聊聊reactor-logback的AsyncAppender

序

本文主要研究一下reactor-logback的AsyncAppender

AsyncAppender

reactor-logback/src/main/java/reactor/logback/AsyncAppender.java

public class AsyncAppender extends ContextAwareBase
		implements Appender, AppenderAttachable,
		           CoreSubscriber {

	private final AppenderAttachableImpl    aai      =
			new AppenderAttachableImpl();
	private final FilterAttachableImpl      fai      =
			new FilterAttachableImpl();
	private final AtomicReference> delegate =
			new AtomicReference>();

	private String                            name;
	private WorkQueueProcessor processor;

	private int     backlog           = 1024 * 1024;
	private boolean includeCallerData = false;
	private boolean started           = false;

	//......
}	

AsyncAppender继承了ContextAwareBase，同时实现了Appender、AppenderAttachable、CoreSubscriber接口

CoreSubscriber

reactor/core/CoreSubscriber.java

public interface CoreSubscriber extends Subscriber {

	/**
	 * Request a {@link Context} from dependent components which can include downstream
	 * operators during subscribing or a terminal {@link org.reactivestreams.Subscriber}.
	 *
	 * @return a resolved context or {@link Context#empty()}
	 */
	default Context currentContext(){
		return Context.empty();
	}

	/**
	 * Implementors should initialize any state used by {@link #onNext(Object)} before
	 * calling {@link Subscription#request(long)}. Should further {@code onNext} related
	 * state modification occur, thread-safety will be required.
	 * 

	 *    Note that an invalid request {@code <= 0} will not produce an onError and
	 *    will simply be ignored or reported through a debug-enabled
	 *    {@link reactor.util.Logger}.
	 *
	 * {@inheritDoc}
	 */
	@Override
	void onSubscribe(Subscription s);
}

CoreSubscriber继承了Subscriber接口，Subscriber接口定义了onSubscribe(Subscription s)、onNext、onError、onComplete方法

onSubscribe

	public void onSubscribe(Subscription s) {
		try {
			doStart();
		}
		catch (Throwable t) {
			addError(t.getMessage(), t);
		}
		finally {
			started = true;
			s.request(Long.MAX_VALUE);
		}
	}

	protected void doStart() {
	}	

onSubscribe方法执行doStart，标记started为true，同时触发s.request(Long.MAX_VALUE)

onNext

	public void onNext(ILoggingEvent iLoggingEvent) {
		aai.appendLoopOnAppenders(iLoggingEvent);
	}

onNext调用AppenderAttachableImpl的appendLoopOnAppenders方法

onError

	public void onError(Throwable t) {
		addError(t.getMessage(), t);
	}

onError主要是添加错误信息到logback的status

onComplete

	public void onComplete() {
		try {
			Appender appender = delegate.getAndSet(null);
			if (appender != null){
				doStop();
				appender.stop();
				aai.detachAndStopAllAppenders();
			}
		}
		catch (Throwable t) {
			addError(t.getMessage(), t);
		}
		finally {
			started = false;
		}
	}

	protected void doStop() {
	}	

onComplete则执行doStop、appender.stop()、aai.detachAndStopAllAppenders()，最后标记started为false

Appender.doAppend

	public void doAppend(ILoggingEvent evt) throws LogbackException {
		if (getFilterChainDecision(evt) == FilterReply.DENY) {
			return;
		}
		evt.prepareForDeferredProcessing();
		if (includeCallerData) {
			evt.getCallerData();
		}
		try {
			queueLoggingEvent(evt);
		}
		catch (Throwable t) {
			addError(t.getMessage(), t);
		}
	}

	protected void queueLoggingEvent(ILoggingEvent evt) {
		if (null != delegate.get()) {
			processor.onNext(evt);
		}
	}	

doAppend方法先判断是否需要DENY，是则直接返回，之后主要执行queueLoggingEvent，它在delegate不为null时执行processor.onNext(evt)

LifeCycle.start

	public void start() {
		startDelegateAppender();

		processor = WorkQueueProcessor.builder().name("logger")
		                                                       .bufferSize(backlog)
		                                                       .autoCancel(false)
		                                                       .build();
		processor.subscribe(this);
	}

	private void startDelegateAppender() {
		Appender delegateAppender = delegate.get();
		if (null != delegateAppender && !delegateAppender.isStarted()) {
			delegateAppender.start();
		}
	}

	public void addAppender(Appender newAppender) {
		if (delegate.compareAndSet(null, newAppender)) {
			aai.addAppender(newAppender);
		}
		else {
			throw new IllegalArgumentException(delegate.get() + " already attached.");
		}
	}		

start方法执行startDelegateAppender，然后创建WorkQueueProcessor(默认bufferSize为1024 * 1024)，并subscribe当前实例；addAppender方法会设置delegate，并往AppenderAttachableImpl添加appender

stop

	public void stop() {
		processor.onComplete();
	}

stop方法执行processor.onComplete()

小结

reactor-logback基于WorkQueueProcessor提供了另外一种AsyncAppender，它不是基于BlockingQueue而是基于RingBuffer来实现的。其onSubscribe方法执行doStart，标记started为true，同时触发s.request(Long.MAX_VALUE)；onNext调用AppenderAttachableImpl的appendLoopOnAppenders方法；onComplete则执行doStop、appender.stop()、aai.detachAndStopAllAppenders()，最后标记started为false；doAppend方法先判断是否需要DENY，是则直接返回，之后主要执行queueLoggingEvent，它在delegate不为null时执行processor.onNext(evt)。