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Tomcat源码分析 -- 3

Tomcat源码分析 -- 3

作者: sschrodinger | 来源:发表于2019-03-07 14:54 被阅读0次

    Tomcat源码分析 -- 3

    sschrodinger

    2018/12/19

    参考

    • 《深入剖析 Tomcat》 - 基于Tomcat 4.x
    • 《Tomcat 架构解析》刘光瑞 著
    • 《大话设计模式》程杰 著
    • Tomcat 8.5.x 源码

    tomcat 生命周期

    如下图所示，tomcat 组件的生命周期有如下的转换方式。

    tomcat 生命周期

    tomcat 生命周期定义在枚举类型LifecycleState中，定义如下：

    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);

    private final boolean available;
    private final String lifecycleEvent;

    private LifecycleState(boolean available, String lifecycleEvent) {
        this.available = available;
        this.lifecycleEvent = lifecycleEvent;
    }

    public boolean isAvailable() {
        return available;
    }

    public String getLifecycleEvent() {
        return lifecycleEvent;
    }
}

    note

    • 枚举的第一个参数代表改组件是否可用
    • 枚举的第二个参数代表生命周期事件

    在 tomcat 中，所有的组件都有父接口Lifecycle，接口相关定义如下：

    public interface Lifecycle {


    // ...
    // ...
    public void init() throws LifecycleException;

    public void start() throws LifecycleException;

    public void stop() throws LifecycleException;

    public void destroy() throws LifecycleException;

    public LifecycleState getState();

    public String getStateName();
    
    //...
}

    tomcat 使用LifecycleBase这个抽象类来实现状态的转换函数，所有的组件不直接继承于lifecycle，而是直接继承于lifecycleBase这个抽象类。抽象类部分代码如下：

    ublic abstract class LifecycleBase implements Lifecycle {

    private volatile LifecycleState state = LifecycleState.NEW;

    @Override
    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;

    @Override
    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);
        }
    }

    @Override
    public final synchronized void stop() throws LifecycleException {

        if (LifecycleState.STOPPING_PREP.equals(state) || LifecycleState.STOPPING.equals(state) ||
                LifecycleState.STOPPED.equals(state)) {

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

            return;
        }

        if (state.equals(LifecycleState.NEW)) {
            state = LifecycleState.STOPPED;
            return;
        }

        if (!state.equals(LifecycleState.STARTED) && !state.equals(LifecycleState.FAILED)) {
            invalidTransition(Lifecycle.BEFORE_STOP_EVENT);
        }

        try {
            if (state.equals(LifecycleState.FAILED)) {
                // Don't transition to STOPPING_PREP as that would briefly mark the
                // component as available but do ensure the BEFORE_STOP_EVENT is
                // fired
                fireLifecycleEvent(BEFORE_STOP_EVENT, null);
            } else {
                setStateInternal(LifecycleState.STOPPING_PREP, null, false);
            }

            stopInternal();

            // Shouldn't be necessary but acts as a check that sub-classes are
            // doing what they are supposed to.
            if (!state.equals(LifecycleState.STOPPING) && !state.equals(LifecycleState.FAILED)) {
                invalidTransition(Lifecycle.AFTER_STOP_EVENT);
            }

            setStateInternal(LifecycleState.STOPPED, null, false);
        } catch (Throwable t) {
            ExceptionUtils.handleThrowable(t);
            setStateInternal(LifecycleState.FAILED, null, false);
            throw new LifecycleException(sm.getString("lifecycleBase.stopFail",toString()), t);
        } finally {
            if (this instanceof Lifecycle.SingleUse) {
                // Complete stop process first
                setStateInternal(LifecycleState.STOPPED, null, false);
                destroy();
            }
        }
    }

    protected abstract void stopInternal() throws LifecycleException;

    @Override
    public final synchronized void destroy() throws LifecycleException {
        if (LifecycleState.FAILED.equals(state)) {
            try {
                // Triggers clean-up
                stop();
            } catch (LifecycleException e) {
                // Just log. Still want to destroy.
                log.warn(sm.getString(
                        "lifecycleBase.destroyStopFail", toString()), e);
            }
        }

        if (LifecycleState.DESTROYING.equals(state) ||
                LifecycleState.DESTROYED.equals(state)) {

            if (log.isDebugEnabled()) {
                Exception e = new LifecycleException();
                log.debug(sm.getString("lifecycleBase.alreadyDestroyed", toString()), e);
            } else if (log.isInfoEnabled() && !(this instanceof Lifecycle.SingleUse)) {
                // Rather than have every component that might need to call
                // destroy() check for SingleUse, don't log an info message if
                // multiple calls are made to destroy()
                log.info(sm.getString("lifecycleBase.alreadyDestroyed", toString()));
            }

            return;
        }

        if (!state.equals(LifecycleState.STOPPED) &&
                !state.equals(LifecycleState.FAILED) &&
                !state.equals(LifecycleState.NEW) &&
                !state.equals(LifecycleState.INITIALIZED)) {
            invalidTransition(Lifecycle.BEFORE_DESTROY_EVENT);
        }

        try {
            setStateInternal(LifecycleState.DESTROYING, null, false);
            destroyInternal();
            setStateInternal(LifecycleState.DESTROYED, null, false);
        } catch (Throwable t) {
            ExceptionUtils.handleThrowable(t);
            setStateInternal(LifecycleState.FAILED, null, false);
            throw new LifecycleException(
                    sm.getString("lifecycleBase.destroyFail",toString()), t);
        }
    }


    protected abstract void destroyInternal() throws LifecycleException;

    @Override
    public LifecycleState getState() {
        return state;
    }

    @Override
    public String getStateName() {
        return getState().toString();
    }

    protected synchronized void setState(LifecycleState state)
            throws LifecycleException {
        setStateInternal(state, null, true);
    }

    protected synchronized void setState(LifecycleState state, Object data)
            throws LifecycleException {
        setStateInternal(state, data, true);
    }

    private synchronized void setStateInternal(LifecycleState state,
            Object data, boolean check) throws LifecycleException {

        if (log.isDebugEnabled()) {
            log.debug(sm.getString("lifecycleBase.setState", this, state));
        }

        if (check) {
            // Must have been triggered by one of the abstract methods (assume
            // code in this class is correct)
            // null is never a valid state
            if (state == null) {
                invalidTransition("null");
                // Unreachable code - here to stop eclipse complaining about
                // a possible NPE further down the method
                return;
            }

            // Any method can transition to failed
            // startInternal() permits STARTING_PREP to STARTING
            // stopInternal() permits STOPPING_PREP to STOPPING and FAILED to
            // STOPPING
            if (!(state == LifecycleState.FAILED ||
                    (this.state == LifecycleState.STARTING_PREP &&
                            state == LifecycleState.STARTING) ||
                    (this.state == LifecycleState.STOPPING_PREP &&
                            state == LifecycleState.STOPPING) ||
                    (this.state == LifecycleState.FAILED &&
                            state == LifecycleState.STOPPING))) {
                // No other transition permitted
                invalidTransition(state.name());
            }
        }

        this.state = state;
        String lifecycleEvent = state.getLifecycleEvent();
        if (lifecycleEvent != null) {
            fireLifecycleEvent(lifecycleEvent, data);
        }
    }

    private void invalidTransition(String type) throws LifecycleException {
        String msg = sm.getString("lifecycleBase.invalidTransition", type,
                toString(), state);
        throw new LifecycleException(msg);
    }
}

    代码冗长，但是实现功能简单，实现了一个类似于有限状态自动机的转换逻辑。

    从init()函数入手，首先检查当前组件状态，如果状态不为 LifecycleState.NEW，则抛出一个错误，否则，将当前状态更新为LifecycleState.INITIALIZING，并且执行抽象函数initInternal()，完成抽象函数的执行后，将当前状态更新为LifecycleState.INITIALIZED。

    start()，stop()，desdroy()函数和init()函数使用流程基本相似，但是应用逻辑更加复杂。同时引入了startInternal()，stopInternal()，desdroyInternal()三个方法以供重写。

    所以，lifecyleBase类，实现了模板方法模式，组件只需要重写initInternal()，startInternal()，stopInternal()，desdroyInternal()四个方法，来完成具体的步骤，比如说数据库初始化等操作。

    举个例子，我们知道 tomcat 组件可以实现父组件启动，就启动所有子组件的功能，同时也可以执行后台程序，这些所有的逻辑程序都在组件的父类型ContainerBase中实现，关键代码如下：

    public abstract class ContainerBase extends LifecycleMBeanBase  implements Container {

    //保存子组件
    protected final HashMap<String, Container> children = new HashMap<>();

    //后台执行间隔事件，-1代表不执行
    protected int backgroundProcessorDelay = -1;
    
    //后台程序线程
    private Thread thread = null;
    
    //组件执行线程
    protected ThreadPoolExecutor startStopExecutor;
    
    @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();
    }
    
    @Override
    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 = null;

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

        }
        if (multiThrowable != null) {
            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();
    }
    
    @Override
    protected synchronized void stopInternal() throws LifecycleException {

        // Stop our thread
        threadStop();

        setState(LifecycleState.STOPPING);

        // Stop the Valves in our pipeline (including the basic), if any
        if (pipeline instanceof Lifecycle &&
                ((Lifecycle) pipeline).getState().isAvailable()) {
            ((Lifecycle) pipeline).stop();
        }

        // Stop 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 StopChild(children[i])));
        }

        boolean fail = false;
        for (Future<Void> result : results) {
            try {
                result.get();
            } catch (Exception e) {
                log.error(sm.getString("containerBase.threadedStopFailed"), e);
                fail = true;
            }
        }
        if (fail) {
            throw new LifecycleException(
                    sm.getString("containerBase.threadedStopFailed"));
        }

        // Stop our subordinate components, if any
        Realm realm = getRealmInternal();
        if (realm instanceof Lifecycle) {
            ((Lifecycle) realm).stop();
        }
        Cluster cluster = getClusterInternal();
        if (cluster instanceof Lifecycle) {
            ((Lifecycle) cluster).stop();
        }
    }

    @Override
    protected void destroyInternal() throws LifecycleException {

        Realm realm = getRealmInternal();
        if (realm instanceof Lifecycle) {
            ((Lifecycle) realm).destroy();
        }
        Cluster cluster = getClusterInternal();
        if (cluster instanceof Lifecycle) {
            ((Lifecycle) cluster).destroy();
        }

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

        // Remove children now this container is being destroyed
        for (Container child : findChildren()) {
            removeChild(child);
        }

        // Required if the child is destroyed directly.
        if (parent != null) {
            parent.removeChild(this);
        }

        // If init fails, this may be null
        if (startStopExecutor != null) {
            startStopExecutor.shutdownNow();
        }

        super.destroyInternal();
    }
    
     @Override
    public void backgroundProcess() {

        if (!getState().isAvailable())
            return;

        Cluster cluster = getClusterInternal();
        if (cluster != null) {
            try {
                cluster.backgroundProcess();
            } catch (Exception e) {
                log.warn(sm.getString("containerBase.backgroundProcess.cluster",
                        cluster), e);
            }
        }
        Realm realm = getRealmInternal();
        if (realm != null) {
            try {
                realm.backgroundProcess();
            } catch (Exception e) {
                log.warn(sm.getString("containerBase.backgroundProcess.realm", realm), e);
            }
        }
        Valve current = pipeline.getFirst();
        while (current != null) {
            try {
                current.backgroundProcess();
            } catch (Exception e) {
                log.warn(sm.getString("containerBase.backgroundProcess.valve", current), e);
            }
            current = current.getNext();
        }
        fireLifecycleEvent(Lifecycle.PERIODIC_EVENT, null);
    }

    protected void threadStart() {

        if (thread != null)
            return;
        if (backgroundProcessorDelay <= 0)
            return;

        threadDone = false;
        String threadName = "ContainerBackgroundProcessor[" + toString() + "]";
        thread = new Thread(new ContainerBackgroundProcessor(), threadName);
        thread.setDaemon(true);
        thread.start();

    }

}

    initInternal()的作用是创建一个可执行的线程池。

    ``startInternal()`的作用是启动自身及其子组件。看如下代码：

    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])));
}

    以上代码截取自函数内部，通过findChildren()获得所有的子组件，然后在线程池中启动子组件。其中，StartChild有如下定义：

    private static class StartChild implements Callable<Void> {

    private Container child;

    public StartChild(Container child) {
        this.child = child;
    }

    @Override
    public Void call() throws LifecycleException {
        child.start();
        return null;
    }
}

    Container类直接实现接口Lifecycle，一般子组件都会直接继承于containnerBase，即一般组件都会间接继承LifecycleBase类，则调用StartChild类的call()方法，会间接的调用LifecycleBase实现的start()方法，递归的启动所有的组件。

    在startInternal()方法后，有一函数threadStart()，该函数负责启动后台线程。
    具体实现如下：

    protected void threadStart() {

    if (thread != null)
        return;
    if (backgroundProcessorDelay <= 0)
        return;
    threadDone = false;
    String threadName = "ContainerBackgroundProcessor[" + toString() + "]";
    thread = new Thread(new ContainerBackgroundProcessor(), threadName);
    thread.setDaemon(true);
    thread.start();

}

    将后台线程执行代码backgroundProcess()注册到ContainerBackgroundProcessor中，保证周期性的执行后台程序。

    note

    • ContainerBackgroundProcesor将符合要求的子组件的后台程序打包运行，即用同一个线程执行多个后台程序，可以节约资源

    tomcat 事件机制

    重新回到Lifecycle接口定义，定义剩下部分如下：

    public interface Lifecycle {


    // ----------------------------------------------------- Manifest Constants

    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";


    // --------------------------------------------------------- Public Methods

    public void addLifecycleListener(LifecycleListener listener);

    public LifecycleListener[] findLifecycleListeners();

    public void removeLifecycleListener(LifecycleListener listener);
}

    我们发现，在Lifecycle中定义了13种事件变量。前面10种变量和生命周期状态一一映射（LifecycleState枚举类型的第二个参数）。

    LifecycleListener为监听者，当有事件到来时，执行lifecycleEvent函数。形式如下：

    public interface LifecycleListener {

    public void lifecycleEvent(LifecycleEvent event);

}

    其中LifecycleEvent封装了事件名称和发出事件的组件。

    在lifecycleBase中，实现了增加监听者和移除监听者的函数，函数如下：

    public abstract class LifecycleBase implements Lifecycle {
    private final List<LifecycleListener> lifecycleListeners = new CopyOnWriteArrayList<>();
    
    @Override
    public void addLifecycleListener(LifecycleListener listener) {
        lifecycleListeners.add(listener);
    }

    @Override
    public LifecycleListener[] findLifecycleListeners() {
        return lifecycleListeners.toArray(new LifecycleListener[0]);
    }

    @Override
    public void removeLifecycleListener(LifecycleListener listener) {
        lifecycleListeners.remove(listener);
    }
    
    //执行所有的监听者函数
    protected void fireLifecycleEvent(String type, Object data) {
        LifecycleEvent event = new LifecycleEvent(this, type, data);
        for (LifecycleListener listener : lifecycleListeners) {
            listener.lifecycleEvent(event);
        }
    }
    
    //...
}

    查看LifecycleBase，我们来看具体怎么实现事件通知机制。LifecycleBase的init()函数部分如下：

    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);
}

    可以看到，函数通过setStateInternal来改变其生命周期，当生命周期改变，一定会导致事件的发生，我们看setStateInternal的源码，关键源码如下：

    private synchronized void setStateInternal(LifecycleState state,
            Object data, boolean check) throws LifecycleException {

    //...

    this.state = state;
    String lifecycleEvent = state.getLifecycleEvent();
    if (lifecycleEvent != null) {
        fireLifecycleEvent(lifecycleEvent, data);
    }
}

    可以看到，在生命周期改变的时候，自动向事件监听者发送消息，供事件监听者处理。

    note

    • 除了与事件绑定的10个事件外，还有一个周期性事件、配置启动事件与配置停止事件，使用方法类似。

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