番石榴异步事件总线侦听器按顺序被触发。

Question

我正在开发一个Java应用程序，它发出应该异步处理的事件，因为事件处理依赖于IO，我希望它与核心逻辑分离。

我正在为这个用例尝试番石榴EventBus。为了启用异步事件处理，我在缓存的线程池执行器中使用AsyncEventBus。

当触发多个事件时，事件侦听器似乎按顺序执行，尽管运行在不同的线程上。

事件生成器类

public class MyEventEmitter {
    private static final Logger logger = LogManager.getLogger(MyEventEmitter.class);
    private EventBus eventBus;
    public MyEventEmitter(EventBus eventBus) {
        this.eventBus = eventBus;
    }
    public void emitEvent() {
        logger.info("[TEST] Emitting event");
        eventBus.post("String event");
        eventBus.post("String event");
        eventBus.post("String event");
        eventBus.post("String event");
    }
}

事件侦听器类

public class EventListener {

    private static final Logger logger = LogManager.getLogger(EventListener.class);
    private static int eventsHandled;
    private EventBus eventBus;
    public EventListener(EventBus eventBus) {
        this.eventBus = eventBus;
        this.eventBus.register(this);
    }

    @Subscribe
    public void stringEventDelayed(String event) throws InterruptedException{
        eventsHandled++;
        logger.info("[TEST] Async Event START " + event);
        Thread.sleep(1000);
        logger.info("[TEST] Async Event END " + event);

    }
}

EventBus设置

public class MainModule extends AbstractModule {

    @Override
    protected void configure() {
    }

    @Provides
    public EventListener getEventListener(EventBus eventBus){
        return new EventListener(eventBus);
    }

    @Singleton
    @Provides
    public EventBus getEventBus(){
        return new AsyncEventBus(Executors.newFixedThreadPool(4));
    }

    @Provides
    public MyEventEmitter getMyEventEmitter(EventBus eventBus){
        return new MyEventEmitter(eventBus);
    }
}

输出日志如下所示：

[INFO ] 2022-06-29 19:26:22.333 [main] EventListener - [TEST] EventListener setup
 [INFO ] 2022-06-29 19:26:22.345 [main] MyEventEmitter - [TEST] Emitting event
 [INFO ] 2022-06-29 19:26:22.346 [pool-2-thread-1] EventListener - [TEST] Async Event START String event
 [INFO ] 2022-06-29 19:26:23.348 [pool-2-thread-1] EventListener - [TEST] Async Event END String event
 [INFO ] 2022-06-29 19:26:23.348 [pool-2-thread-4] EventListener - [TEST] Async Event START String event
 [INFO ] 2022-06-29 19:26:24.353 [pool-2-thread-4] EventListener - [TEST] Async Event END String event
 [INFO ] 2022-06-29 19:26:24.359 [pool-2-thread-3] EventListener - [TEST] Async Event START String event
 [INFO ] 2022-06-29 19:26:25.361 [pool-2-thread-3] EventListener - [TEST] Async Event END String event
 [INFO ] 2022-06-29 19:26:25.361 [pool-2-thread-2] EventListener - [TEST] Async Event START String event
 [INFO ] 2022-06-29 19:26:26.364 [pool-2-thread-2] EventListener - [TEST] Async Event END String event

如上文所示，所有异步侦听器似乎都是一个接一个地执行，而不是并发执行。

我尝试过更改执行程序类型，尝试在本地调试，并尝试搜索，但是找不到任何特定于我的问题的内容。

Answer 1

来自EventBus Javadocs：

EventBus保证不会同时从多个线程调用订阅者方法，除非该方法通过携带AllowConcurrentEvents注释显式地允许它。如果这个注释不存在，订阅者方法不需要担心被重入，除非也是从EventBus外部调用的。

您应该用@AllowConcurrentEvents注释订阅者方法。