序

本文主要研究一下dubbo的AwaitingNonWebApplicationListener

AwaitingNonWebApplicationListener

dubbo-spring-boot-project-2.7.3/dubbo-spring-boot-compatible/autoconfigure/src/main/java/org/apache/dubbo/spring/boot/context/event/AwaitingNonWebApplicationListener.java

public class AwaitingNonWebApplicationListener implements SmartApplicationListener {

    private static final String[] WEB_APPLICATION_CONTEXT_CLASSES = new String[]{
            "org.springframework.web.context.WebApplicationContext"
 
,"org.springframework.boot.web.reactive.context.ReactiveWebApplicationContext"
    };

    private static final Logger logger = LoggerFactory.getLogger(AwaitingNonWebApplicationListener.class);

    private static final Class<? extends ApplicationEvent>[] SUPPORTED_APPLICATION_EVENTS =
            of(ApplicationReadyEvent.class,ContextClosedEvent.class);

    private static final AtomicBoolean awaited = new AtomicBoolean(false
 
);

    private static final Lock lock = new ReentrantLock();

    private static final Condition condition = lock.newCondition();

    private static final ExecutorService executorService = newSingleThreadExecutor();

    private static <T> T[] of(T... values) {
        return values;
    }

    static AtomicBoolean getAwaited
 
() {
        return awaited;
    }

    @Override
    public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) {
        return containsElement(SUPPORTED_APPLICATION_EVENTS,eventType);
    }

    @Override
    public boolean supportsSourceType(Class<?> sourceType) {
        return true;
    }

    @Override
    public void onApplicationEvent(ApplicationEvent event) {
        if (event instanceof ApplicationReadyEvent) {
            onApplicationReadyEvent((ApplicationReadyEvent) event);
        } else if (event instanceof ContextClosedEvent) {
            onContextClosedEvent((ContextClosedEvent) event);
        }
    }

    @Override
    public int getOrder() {
        return LOWEST_PRECEDENCE;
    }

    protected void onApplicationReadyEvent(ApplicationReadyEvent event) {

        final ConfigurableApplicationContext applicationContext = event.getApplicationContext();

        if (!isRootApplicationContext(applicationContext) || isWebApplication(applicationContext)) {
            return;
        }

        await();
    }

    private boolean isRootApplicationContext(ApplicationContext applicationContext) {
        return applicationContext.getParent() == null;
    }

    private boolean isWebApplication(ApplicationContext applicationContext) {
        boolean webApplication = false;
        for (String contextClass : WEB_APPLICATION_CONTEXT_CLASSES) {
            if (isAssignable(contextClass,applicationContext.getClass(),applicationContext.getClassLoader())) {
                webApplication = true;
                break;
            }
        }
        return webApplication;
    }

    private static boolean isAssignable(String target,Class<?> type,ClassLoader classLoader) {
        try {
            return ClassUtils.resolveClassName(target,classLoader).isAssignableFrom(type);
        } catch (Throwable ex) {
            return false;
        }
    }

    protected void onContextClosedEvent(ContextClosedEvent event) {
        release();
        shutdown();
    }

    protected void await() {

        // has been waited,return immediately
        if (awaited.get()) {
            return;
        }

        if (!executorService.isShutdown()) {
            executorService.execute(() -> executeMutually(() -> {
                while (!awaited.get()) {
                    if (logger.isInfoEnabled()) {
                        logger.info(" [Dubbo] Current Spring Boot Application is await...");
                    }
                    try {
                        condition.await();
                    } catch (InterruptedException e) {
                        Thread.currentThread().interrupt();
                    }
                }
            }));
        }
    }

    protected void release() {
        executeMutually(() -> {
            while (awaited.compareAndSet(false,true)) {
                if (logger.isInfoEnabled()) {
                    logger.info(" [Dubbo] Current Spring Boot Application is about to shutdown...");
                }
                condition.signalAll();
            }
        });
    }

    private void shutdown() {
        if (!executorService.isShutdown()) {
            // Shutdown executorService
            executorService.shutdown();
        }
    }

    private void executeMutually(Runnable runnable) {
        try {
            lock.lock();
            runnable.run();
        } finally {
            lock.unlock();
        }
    }
}
複製程式碼

• AwaitingNonWebApplicationListener實現了SmartApplicationListener介面，其supportsEventType支援ApplicationReadyEvent.class,ContextClosedEvent.class
• onApplicationEvent判斷是ApplicationReadyEvent時執行onApplicationReadyEvent方法；判斷是ContextClosedEvent時，執行onContextClosedEvent方法
• onApplicationReadyEvent對於rootApplicationContext或者是nonWebApplicationContext執行await方法，該方法會註冊一個非同步執行緒去執行condition.await()；onContextClosedEvent則執行release及shutdown方法，release方法會更新awaited為true，然後執行condition.signalAll()，shutdown方法則關閉executorService

AwaitingNonWebApplicationListenerTest

dubbo-spring-boot-project-2.7.3/dubbo-spring-boot-compatible/autoconfigure/src/test/java/org/apache/dubbo/spring/boot/context/event/AwaitingNonWebApplicationListenerTest.java

public class AwaitingNonWebApplicationListenerTest {

    @Test
    public void init() {
        AtomicBoolean awaited = AwaitingNonWebApplicationListener.getAwaited();
        awaited.set(false);

    }

    @Test
    public void testSingleContextNonWebApplication() {
        new SpringApplicationBuilder(Object.class)
                .web(false)
                .run().close();
        AtomicBoolean awaited = AwaitingNonWebApplicationListener.getAwaited();
        Assert.assertTrue(awaited.get());
    }

    @Test
    public void testMultipleContextNonWebApplication() {
        new SpringApplicationBuilder(Object.class)
                .parent(Object.class)
                .web(false)
                .run().close();
        AtomicBoolean awaited = AwaitingNonWebApplicationListener.getAwaited();
        Assert.assertTrue(awaited.get());
    }

}
複製程式碼

• AwaitingNonWebApplicationListenerTest驗證了SingleContextNonWebApplication及MultipleContextNonWebApplication

小結

• AwaitingNonWebApplicationListener實現了SmartApplicationListener介面，其supportsEventType支援ApplicationReadyEvent.class,ContextClosedEvent.class
• onApplicationEvent判斷是ApplicationReadyEvent時執行onApplicationReadyEvent方法；判斷是ContextClosedEvent時，執行onContextClosedEvent方法
• onApplicationReadyEvent對於rootApplicationContext或者是nonWebApplicationContext執行await方法，該方法會註冊一個非同步執行緒去執行condition.await()；onContextClosedEvent則執行release及shutdown方法，release方法會更新awaited為true，然後執行condition.signalAll()，shutdown方法則關閉executorService

doc

• AwaitingNonWebApplicationListener