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