Elasticsearch2.4学习（四）------源码分析之启动过程
本片文章主要分析Elasticsearch2.4的启动过程
一、Elasticsearch类
在源码的org.elasticsearch.bootstrap包中，有Elasticsearch类，该类用于启动Elasticsearch。如下给出这个类的main函数：
public static void main(String[] args) throws StartupError {
try {
Bootstrap.init(args);
} catch (Throwable t) {
// format exceptions to the console in a special way
// to avoid 2MB stacktraces from guice, etc.
throw new StartupError(t);
}
}二、Bootstrap类
从Elasticsearch类的main函数可以看到，启动过程调用了Bootstrap类的init函数。
我们先到org.elasticsearch.bootstrap包中看一看Bootstrap类，有一个宏观了解。
final class Bootstrap {
private static volatile Bootstrap INSTANCE;
private volatile Node node;
private final CountDownLatch keepAliveLatch = new CountDownLatch(1);
private final Thread keepAliveThread;
/** creates a new instance */
Bootstrap() {
keepAliveThread = new Thread(new Runnable() {
@Override
public void run() {
try {
keepAliveLatch.await();
} catch (InterruptedException e) {
// bail out
}
}
}, "elasticsearch[keepAlive/" + Version.CURRENT + "]");
keepAliveThread.setDaemon(false);
// keep this thread alive (non daemon thread) until we shutdown
Runtime.getRuntime().addShutdownHook(new Thread() {
@Override
public void run() {
keepAliveLatch.countDown();
}
});
}
// 后面的代码省略......
}BootStrap类主要包含node、keepAliveLatch、KeepAliveThread这三个实例。
再来看它的构造函数，主要就是实现KeepAliveThread线程的run方法，让这个线程调用keepAliveLatch的await方法，keepAliveLatch初始化为1。当keepAliveLatch没有减到0时，KeepAliveThread线程一直等待，这个线程其实相当于一个HeartBeat，用于表示Elasticsearch是否还活着。
定义完run方法后，将keepAliveThread设置为用户线程。
注意：此时KeepAliveThread只是定义好了，还没有start。
最后，加了一个关闭钩子，在JVM关闭之前，需要执行addShutdownHook中定义的线程的run方法。即执行keepAliveLatch的countDown方法，这时KeepAliveThread得以向后面执行，最终退出。具体内容可以参考Runtime.getRuntime().addShutdownHook关闭钩子介绍
三、Bootstrap类的init函数
/**
* This method is invoked by {@link Elasticsearch#main(String[])}
* to startup elasticsearch.
*/
static void init(String[] args) throws Throwable {
// Set the system property before anything has a chance to trigger its use
// 设置系统属性
System.setProperty("es.logger.prefix", "");
BootstrapCLIParser bootstrapCLIParser = new BootstrapCLIParser();
CliTool.ExitStatus status = bootstrapCLIParser.execute(args);
if (CliTool.ExitStatus.OK != status) {
exit(status.status());
}
// 创建Bootstrap实例
INSTANCE = new Bootstrap();
boolean foreground = !"false".equals(System.getProperty("es.foreground",
System.getProperty("es-foreground")));
// handle the wrapper system property, if its a service, don't run as a service
if (System.getProperty("wrapper.service", "XXX").equalsIgnoreCase("true")) {
foreground = false;
}
// 获取运行时环境
Environment environment = initialSettings(foreground);
// 从运行时环境获取配置
Settings settings = environment.settings();
LogConfigurator.configure(settings, true);
checkForCustomConfFile();
// 创建pid文件
if (environment.pidFile() != null) {
PidFile.create(environment.pidFile(), true);
}
// 如果设置了打开文件个数的上限，则打印相应的log信息
if (System.getProperty("es.max-open-files", "false").equals("true")) {
ESLogger logger = Loggers.getLogger(Bootstrap.class);
logger.info("max_open_files [{}]",
ProcessProbe.getInstance().getMaxFileDescriptorCount());
}
// warn if running using the client VM
// 如果启动时是HotSpot的Client VM，则打印log信息，提醒采用Sever VM，以获得更好的性能
if (JvmInfo.jvmInfo().getVmName().toLowerCase(Locale.ROOT).contains("client")) {
ESLogger logger = Loggers.getLogger(Bootstrap.class);
logger.warn("jvm uses the client vm, make sure to run `java` with the
server vm for best performance by adding `-server` to the
command line");
}
try {
if (!foreground) {
// 如果foreground是false则不打印日志，关闭系统输出
Loggers.disableConsoleLogging();
closeSystOut();
}
// fail if using broken version
// 检测JVM的版本
JVMCheck.check();
INSTANCE.setup(true, settings, environment);
INSTANCE.start();
if (!foreground) {
closeSysError();
}
} catch (Throwable e) {
// 省略异常处理部分代码......
}
}以上代码中已经添加了详细的注释，按照先后顺序，主要是做了如下几件事情：
1、设置系统属性
2、获取BootStrap的实例INSTANCE
3、获取运行环境、创建pid文件
4、判断是否设置了打开文件的最大个数、判断是否以Client VM的方式启动了VM（具体内容可以参考JVM的Client VM 与 Server VM介绍），并打印相应log信息
5、判断是否打印系统日志
6、检测JVM版本
7、INSTANCE执行setup
8、INSTANCE执行start
如下我们针对setup和start两个过程进行详细说明。
四、Bootstrap类的setup函数
private void setup(boolean addShutdownHook, Settings settings,
Environment environment) throws Exception {
final ESLogger logger = Loggers.getLogger(Bootstrap.class);
final DeprecationLogger deprecationLogger = new DeprecationLogger(logger);
// 获取bootstrap.mlockall的配置信息
final Boolean mlockall = settings.getAsBoolean("bootstrap.mlockall", null);
if (mlockall != null) {
// 如果配置了，则在过时日志中添加信息，提醒该配置项已经过时
deprecationLogger.deprecated("setting [bootstrap.mlockall] is deprecated;
use [bootstrap.memory_lock]");
}
// 获取bootstrap.memory_lock配置信息
final Boolean memoryLock = settings.getAsBoolean("bootstrap.memory_lock", null);
// both bootstrap.mlockall and bootstrap.memory_lock are set, refuse to start
if (mlockall != null && memoryLock != null) {
// 如果对bootstrap.mlockall和bootstrap.memory_lock都进行了配置则抛出异常
throw new IllegalArgumentException("both [bootstrap.mlockall] and
[bootstrap.memory_lock] configured,"
+ " just use [bootstrap.memory_lock]");
}
// 本地初始化
initializeNatives(environment.tmpFile(),
memoryLock != null ? memoryLock : mlockall != null ? mlockall : false,
settings.getAsBoolean("bootstrap.seccomp", true),
settings.getAsBoolean("bootstrap.ctrlhandler", true));
// initialize probes before the security manager is installed
initializeProbes();
if (addShutdownHook) {
// 添加关闭钩子，在VM关闭之前先关闭node
Runtime.getRuntime().addShutdownHook(new Thread() {
@Override
public void run() {
if (node != null) {
node.close();
}
}
});
}
// look for jar hell
// 查询JatHell(打印classpath等信息)
JarHell.checkJarHell();
// install SM after natives, shutdown hooks, etc.
setupSecurity(settings, environment);
Settings nodeSettings = Settings.settingsBuilder()
.put(settings)
.put(InternalSettingsPreparer.IGNORE_SYSTEM_PROPERTIES_SETTING, true)
.build();
// build node
NodeBuilder nodeBuilder = NodeBuilder.nodeBuilder().settings(nodeSettings);
node = nodeBuilder.build();
}1、检测bootstrap.mlockall和bootstrap.memory_lock信息，并打印相应log信息
2、本地初始化（检测是否为root用户启动、设置安全计算模式、对内存进行加锁、监听来自ctrl键的关闭事件）
3、初始化两种probes，分别是ProcessProbe和Osprobe，这两个probe将会提供给ES的stats api所需要的一些ES进程和OS层面的信息
3、添加关闭钩子，在VM关闭之前，关闭node
4、查询JarHell（打印classpath等信息）
5、安装security manager（SM）
6、build node
本地初始化的代码实现的功能在2中已经说明，代码就不展开了。下面说明build node的过程。
五、Node类的构造函数
我们先来看org.elasticsearch.node包中的NodeBuilder类的nodeBuilder.build()函数（ 只进行build不进行start）/**
* Builds the node without starting it.
*/
public Node build() {
return new Node(settings.build());
}public class Node implements Releasable {
private static final String CLIENT_TYPE = "node";
public static final String HTTP_ENABLED = "http.enabled";
private final Lifecycle lifecycle = new Lifecycle();
private final Injector injector;
private final Settings settings;
private final Environment environment;
private final PluginsService pluginsService;
private final Client client;
/**
* Constructs a node with the given settings.
*
* @param preparedSettings Base settings to configure the node with
*/
public Node(Settings preparedSettings) {
// 调用带参构造函数
this(InternalSettingsPreparer.prepareEnvironment(preparedSettings, null),
Version.CURRENT, Collections.>emptyList());
}
protected Node(Environment tmpEnv, Version version,
Collection> classpathPlugins) {
// 省略部分代码......
logger.info("initializing ...");
// 省略部分代码......
boolean success = false;
try {
ModulesBuilder modules = new ModulesBuilder();
modules.add(new Version.Module(version));
modules.add(new CircuitBreakerModule(settings));
for (Module pluginModule : pluginsService.nodeModules()) {
modules.add(pluginModule);
}
modules.add(new PluginsModule(pluginsService));
modules.add(new SettingsModule(this.settings));
modules.add(new NodeModule(this));
modules.add(new NetworkModule(namedWriteableRegistry));
modules.add(new ScriptModule(this.settings));
modules.add(new EnvironmentModule(environment));
modules.add(new NodeEnvironmentModule(nodeEnvironment));
modules.add(new ClusterNameModule(this.settings));
modules.add(new ThreadPoolModule(threadPool));
modules.add(new DiscoveryModule(this.settings));
modules.add(new ClusterModule(this.settings));
modules.add(new RestModule(this.settings));
modules.add(new TransportModule(settings, namedWriteableRegistry));
if (settings.getAsBoolean(HTTP_ENABLED, true)) {
modules.add(new HttpServerModule(settings));
}
modules.add(new IndicesModule());
modules.add(new SearchModule());
modules.add(new ActionModule(false));
modules.add(new MonitorModule(settings));
modules.add(new GatewayModule(settings));
modules.add(new NodeClientModule());
modules.add(new ShapeModule());
modules.add(new PercolatorModule());
modules.add(new ResourceWatcherModule());
modules.add(new RepositoriesModule());
modules.add(new TribeModule());
pluginsService.processModules(modules);
injector = modules.createInjector();
// 省略部分代码......
success = true;
} finally {
// 省略部分代码......
}
logger.info("initialized");
}
} 这里有必要简单介绍下Guice，不然看到这里好多人会看不懂。Guice是google开源的一个依赖注入的框架，比起spring更加的轻量级，关键点：
1、使用@injectguice会扫描inject注释，并对方法中出现的参数实例寻找对应注册的实例进行初始化。
2、bind接口将接口跟具体实现类绑定。
3、使用 Injector 引导应用程序。
因此可以看到每个module里面都有一个方法configure()用于将对象和实现类作绑定。
至此，INSTANCE.setup的过程已经解释清楚。
六、Bootstrap类的start函数
private void start() {
node.start();
keepAliveThread.start();
}其中，keepAliveThread线程会在Elasticsearch退出之前一直等待着keepAliveLatch减为0。我们看看node.start函数做了哪些事情。
七、Node类的start函数
/**
* Start the node. If the node is already started, this method is no-op.
*/
public Node start() {
// 如果node已经启动，则直接返回
if (!lifecycle.moveToStarted()) {
return this;
}
ESLogger logger = Loggers.getLogger(Node.class, settings.get("name"));
logger.info("starting ...");
// hack around dependency injection problem (for now...)
injector.getInstance(Discovery.class).setRoutingService(
injector.getInstance(RoutingService.class));
for (Class plugin : pluginsService.nodeServices()) {
injector.getInstance(plugin).start();
}
injector.getInstance(MappingUpdatedAction.class).setClient(client);
injector.getInstance(IndicesService.class).start();
injector.getInstance(IndexingMemoryController.class).start();
injector.getInstance(IndicesClusterStateService.class).start();
injector.getInstance(IndicesTTLService.class).start();
injector.getInstance(SnapshotsService.class).start();
injector.getInstance(SnapshotShardsService.class).start();
injector.getInstance(RoutingService.class).start();
injector.getInstance(SearchService.class).start();
injector.getInstance(MonitorService.class).start();
injector.getInstance(RestController.class).start();
// TODO hack around circular dependencies problems
injector.getInstance(GatewayAllocator.class).setReallocation(
injector.getInstance(ClusterService.class),
injector.getInstance(RoutingService.class));
injector.getInstance(ResourceWatcherService.class).start();
injector.getInstance(GatewayService.class).start();
// Start the transport service now so the publish address will be
// added to the local disco node in ClusterService
TransportService transportService = injector.getInstance(TransportService.class);
transportService.start();
injector.getInstance(ClusterService.class).start();
// 省略部分代码......
transportService.acceptIncomingRequests();
discoService.joinClusterAndWaitForInitialState();
if (settings.getAsBoolean("http.enabled", true)) {
injector.getInstance(HttpServer.class).start();
}
injector.getInstance(TribeService.class).start();
if (settings.getAsBoolean("node.portsfile", false)) {
if (settings.getAsBoolean("http.enabled", true)) {
HttpServerTransport http = injector.getInstance(HttpServerTransport.class);
writePortsFile("http", http.boundAddress());
}
TransportService transport = injector.getInstance(TransportService.class);
writePortsFile("transport", transport.boundAddress());
}
logger.info("started");
return this;
}到目前为止，整个Elasticsearch的启动就已经完成。