TOMCAT源码分析-生命周期管理

开篇

 这篇文章参考文末提及的文章，主要在于想讲解清楚容器的初始化和启动过程，当然也以此文纪念我稍显遗憾的双十一。

TOMCAT容器组成

说明：

• StandardServer、StandardService、Connector、StandardContext这些容器，彼此之间都有父子关系，每个容器都可能包含零个或者多个子容器，这些子容器可能存在不同类型或者相同类型的多个。

TOMCAT生命周期类接口设计

说明：

• 在一个Tomcat的StandardService当中包括StandardEngine、StandardHost、StandardContext、StandardWrapper，统一继承自ContainerBase类。
• Lifecycle：定义了容器生命周期、容器状态转换及容器状态迁移事件的监听器注册和移除等主要接口；
• LifecycleBase：作为Lifecycle接口的抽象实现类，运用抽象模板模式将所有容器的生命周期及状态转换衔接起来，此外还提供了生成LifecycleEvent事件的接口；
• LifecycleSupport：提供有关LifecycleEvent事件的监听器注册、移除，并且使用经典的监听器模式，实现事件生成后触打监听器的实现；
• MBeanRegistration：Java jmx框架提供的注册MBean的接口，引入此接口是为了便于使用JMX提供的管理功能；
• LifecycleMBeanBase：Tomcat提供的对MBeanRegistration的抽象实现类，运用抽象模板模式将所有容器统一注册到JMX；

TOMCAT容器状态

目前，Tomcat的容器具有以下状态：

• NEW：容器刚刚创建时，即在LifecycleBase实例构造完成时的状态。
• INITIALIZED：容器初始化完成时的状态。
• STARTING_PREP：容器启动前的状态。
• STARTING：容器启动过程中的状态。
• STARTED：容器启动完成的状态。
• STOPPING_PREP：容器停止前的状态。
• STOPPING：容器停止过程中的状态。
• STOPPED：容器停止完成的状态。
• DESTROYED：容器销毁后的状态。
• FAILED：容器启动、停止过程中出现异常的状态。
• MUST_STOP：此状态未使用。
• MUST_DESTROY：此状态未使用。

public enum LifecycleState {
    NEW(false, null),
    INITIALIZING(false, Lifecycle.BEFORE_INIT_EVENT),
    INITIALIZED(false, Lifecycle.AFTER_INIT_EVENT),
    STARTING_PREP(false, Lifecycle.BEFORE_START_EVENT),
    STARTING(true, Lifecycle.START_EVENT),
    STARTED(true, Lifecycle.AFTER_START_EVENT),
    STOPPING_PREP(true, Lifecycle.BEFORE_STOP_EVENT),
    STOPPING(false, Lifecycle.STOP_EVENT),
    STOPPED(false, Lifecycle.AFTER_STOP_EVENT),
    DESTROYING(false, Lifecycle.BEFORE_DESTROY_EVENT),
    DESTROYED(false, Lifecycle.AFTER_DESTROY_EVENT),
    FAILED(false, null);
}


public interface Lifecycle {
    public static final String BEFORE_INIT_EVENT = "before_init";
    public static final String AFTER_INIT_EVENT = "after_init";
    public static final String START_EVENT = "start";
    public static final String BEFORE_START_EVENT = "before_start";
    public static final String AFTER_START_EVENT = "after_start";
    public static final String STOP_EVENT = "stop";
    public static final String BEFORE_STOP_EVENT = "before_stop";
    public static final String AFTER_STOP_EVENT = "after_stop";
    public static final String AFTER_DESTROY_EVENT = "after_destroy";
    public static final String BEFORE_DESTROY_EVENT = "before_destroy";
    public static final String PERIODIC_EVENT = "periodic";
    public static final String CONFIGURE_START_EVENT = "configure_start";
    public static final String CONFIGURE_STOP_EVENT = "configure_stop";
}

Tomcat状态转移图

 *            start()
 *  -----------------------------
 *  |                           |
 *  | init()                    |
 * NEW -»-- INITIALIZING        |
 * | |           |              |     ------------------«-----------------------
 * | |           |auto          |     |                                        |
 * | |          \|/    start() \|/   \|/     auto          auto         stop() |
 * | |      INITIALIZED --»-- STARTING_PREP --»- STARTING --»- STARTED --»---  |
 * | |         |                                                            |  |
 * | |destroy()|                                                            |  |
 * | --»-----«--    ------------------------«--------------------------------  ^
 * |     |          |                                                          |
 * |     |         \|/          auto                 auto              start() |
 * |     |     STOPPING_PREP ----»---- STOPPING ------»----- STOPPED -----»-----
 * |    \|/                               ^                     |  ^
 * |     |               stop()           |                     |  |
 * |     |       --------------------------                     |  |
 * |     |       |                                              |  |
 * |     |       |    destroy()                       destroy() |  |
 * |     |    FAILED ----»------ DESTROYING ---«-----------------  |
 * |     |                        ^     |                          |
 * |     |     destroy()          |     |auto                      |
 * |     --------»-----------------    \|/                         |
 * |                                 DESTROYED                     |
 * |                                                               |
 * |                            stop()                             |
 * ----»-----------------------------»------------------------------
 *

容器的生命周期

每个容器都会有自身的生命周期，其中也涉及状态的迁移，以及伴随的事件生成。所有容器的转态转换（如新建、初始化、启动、停止等）都是由外到内，由上到下进行，即先执行父容器的状态转换及相关操作，然后再执行子容器的转态转换，这个过程是层层迭代执行的。

1、容器新建

public abstract class LifecycleBase implements Lifecycle {
    private volatile LifecycleState state = LifecycleState.NEW;
}

2、容器初始化

说明：

• 1、调用方调用容器父类LifecycleBase的init方法，LifecycleBase的init方法主要完成一些所有容器公共抽象出来的动作；
• 2、LifecycleBase的init方法调用具体容器的initInternal方法实现，此initInternal方法用于对容器本身真正的初始化；
• 3、具体容器的initInternal方法调用父类LifecycleMBeanBase的initInternal方法实现，此initInternal方法用于将容器托管到JMX，便于运维管理；
• 4、LifecycleMBeanBase的initInternal方法调用自身的register方法，将容器作为MBean注册到MBeanServer；
• 5、容器如果有子容器，会调用子容器的init方法；
• 6、容器初始化完毕，LifecycleBase会将容器的状态更改为初始化完毕，即LifecycleState.INITIALIZED。

源码部分

• 容器初始化的时候调用init方法最终执行的是LifecycleBase的init()方法。
• init()过程经历容器状态变化，经历NEW-> INITIALIZING-> INITIALIZED状态转移。
• init()内部的initInternal()在会调用容器本身的实现的initInternal()方法。

public abstract class LifecycleBase implements Lifecycle {

    public final synchronized void init() throws LifecycleException {
        if (!state.equals(LifecycleState.NEW)) {
            invalidTransition(Lifecycle.BEFORE_INIT_EVENT);
        }

        try {
            setStateInternal(LifecycleState.INITIALIZING, null, false);
            initInternal();
            setStateInternal(LifecycleState.INITIALIZED, null, false);
        } catch (Throwable t) {
            ExceptionUtils.handleThrowable(t);
            setStateInternal(LifecycleState.FAILED, null, false);
            throw new LifecycleException(
                    sm.getString("lifecycleBase.initFail",toString()), t);
        }
    }

    protected abstract void initInternal() throws LifecycleException;
}

以StandardServer为例

• 1、StandardServer的initInternal()调用父类LifecycleMBeanBase的initInternal()方法。
• 2、StandardServer的initInternal()方法调用services[i].init()初始化子容器。

public final class StandardServer extends LifecycleMBeanBase implements Server {

    protected void initInternal() throws LifecycleException {

        super.initInternal();

        // Register global String cache
        // Note although the cache is global, if there are multiple Servers
        // present in the JVM (may happen when embedding) then the same cache
        // will be registered under multiple names
        onameStringCache = register(new StringCache(), "type=StringCache");

        // Register the MBeanFactory
        MBeanFactory factory = new MBeanFactory();
        factory.setContainer(this);
        onameMBeanFactory = register(factory, "type=MBeanFactory");

        // Register the naming resources
        globalNamingResources.init();

        // Populate the extension validator with JARs from common and shared
        // class loaders
        if (getCatalina() != null) {
            ClassLoader cl = getCatalina().getParentClassLoader();
            // Walk the class loader hierarchy. Stop at the system class loader.
            // This will add the shared (if present) and common class loaders
            while (cl != null && cl != ClassLoader.getSystemClassLoader()) {
                if (cl instanceof URLClassLoader) {
                    URL[] urls = ((URLClassLoader) cl).getURLs();
                    for (URL url : urls) {
                        if (url.getProtocol().equals("file")) {
                            try {
                                File f = new File (url.toURI());
                                if (f.isFile() &&
                                        f.getName().endsWith(".jar")) {
                                    ExtensionValidator.addSystemResource(f);
                                }
                            } catch (URISyntaxException e) {
                                // Ignore
                            } catch (IOException e) {
                                // Ignore
                            }
                        }
                    }
                }
                cl = cl.getParent();
            }
        }
        // Initialize our defined Services
        for (int i = 0; i < services.length; i++) {
            services[i].init();
        }
    }
}



public abstract class LifecycleMBeanBase extends LifecycleBase
        implements JmxEnabled {

    protected void initInternal() throws LifecycleException {

        // If oname is not null then registration has already happened via
        // preRegister().
        if (oname == null) {
            mserver = Registry.getRegistry(null, null).getMBeanServer();

            oname = register(this, getObjectNameKeyProperties());
        }
    }
}

以StandardContext为例

• 1、StandardContext的initInternal()方法调用父类ContainerBase的initInternal()方法。
• 2、ContainerBase的initInternal()方法实现线程池的创建，并调用父类LifecycleMBeanBase的initInternal()方法。
• 3、StandardEngine、StandardHost、StandardContext、StandardWrapper容器都是如此。

public class StandardContext extends ContainerBase
        implements Context, NotificationEmitter {

    protected void initInternal() throws LifecycleException {
        super.initInternal();

        // Register the naming resources
        if (namingResources != null) {
            namingResources.init();
        }

        // Send j2ee.object.created notification
        if (this.getObjectName() != null) {
            Notification notification = new Notification("j2ee.object.created",
                    this.getObjectName(), sequenceNumber.getAndIncrement());
            broadcaster.sendNotification(notification);
        }
    }
}



public abstract class ContainerBase extends LifecycleMBeanBase
        implements Container {

    @Override
    protected void initInternal() throws LifecycleException {
        BlockingQueue<Runnable> startStopQueue = new LinkedBlockingQueue<>();
        startStopExecutor = new ThreadPoolExecutor(
                getStartStopThreadsInternal(),
                getStartStopThreadsInternal(), 10, TimeUnit.SECONDS,
                startStopQueue,
                new StartStopThreadFactory(getName() + "-startStop-"));
        startStopExecutor.allowCoreThreadTimeOut(true);
        super.initInternal();
    }
}



public abstract class LifecycleMBeanBase extends LifecycleBase
        implements JmxEnabled {

    protected void initInternal() throws LifecycleException {

        // If oname is not null then registration has already happened via
        // preRegister().
        if (oname == null) {
            mserver = Registry.getRegistry(null, null).getMBeanServer();

            oname = register(this, getObjectNameKeyProperties());
        }
    }
}

3、容器启动

说明：

• 1、调用方调用容器父类LifecycleBase的start方法，LifecycleBase的start方法主要完成一些所有容器公共抽象出来的动作；
• 2、LifecycleBase的start方法先将容器状态改为LifecycleState.STARTING_PREP，然后调用具体容器的startInternal方法实现，此startInternal方法用于对容器本身真正的初始化；
• 3、具体容器的startInternal方法会将容器状态改为LifecycleState.STARTING，容器如果有子容器，会调用子容器的start方法启动子容器；
• 4、容器启动完毕，LifecycleBase会将容器的状态更改为启动完毕，即LifecycleState.STARTED。

源码部分

• 1、如果当前容器已经处于启动过程（即容器状态为LifecycleState.STARTING_PREP、LifecycleState.STARTING、LifecycleState.STARTED）中，则会产生并且用日志记录LifecycleException异常并退出。
• 2、如果容器依然处于LifecycleState.NEW状态，则在启动之前，首先确保初始化完毕。
• 3、LifecycleBase的start()方法内部通过startInternal()启动容器。

public abstract class LifecycleBase implements Lifecycle {

    public final synchronized void start() throws LifecycleException {

        if (LifecycleState.STARTING_PREP.equals(state) || LifecycleState.STARTING.equals(state) ||
                LifecycleState.STARTED.equals(state)) {

            if (log.isDebugEnabled()) {
                Exception e = new LifecycleException();
                log.debug(sm.getString("lifecycleBase.alreadyStarted", toString()), e);
            } else if (log.isInfoEnabled()) {
                log.info(sm.getString("lifecycleBase.alreadyStarted", toString()));
            }

            return;
        }

        if (state.equals(LifecycleState.NEW)) {
            init();
        } else if (state.equals(LifecycleState.FAILED)) {
            stop();
        } else if (!state.equals(LifecycleState.INITIALIZED) &&
                !state.equals(LifecycleState.STOPPED)) {
            invalidTransition(Lifecycle.BEFORE_START_EVENT);
        }

        try {
            setStateInternal(LifecycleState.STARTING_PREP, null, false);
            startInternal();
            if (state.equals(LifecycleState.FAILED)) {
                // This is a 'controlled' failure. The component put itself into the
                // FAILED state so call stop() to complete the clean-up.
                stop();
            } else if (!state.equals(LifecycleState.STARTING)) {
                // Shouldn't be necessary but acts as a check that sub-classes are
                // doing what they are supposed to.
                invalidTransition(Lifecycle.AFTER_START_EVENT);
            } else {
                setStateInternal(LifecycleState.STARTED, null, false);
            }
        } catch (Throwable t) {
            // This is an 'uncontrolled' failure so put the component into the
            // FAILED state and throw an exception.
            ExceptionUtils.handleThrowable(t);
            setStateInternal(LifecycleState.FAILED, null, false);
            throw new LifecycleException(sm.getString("lifecycleBase.startFail", toString()), t);
        }
    }
}

以StandardServer为例

• 1、产生CONFIGURE_START_EVENT事件；
• 2、将自身状态更改为LifecycleState.STARTING；
• 3、调用子容器Service（默认为StandardService）的start方法启动子容器。

public final class StandardServer extends LifecycleMBeanBase implements Server {

    protected void startInternal() throws LifecycleException {

        fireLifecycleEvent(CONFIGURE_START_EVENT, null);
        setState(LifecycleState.STARTING);

        globalNamingResources.start();

        // Start our defined Services
        synchronized (servicesLock) {
            for (int i = 0; i < services.length; i++) {
                services[i].start();
            }
        }
    }
}


public abstract class LifecycleMBeanBase extends LifecycleBase
        implements JmxEnabled { }


public abstract class LifecycleBase implements Lifecycle {
    protected abstract void startInternal() throws LifecycleException;
}

以StandardEngine为例

• 1、StandardEngine的startInternal()方法调用父类ContainerBase的startInternal()方法。
• 2、ContainerBase类的startInternal()方法线程池来启动子容器startStopExecutor.submit(new StartChild(children[i]))。

public class StandardEngine extends ContainerBase implements Engine {

    protected synchronized void startInternal() throws LifecycleException {

        // Log our server identification information
        if(log.isInfoEnabled())
            log.info( "Starting Servlet Engine: " + ServerInfo.getServerInfo());

        // Standard container startup
        super.startInternal();
    }
}




public abstract class ContainerBase extends LifecycleMBeanBase
        implements Container {

    protected synchronized void startInternal() throws LifecycleException {

        // Start our subordinate components, if any
        logger = null;
        getLogger();
        Cluster cluster = getClusterInternal();
        if (cluster instanceof Lifecycle) {
            ((Lifecycle) cluster).start();
        }
        Realm realm = getRealmInternal();
        if (realm instanceof Lifecycle) {
            ((Lifecycle) realm).start();
        }

        // Start our child containers, if any
        Container children[] = findChildren();
        List<Future<Void>> results = new ArrayList<>();
        for (int i = 0; i < children.length; i++) {
            results.add(startStopExecutor.submit(new StartChild(children[i])));
        }

        MultiThrowable multiThrowable = new MultiThrowable();

        for (Future<Void> result : results) {
            try {
                result.get();
            } catch (Throwable e) {
                log.error(sm.getString("containerBase.threadedStartFailed"), e);
                multiThrowable.add(e);
            }

        }
        if (multiThrowable.size() > 0) {
            throw new LifecycleException(sm.getString("containerBase.threadedStartFailed"),
                    multiThrowable.getThrowable());
        }

        // Start the Valves in our pipeline (including the basic), if any
        if (pipeline instanceof Lifecycle) {
            ((Lifecycle) pipeline).start();
        }


        setState(LifecycleState.STARTING);

        // Start our thread
        threadStart();
    }
}

参考

TOMCAT源码分析——生命周期管理

自我寄语

 很遗憾的双十一，没能稳定的度过，稍显遗憾。