EventBus使用及源码浅析

看源码其实就和小时候拆玩具差不多，拆其实挺简单的，难的是拆了还能组合回来…
----沃兹基硕德

基本使用

使用的是EventBus-3.1.1

1.创建事件类，这里创建了LogEvent类，事件类理论上可以是任意对象，当然尽量命名规范予以区别

public class LogEvent {}

2.在某个类中注册事件，需要创建一个以事件为参数的方法，并且加以@Subscribe注解，@Subscribe有三个可选参数：

Subscribe参数	说明
threadMode	接收事件动作所在的线程，默认为ThreadMode.POSTING
sticky	是否粘性。指是否具有事件发布再注册也能接收事件的特殊功能，默认为false
priority	优先级。数值越大，在相同的线程下越先接收到事件，默认为0

threadMode类型	说明
ThreadMode.POSTING	与发布事件动作(post)所在的线程相同
ThreadMode.MAIN	主线程，在Android中指UI线程
ThreadMode.MAIN_ORDERED	主线程，总是可以顺序接收
ThreadMode.BACKGROUND	后台线程，如果发布事件在主线程，则自建线程，反之与发布线程相同
ThreadMode.ASYNC	异步线程，总是自建线程接收事件

public class MainActivity extends FragmentActivity{

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		//注册
        EventBus.getDefault().register(this);
	}

	//注册是必须的
	@Subscribe(threadMode = ThreadMode.POSTING, sticky = false, priority = 0)
	public void onMain(LogEvent event){
		//填充逻辑
	}

	@Override
	protected void onDestroy() {
		//反注册
        EventBus.getDefault().unregister(this);
		super.onDestroy();
	}
}

3.在某个类中调用post ：

    EventBus.getDefault().post(new LogEvent());
    EventBus.getDefault().postSticky(new LogEvent());//sticky=true使用

完毕。
就是这么简单易用。

源码分析

按照调用习惯，先看一下getDefault()里面有什么吧：

//EventBus.java
	private static final EventBusBuilder DEFAULT_BUILDER = new EventBusBuilder();
	
	static volatile EventBus defaultInstance;

    public static EventBus getDefault() {
        if (defaultInstance == null) {
            synchronized (EventBus.class) {
                if (defaultInstance == null) {
                    defaultInstance = new EventBus();
                }
            }
        }
        return defaultInstance;
    }
	
    public EventBus() {
        this(DEFAULT_BUILDER);
    }

嗯，果然没什么好看的。就是个DCL的单例模式。
很久以前，我以为有getDefault()就会其他getSpecial()之类的，事实证明想多了…

需要注意一下的就是这里的volatile关键字，这是DCL单例中必备的一个关键字，复习一下：
1.保证了被修饰的变量对所有线程的可见性；
2.不能保证原子性，因与其修饰变量相关的写入操作无法保证原子性
推荐看看Java并发编程：volatile关键字解析

另外，注意一下这个EventBusBuilder，这里结合两个类看一下一些比较重要的属性：

//EventBus.java
    EventBus(EventBusBuilder builder) {
    	//以Event为key的map
        subscriptionsByEventType = new HashMap<>();
        //以Subscriber为key的map
        typesBySubscriber = new HashMap<>();
        //粘性事件map
        stickyEvents = new ConcurrentHashMap<>();
        //判断是否为主线程的依据
        mainThreadSupport = builder.getMainThreadSupport();
        //用于寻找@Subscribe的方法
        subscriberMethodFinder = new SubscriberMethodFinder(builder.subscriberInfoIndexes,
                builder.strictMethodVerification, builder.ignoreGeneratedIndex);
        //是否考虑event的继承关系
        eventInheritance = builder.eventInheritance;

		//略过部分属性
    }

//EventBusBuilder.java
public class EventBusBuilder {
    private final static ExecutorService DEFAULT_EXECUTOR_SERVICE = Executors.newCachedThreadPool();
	//默认处理event的继承关系
    boolean eventInheritance = true;
    //默认为false
    boolean ignoreGeneratedIndex;
    //默认为无界线程池
    ExecutorService executorService = DEFAULT_EXECUTOR_SERVICE;
	//主线程相关类
    MainThreadSupport mainThreadSupport;
	//略过部分属性
    EventBusBuilder() {
    }
}

这些属性大概有个印象就行，中途会用到的还会回来看的，接下来看下register干了什么。

注册

//EventBus.java
    public void register(Object subscriber) {
        Class<?> subscriberClass = subscriber.getClass();
        //找到当前订阅类注解Subscribe的方法
        List<SubscriberMethod> subscriberMethods = subscriberMethodFinder.findSubscriberMethods(subscriberClass);
        synchronized (this) {
            for (SubscriberMethod subscriberMethod : subscriberMethods) {
            	//遍历去建立当前订阅类与标记方法的映射关系
                subscribe(subscriber, subscriberMethod);
            }
        }
    }

这里看到就两个步骤，第一步是找到订阅类中所有注解过的方法，第二步是建立这些方法与订阅类的映射关系。

第一步.找到订阅类中所有注解过的方法

就之前的Demo来说，这里的subscriber就是MainActivity，看看里面subscriberMethodFinder.findSubscriberMethods做了什么事情吧：

//SubscriberMethodFinder.java

	private static final Map<Class<?>, List<SubscriberMethod>> METHOD_CACHE = new ConcurrentHashMap<>();
	
	//找到与订阅类相关的方法，并封装为SubscriberMethod   
    List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) {
        List<SubscriberMethod> subscriberMethods = METHOD_CACHE.get(subscriberClass);
        if (subscriberMethods != null) {
            return subscriberMethods;
        }
		//默认为false
        if (ignoreGeneratedIndex) {
            subscriberMethods = findUsingReflection(subscriberClass);
        } else {
            subscriberMethods = findUsingInfo(subscriberClass);
        }
        //为空代表着些订阅类并没有注解Subscribe的方法，抛出异常
        if (subscriberMethods.isEmpty()) {
            throw new EventBusException("Subscriber " + subscriberClass
                    + " and its super classes have no public methods with the @Subscribe annotation");
        } else {
            METHOD_CACHE.put(subscriberClass, subscriberMethods);
            return subscriberMethods;
        }
    }

默认情况下进了findUsingInfo方法：

//SubscriberMethodFinder.java
    private static final int POOL_SIZE = 4;
    private static final FindState[] FIND_STATE_POOL = new FindState[POOL_SIZE];

    private List<SubscriberMethod> findUsingInfo(Class<?> subscriberClass) {
        FindState findState = prepareFindState();
        findState.initForSubscriber(subscriberClass);
        while (findState.clazz != null) {
            findState.subscriberInfo = getSubscriberInfo(findState);
            //首次为空
            if (findState.subscriberInfo != null) {
            	//不为空就拿已经缓存的
                SubscriberMethod[] array = findState.subscriberInfo.getSubscriberMethods();
                for (SubscriberMethod subscriberMethod : array) {
                    if (findState.checkAdd(subscriberMethod.method, subscriberMethod.eventType)) {
                        findState.subscriberMethods.add(subscriberMethod);
                    }
                }
            } else {
            	//重点，首次注册订阅是进了此方法，使用反射机制
                findUsingReflectionInSingleClass(findState);
            }
            findState.moveToSuperclass();
        }
        //拿到List<SubscriberMethod>释放findState
        return getMethodsAndRelease(findState);
    }
    
    private FindState prepareFindState() {
        synchronized (FIND_STATE_POOL) {
            for (int i = 0; i < POOL_SIZE; i++) {
                FindState state = FIND_STATE_POOL[i];
                if (state != null) {
                    FIND_STATE_POOL[i] = null;
                    return state;
                }
            }
        }
        return new FindState();
    }
    
    static class FindState {
        final List<SubscriberMethod> subscriberMethods = new ArrayList<>();
        final Map<Class, Object> anyMethodByEventType = new HashMap<>();
        final Map<String, Class> subscriberClassByMethodKey = new HashMap<>();
        final StringBuilder methodKeyBuilder = new StringBuilder(128);

        Class<?> subscriberClass;
        Class<?> clazz;
        boolean skipSuperClasses;
        SubscriberInfo subscriberInfo;

        void initForSubscriber(Class<?> subscriberClass) {
            this.subscriberClass = clazz = subscriberClass;
            skipSuperClasses = false;
            subscriberInfo = null;
        }

		//略过部分代码
    }

这里的FindState不必太过在意，暂且当作一个类似缓存的东西存在好了，这里创建了一个长度为4的FindState数组作为缓存区，重点还是看findUsingReflectionInSingleClass做了什么：

//SubscriberMethodFinder.java
    private void findUsingReflectionInSingleClass(FindState findState) {
        Method[] methods;
        try {
            //尝试找到订阅类所有方法
            methods = findState.clazz.getDeclaredMethods();
        } catch (Throwable th) {
            //尝试找到订阅类所有public方法
            methods = findState.clazz.getMethods();
            findState.skipSuperClasses = true;
        }
        //遍历方法，开始筛选目标
        for (Method method : methods) {
            int modifiers = method.getModifiers();
            //只在Public方法中寻找，且不带abstract、static修饰
            if ((modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0) {
                Class<?>[] parameterTypes = method.getParameterTypes();
                //只在仅有1个参数的方法中寻找目标
                if (parameterTypes.length == 1) {
                    Subscribe subscribeAnnotation = method.getAnnotation(Subscribe.class);
                    //只在有Subscribe注解的方法中寻找目标
                    if (subscribeAnnotation != null) {
                    	//拿到Event事件类型
                        Class<?> eventType = parameterTypes[0]; 
                        //首次订阅为true                       
                        if (findState.checkAdd(method, eventType)) {
                            ThreadMode threadMode = subscribeAnnotation.threadMode();
                            //拿到threadMode、stciky、priority等参数，封装SubscriberMethod
                            findState.subscriberMethods.add(new SubscriberMethod(method, eventType, threadMode, subscribeAnnotation.priority(), subscribeAnnotation.sticky()));
                        }
                    }
                } else if (strictMethodVerification && method.isAnnotationPresent(Subscribe.class)) {
                	//方法参数数量不是1个，抛出异常
                    String methodName = method.getDeclaringClass().getName() + "." + method.getName();
                    throw new EventBusException("@Subscribe method " + methodName +
                            "must have exactly 1 parameter but has " + parameterTypes.length);
                }
            } else if (strictMethodVerification && method.isAnnotationPresent(Subscribe.class)) {
            	//方法修饰符不为单纯的public，抛出异常
                String methodName = method.getDeclaringClass().getName() + "." + method.getName();
                throw new EventBusException(methodName +
                        " is a illegal @Subscribe method: must be public, non-static, and non-abstract");
            }
        }
    }

这个方法就是通过反射在寻找合法的订阅接收事件的方法，这里的反射有两个地方需要注意一下，一是getDeclaredMethods和getMethods的区别，复习一下：

方法	说明
getDeclaredMethods	返回某个类的所有方法，包括公共、保护、默认（包）访问和私有方法，但不包括继承的方法。包括它所实现接口的方法。
getMethods	返回某个类的所有公用（public）方法包括其继承类的公用方法，包括它所实现接口的方法。

二是类似(modifiers & Modifier.PUBLIC) != 0 && (modifiers & MODIFIERS_IGNORE) == 0的判断，可以通过得到方法的修饰符整数标记getModifiers和PUBLIC等整数常量进行位与(&)运算的结果是否非0的方式来判断方法的修饰符：

//SubscriberMethodFinder.java
    private static final int MODIFIERS_IGNORE = Modifier.ABSTRACT | Modifier.STATIC | BRIDGE | SYNTHETIC;
//Modifier.java
    public static final int PUBLIC = 0x00000001;
    
    public static boolean isPublic(int mod) {
        return (mod & PUBLIC) != 0;
    }

话说回来，我们通过findUsingInfo拿到了SubscriberMethods，那么findUsingReflection呢？

//SubscriberMethodFinder.java
        if (ignoreGeneratedIndex) {
            subscriberMethods = findUsingReflection(subscriberClass);
        } else {
            subscriberMethods = findUsingInfo(subscriberClass);
        }

其实也是一样的：

//SubscriberMethodFinder.java
    private List<SubscriberMethod> findUsingReflection(Class<?> subscriberClass) {
        FindState findState = prepareFindState();
        findState.initForSubscriber(subscriberClass);
        while (findState.clazz != null) {
        	//通过同样的方法拿到
            findUsingReflectionInSingleClass(findState);
            findState.moveToSuperclass();
        }
        return getMethodsAndRelease(findState);
    }

最终通过getMethodsAndRelease方法将findState释放回收掉，返回了subscriberMethods。

//SubscriberMethodFinder.java
    private List<SubscriberMethod> getMethodsAndRelease(FindState findState) {
        List<SubscriberMethod> subscriberMethods = new ArrayList<>(findState.subscriberMethods);
        findState.recycle();
        synchronized (FIND_STATE_POOL) {
            for (int i = 0; i < POOL_SIZE; i++) {
                if (FIND_STATE_POOL[i] == null) {
                    FIND_STATE_POOL[i] = findState;
                    break;
                }
            }
        }
        return subscriberMethods;
    }

就之前的demo来说，SubscriberMethods列表中应该只有一个元素，这个值封装的属性参照一下类：

public class SubscriberMethod {
    final Method method;
    final ThreadMode threadMode;
    final Class<?> eventType;
    final int priority;
    final boolean sticky;
    String methodString;

    public SubscriberMethod(Method method, Class<?> eventType, ThreadMode threadMode, int priority, boolean sticky) {
        this.method = method;
        this.threadMode = threadMode;
        this.eventType = eventType;
        this.priority = priority;
        this.sticky = sticky;
    }
}

那么demo中封装有SubscriberMethod各参数应该为：

类型	参数	值
Method	method	onMain
Class<?>	eventType	LogEvent
ThreadMode	threadMode	ThreadMode.POSTING
int	priority	0
boolean	sticky	false

现在注册的第一个步骤算是完成了，接下来就是建立映射关系了。

第二步.建立订阅方法与订阅类的映射关系

遍历所有的SubscriberMethod，与当前订阅类建立联系：

//EventBus.java
	//以Event类型为键,以与Event相关的映射关系Subscription为值
    private final Map<Class<?>, CopyOnWriteArrayList<Subscription>> subscriptionsByEventType;
    //以订阅类为键，以订阅类可接收的Event列表为值
    private final Map<Object, List<Class<?>>> typesBySubscriber;
    
    private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
        Class<?> eventType = subscriberMethod.eventType;
        //封装了Subscription
        Subscription newSubscription = new Subscription(subscriber, subscriberMethod);
        CopyOnWriteArrayList<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
        //首次订阅第一个Event为空
        if (subscriptions == null) {
            subscriptions = new CopyOnWriteArrayList<>();
            subscriptionsByEventType.put(eventType, subscriptions);
        } else {
            if (subscriptions.contains(newSubscription)) {
                throw new EventBusException("Subscriber " + subscriber.getClass() + " already registered to event " + eventType);
            }
        }

		//此处是实现priority的关键，总体就是间接为subscriptions通过priority排了序
        int size = subscriptions.size();
        for (int i = 0; i <= size; i++) {
        	//只有priority比当前subscriberMethod方法更大时，才能插队，否则依次插入列表尾部
            if (i == size || subscriberMethod.priority > subscriptions.get(i).subscriberMethod.priority) {
                subscriptions.add(i, newSubscription);
                break;
            }
        }

		//添加订阅类与event的映射关系
        List<Class<?>> subscribedEvents = typesBySubscriber.get(subscriber);
        if (subscribedEvents == null) {
            subscribedEvents = new ArrayList<>();
            typesBySubscriber.put(subscriber, subscribedEvents);
        }
        subscribedEvents.add(eventType);

		//处理sticky=true的情况，如果sticky=false，注册到这里就算完毕了
        if (subscriberMethod.sticky) {
        	//默认为true，默认处理event继承关系
            if (eventInheritance) {                
                Set<Map.Entry<Class<?>, Object>> entries = stickyEvents.entrySet();
                for (Map.Entry<Class<?>, Object> entry : entries) {
                    Class<?> candidateEventType = entry.getKey();
                    //判断前者是否为后者的上层类（父类或接口）或相同类
                    if (eventType.isAssignableFrom(candidateEventType)) {
                        Object stickyEvent = entry.getValue();
                        //去发粘性事件
                        checkPostStickyEventToSubscription(newSubscription, stickyEvent);
                    }
                }
            } else {
                Object stickyEvent = stickyEvents.get(eventType);
                //去发粘性事件
                checkPostStickyEventToSubscription(newSubscription, stickyEvent);
            }
        }
    }

可以看到subscribe中已经完成了与priority、sticky相关逻辑，
对priority，是采用了间接对subscriptions排序，在这里完全可以推测出后面的post逻辑应该在遍历subscriptions列表调用了通过反射得出的订阅方法，这里的顺序就体现出了priority的作用；
对sticky，是当前就调用了checkPostStickyEventToSubscription方法，这里也可以推测这个方法应该实现了对订阅方法的调用；

就demo来说，

newSubscription = Subscription(MainActvity,subscriberMethod(onMain,LogEvent,ThreadMode.POSTING,0,false)

typesBySubscriber = Map(MainActivity,List[LogEvent.class])

subscriptionsByEventType = Map(LogEvent.class,CopyOnWriteArrayList[newSubscription])

stickyEvents = Map()//如果有，则为Map(LogEvent.class,

来看看checkPostStickyEventToSubscription做了什么吧：

//EventBus.java
    private void checkPostStickyEventToSubscription(Subscription newSubscription, Object stickyEvent) {
        if (stickyEvent != null) {
            postToSubscription(newSubscription, stickyEvent, isMainThread());
        }
    }

调用了postToSubscription，这里已经接近终点了：

//EventBus.java
    private void postToSubscription(Subscription subscription, Object event, boolean isMainThread) {
        switch (subscription.subscriberMethod.threadMode) {
            case POSTING:
                invokeSubscriber(subscription, event);
                break;
            case MAIN:
                if (isMainThread) {
                    invokeSubscriber(subscription, event);
                } else {
                    mainThreadPoster.enqueue(subscription, event);
                }
                break;
            case MAIN_ORDERED:
                if (mainThreadPoster != null) {
                    mainThreadPoster.enqueue(subscription, event);
                } else {
                    invokeSubscriber(subscription, event);
                }
                break;
            case BACKGROUND:
                if (isMainThread) {
                    backgroundPoster.enqueue(subscription, event);
                } else {
                    invokeSubscriber(subscription, event);
                }
                break;
            case ASYNC:
                asyncPoster.enqueue(subscription, event);
                break;
            default:
                throw new IllegalStateException("Unknown thread mode: " + subscription.subscriberMethod.threadMode);
        }
    }

这里可以看到，postToSubscription用各种poster实现了对线程的切换。

看到了invoke，就知道这里应该就是调用订阅方法的地方了：

//EventBus.java
    void invokeSubscriber(Subscription subscription, Object event) {
        try {
            subscription.subscriberMethod.method.invoke(subscription.subscriber, event);
        } catch (InvocationTargetException e) {
            handleSubscriberException(subscription, event, e.getCause());
        } catch (IllegalAccessException e) {
            throw new IllegalStateException("Unexpected exception", e);
        }
    }

……
……

索然无味。

就是一个反射引用invoke，可以想见，正常的post流程最终也会走到这里。

这里的sticky之所以可以先postSticky再register也可以，是因为就代码本身来说，流程依然是在register时才真正post了，因此实现了”粘性“，使得register和postSticky可以颠倒顺序。

至此，register的逻辑就完毕了，现在来看一下post吧，来看看是否与猜想中一样呢。

发布

//EventBus.java
    public void post(Object event) {
        PostingThreadState postingState = currentPostingThreadState.get();
        List<Object> eventQueue = postingState.eventQueue;
        eventQueue.add(event);

        if (!postingState.isPosting) {
        	//判断是否为主线程
            postingState.isMainThread = isMainThread();
            postingState.isPosting = true;
            if (postingState.canceled) {
                throw new EventBusException("Internal error. Abort state was not reset");
            }
            try {
            	//发事件了
                while (!eventQueue.isEmpty()) {
                    postSingleEvent(eventQueue.remove(0), postingState);
                }
            } finally {
                postingState.isPosting = false;
                postingState.isMainThread = false;
            }
        }
    }

此处PostingThreadState和之前的FindState类似，看作一种过渡缓存就行了。

这里有一个比较有意思的地方，isMainThread，因为大家知道EventBus并不是只能用在Android中，这个判断是很有必要的，那么里面写了什么？

//EventBus.java
    private boolean isMainThread() {
        return mainThreadSupport != null ? mainThreadSupport.isMainThread() : true;
    }

//MainThreadSupport.java
public interface MainThreadSupport {

    boolean isMainThread();

    Poster createPoster(EventBus eventBus);
	
    class AndroidHandlerMainThreadSupport implements MainThreadSupport {

        private final Looper looper;

        public AndroidHandlerMainThreadSupport(Looper looper) {
            this.looper = looper;
        }

        @Override
        public boolean isMainThread() {
            return looper == Looper.myLooper();
        }

        @Override
        public Poster createPoster(EventBus eventBus) {
            return new HandlerPoster(eventBus, looper, 10);
        }
    }

}

这里自己实现了一个类AndroidHandlerMainThreadSupport，判断的方法是looper == Looper.myLooper()，即判断当前的looper是否与当前myLooper返回的Looper相同。

可以相见，AndroidHandlerMainThreadSupport的构造参数，肯定传进了Looper.getMainLooper()，这个得从很久以前的EventBusBuilder说起了，当时不是传进了一个getMainThreadSupport么？

    MainThreadSupport getMainThreadSupport() {
        if (mainThreadSupport != null) {
            return mainThreadSupport;            
        } else if (Logger.AndroidLogger.isAndroidLogAvailable()) {
            Object looperOrNull = getAndroidMainLooperOrNull();
            return looperOrNull == null ? null :
                    new MainThreadSupport.AndroidHandlerMainThreadSupport((Looper) looperOrNull);
        } else {
            return null;
        }
    }

这里！
在判断是AndroidLog是否可用？wtf？

//Logger.java
public interface Logger {

    void log(Level level, String msg);

    void log(Level level, String msg, Throwable th);

    public static class AndroidLogger implements Logger {
        static final boolean ANDROID_LOG_AVAILABLE;

        static {
            boolean android = false;
            try {
            	//6666666
                android = Class.forName("android.util.Log") != null;
            } catch (ClassNotFoundException e) {
                // OK
            }
            ANDROID_LOG_AVAILABLE = android;
        }

        public static boolean isAndroidLogAvailable() {
            return ANDROID_LOG_AVAILABLE;
        }
    }
}

没有错。
这里居然在判断当前系统是不是Android？并且使用的是寻找"android.util.Log"类，找得到？好，这就是安卓了！

如果以后google突发其想把这个类给删除了，会不会让EventBus怨念深重…

当前是Android系统就好办啦，反手就是一个getMainLooper：

//EventBusBuilder.java
    Object getAndroidMainLooperOrNull() {
        try {
            return Looper.getMainLooper();
        } catch (RuntimeException e) {
            return null;
        }
    }

回到正题，post中加入了是否为主线程的判断，然后执行了postSingleEvent：

//EventBus.java
    private void postSingleEvent(Object event, PostingThreadState postingState) throws Error {
        Class<?> eventClass = event.getClass();
        boolean subscriptionFound = false;
        if (eventInheritance) {
        	//找到所有与Event相关的父类、接口等
            List<Class<?>> eventTypes = lookupAllEventTypes(eventClass);
            int countTypes = eventTypes.size();
            for (int h = 0; h < countTypes; h++) {
                Class<?> clazz = eventTypes.get(h);
                //都发出克，一直发到不能发为止
                subscriptionFound |= postSingleEventForEventType(event, postingState, clazz);
            }
        } else {
            //发出克
            subscriptionFound = postSingleEventForEventType(event, postingState, eventClass);
        }
        if (!subscriptionFound) {
            if (logNoSubscriberMessages) {
                logger.log(Level.FINE, "No subscribers registered for event " + eventClass);
            }
            if (sendNoSubscriberEvent && eventClass != NoSubscriberEvent.class &&
                    eventClass != SubscriberExceptionEvent.class) {
                post(new NoSubscriberEvent(this, event));
            }
        }
    }

注意一下，这里的lookupAllEventTypes会找到其父类，直到找到Object为止，包括Object.class。
结合demo，此时

eventTypes = List[LogEvent.class,Object.class]

subscriptionsByEventType = Map(LogEvent.class,CopyOnWriteArrayList[newSubscription])

来吧，都通过postSingleEventForEventType发出去吧：

//EventBus.java
    private boolean postSingleEventForEventType(Object event, PostingThreadState postingState, Class<?> eventClass) {
        CopyOnWriteArrayList<Subscription> subscriptions;
        synchronized (this) {
            subscriptions = subscriptionsByEventType.get(eventClass);
        }
        if (subscriptions != null && !subscriptions.isEmpty()) {
            for (Subscription subscription : subscriptions) {
                postingState.event = event;
                postingState.subscription = subscription;
                boolean aborted = false;
                try {
                	//果然来了
                    postToSubscription(subscription, event, postingState.isMainThread);
                    aborted = postingState.canceled;
                } finally {
                    postingState.event = null;
                    postingState.subscription = null;
                    postingState.canceled = false;
                }
                if (aborted) {
                    break;
                }
            }
            return true;
        }
        return false;
    }

这里的subscriptionsByEventType.get(Object.class)在一般情况下肯定是没有值的，所以可以当作一个终止标记，这也是使用subscriptionFound |= postSingleEventForEventType(…)的原因所在，两者配合就达到了遍历所有上层类，直到没有映射关系的时候终止发送，一般情况下到超类Object.class就为止了。

最终和之前的sticky事件一样，来到了postToSubscription，然后调用invokeSubscriber。

没有任何悬念。

那么粘性事件专用的postSticky呢？

    public void postSticky(Object event) {
        synchronized (stickyEvents) {
            stickyEvents.put(event.getClass(), event);
        }
        post(event);
    }

同样走的post流程，只是在走之前将事件存入了stickyEvents中，这里就可以与之前register中的subscribe对应起来，只有调用postSticky时，stickyEvents才会有值。

    private void subscribe(Object subscriber, SubscriberMethod subscriberMethod) {
        //略过部分代码

        if (subscriberMethod.sticky) {
            if (eventInheritance) {
                Set<Map.Entry<Class<?>, Object>> entries = stickyEvents.entrySet();
                for (Map.Entry<Class<?>, Object> entry : entries) {
                    Class<?> candidateEventType = entry.getKey();
                    if (eventType.isAssignableFrom(candidateEventType)) {
                        Object stickyEvent = entry.getValue();
                        checkPostStickyEventToSubscription(newSubscription, stickyEvent);
                    }
                }
            } else {
                Object stickyEvent = stickyEvents.get(eventType);
                checkPostStickyEventToSubscription(newSubscription, stickyEvent);
            }
        }
    }

对应demo，此时

stickyEvents = Map(LogEvent.class,List[LogEvent])

至于postToSubscription中的各种Poster，都是与queue、线程池相关的东西，有兴趣可以探究一下。
比如在threadMode==ThreadMode.ASYNC时，

//EventBus.java
    private final AsyncPoster asyncPoster;

    EventBus(EventBusBuilder builder) {    
        //略过部分代码    
        asyncPoster = new AsyncPoster(this);
        //略过部分代码
    }

    private void postToSubscription(Subscription subscription, Object event, boolean isMainThread) {
        switch (subscription.subscriberMethod.threadMode) {
            //略过部分代码
            case ASYNC:
                asyncPoster.enqueue(subscription, event);
                break;
        }
    }

asyncPoster本身就集成了序列与线程的作用，

class AsyncPoster implements Runnable, Poster {

    private final PendingPostQueue queue;
    private final EventBus eventBus;

    AsyncPoster(EventBus eventBus) {
        this.eventBus = eventBus;
        queue = new PendingPostQueue();
    }

    public void enqueue(Subscription subscription, Object event) {
        PendingPost pendingPost = PendingPost.obtainPendingPost(subscription, event);
        queue.enqueue(pendingPost);
        eventBus.getExecutorService().execute(this);
    }

    @Override
    public void run() {
        PendingPost pendingPost = queue.poll();
        if(pendingPost == null) {
            throw new IllegalStateException("No pending post available");
        }
        //照样调用
        eventBus.invokeSubscriber(pendingPost);
    }
}

其他非主线程的调用都大同小异，问题不大。

反注册

这个步骤自然是清除各种缓存，重置标记。

//EventBus.java
	//以Event类型为键,以与Event相关的映射关系Subscription为值
    private final Map<Class<?>, CopyOnWriteArrayList<Subscription>> subscriptionsByEventType;
    //以订阅类为键，以订阅类可接收的Event列表为值
    private final Map<Object, List<Class<?>>> typesBySubscriber;

    public synchronized void unregister(Object subscriber) {
        List<Class<?>> subscribedTypes = typesBySubscriber.get(subscriber);
        if (subscribedTypes != null) {
            for (Class<?> eventType : subscribedTypes) {
                unsubscribeByEventType(subscriber, eventType);
            }
            typesBySubscriber.remove(subscriber);
        } else {
            logger.log(Level.WARNING, "Subscriber to unregister was not registered before: " + subscriber.getClass());
        }
    }

    private void unsubscribeByEventType(Object subscriber, Class<?> eventType) {
        List<Subscription> subscriptions = subscriptionsByEventType.get(eventType);
        if (subscriptions != null) {
            int size = subscriptions.size();
            for (int i = 0; i < size; i++) {
                Subscription subscription = subscriptions.get(i);
                if (subscription.subscriber == subscriber) {
                    subscription.active = false;
                    subscriptions.remove(i);
                    i--;
                    size--;
                }
            }
        }
    }

整个流程就这样了。

以上。