，那么防止数据堆积在channel中，所以先启动消费者，再启动生产者，需求促进供给嘛，瞎扯的。

2）SourceRunner和SinkRunner是什么玩意，source和sink哪里去了，这里就简单说下，SourceRunner和SinkRunner是用于启动source和sink的驱动类，我们在下一篇source、sink和channel的分析中再来细说

2 XXProvider

该类是启动组件时主要的类，这里就以PollingPropertiesFileConfigurationProvider举例说明，上代码

public class PollingPropertiesFileConfigurationProvider
    extends PropertiesFileConfigurationProvider
    implements LifecycleAware {

  private static final Logger LOGGER =
      LoggerFactory.getLogger(PollingPropertiesFileConfigurationProvider.class);

  private final EventBus eventBus;
  private final File file;
  private final int interval;
  private final CounterGroup counterGroup;
  private LifecycleState lifecycleState;

  private ScheduledExecutorService executorService;

  public PollingPropertiesFileConfigurationProvider(String agentName,
      File file, EventBus eventBus, int interval) {
    super(agentName, file);
    this.eventBus = eventBus;
    this.file = file;
    this.interval = interval;
    counterGroup = new CounterGroup();
    lifecycleState = LifecycleState.IDLE;
  }

  @Override
  public void start() {
    LOGGER.info("Configuration provider starting");

    Preconditions.checkState(file != null,
        "The parameter file must not be null");

    executorService = Executors.newSingleThreadScheduledExecutor(
            new ThreadFactoryBuilder().setNameFormat("conf-file-poller-%d")
                .build());

    FileWatcherRunnable fileWatcherRunnable =
        new FileWatcherRunnable(file, counterGroup);

    executorService.scheduleWithFixedDelay(fileWatcherRunnable, 0, interval,
        TimeUnit.SECONDS);

    lifecycleState = LifecycleState.START;

    LOGGER.debug("Configuration provider started");
  }

  @Override
  public void stop() {
    LOGGER.info("Configuration provider stopping");

    executorService.shutdown();
    try {
      while (!executorService.awaitTermination(500, TimeUnit.MILLISECONDS)) {
        LOGGER.debug("Waiting for file watcher to terminate");
      }
    } catch (InterruptedException e) {
      LOGGER.debug("Interrupted while waiting for file watcher to terminate");
      Thread.currentThread().interrupt();
    }
    lifecycleState = LifecycleState.STOP;
    LOGGER.debug("Configuration provider stopped");
  }

  @Override
  public synchronized  LifecycleState getLifecycleState() {
    return lifecycleState;
  }

  @Override
  public String toString() {
    return "{ file:" + file + " counterGroup:" + counterGroup + "  provider:"
        + getClass().getCanonicalName() + " agentName:" + getAgentName() + " }";
  }

  public class FileWatcherRunnable implements Runnable {

    private final File file;
    private final CounterGroup counterGroup;

    private long lastChange;

    public FileWatcherRunnable(File file, CounterGroup counterGroup) {
      super();
      this.file = file;
      this.counterGroup = counterGroup;
      this.lastChange = 0L;
    }

    @Override
    public void run() {
      LOGGER.debug("Checking file:{} for changes", file);

      counterGroup.incrementAndGet("file.checks");

      long lastModified = file.lastModified();

      if (lastModified > lastChange) {
        LOGGER.info("Reloading configuration file:{}", file);

        counterGroup.incrementAndGet("file.loads");

        lastChange = lastModified;

        try {
          eventBus.post(getConfiguration());
        } catch (Exception e) {
          LOGGER.error("Failed to load configuration data. Exception follows.",
              e);
        } catch (NoClassDefFoundError e) {
          LOGGER.error("Failed to start agent because dependencies were not " +
              "found in classpath. Error follows.", e);
        } catch (Throwable t) {
          // caught because the caller does not handle or log Throwables
          LOGGER.error("Unhandled error", t);
        }
      }
    }
  }

}

1）我们在Application类中看看它的start()

  public synchronized void start() {
    for (LifecycleAware component : components) {
      supervisor.supervise(component,
          new SupervisorPolicy.AlwaysRestartPolicy(), LifecycleState.START);
    }
  }

这里使用supervisor.supervise()来启动component，那么我就不带大家去看LifecycleSupervisor这个类，在这里就告诉大家，这个方法内部还是调用了LifecycleAware的start()来进行启动。既然讲到了LifecycleAware接口，怎么说都得看看代码

@InterfaceAudience.Public
@InterfaceStability.Stable
public interface LifecycleAware {

  public void start();
  public void stop();
  public LifecycleState getLifecycleState();

}

非常简单，就是三个方法，start()、stop()和getLifecycleState，但是flume大多数涉及启动关闭的类都实现了它。

2）我们可以看到PollingPropertiesFileConfigurationProvider也是实现了LifecycleAware接口，那么appliaction的start()实际上就是调用PollingPropertiesFileConfigurationProvider的start()

3）48行：启动了一个30秒执行一次的线程，也就是30秒检查一次配置文件。这个线程是一个内部类FileWatcherRunnable（77行）

4）99行：判断文件是否有改动，如果有则调用eventBus.post(getConfiguration()).那么订阅了事件的Application类则会调用handleConfigurationEvent()执行组件的全部关闭和重启。

5）同时我们注意到该类中是没有getConfiguration()的，该方法是它的父类AbstractConfigurationProvider中定义的，用于获取配置文件信息，这里就不带大家看了，有兴趣可以看一下。

启动流程的分析就到此为止，这里显示不了行号，尴尬