evenbus四种模式 POSTING、MAIN、BACKGROUND、ASYNC
POSTING：默认模式，在哪个线程发布消息就要在哪个线程接受消息
MAIN：指定接受者在主线程接受消息，无论是在哪个线程发布消息
BACKGROUND：指定接受者在子线程接受消息，主线程发布要在子线程接收消息，子线程发布还在他的线程接收消息
ASYNC:指定在子线程接受消息无论是什么线程发布。

evenbus只要处理接受事件的模式就可以，发布事件并不主要

源码：

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 {
                    // temporary: technically not correct as poster not decoupled from subscriber
                    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);
        }
    }

priority 属性 对于相同模式下，priority属性大的优先处理数据。