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本文主要研究一下HystrixEventNotifier

HystrixEventNotifier

/*** Abstract EventNotifier that allows receiving notifications for different events with default implementations.* <p>* See {@link HystrixPlugins} or the Hystrix GitHub Wiki for information on configuring plugins: <a* href="https://github.com/Netflix/Hystrix/wiki/Plugins">https://github.com/Netflix/Hystrix/wiki/Plugins</a>.* <p>* <b>Note on thread-safety and performance</b>* <p>* A single implementation of this class will be used globally so methods on this class will be invoked concurrently from multiple threads so all functionality must be thread-safe.* <p>* Methods are also invoked synchronously and will add to execution time of the commands so all behavior should be fast. If anything time-consuming is to be done it should be spawned asynchronously* onto separate worker threads.*/ public abstract class HystrixEventNotifier {/*** Called for every event fired.* <p>* <b>Default Implementation: </b> Does nothing* * @param eventType event type* @param key event key*/public void markEvent(HystrixEventType eventType, HystrixCommandKey key) {// do nothing}/*** Called after a command is executed using thread isolation.* <p>* Will not get called if a command is rejected, short-circuited etc.* <p>* <b>Default Implementation: </b> Does nothing* * @param key* {@link HystrixCommandKey} of command instance.* @param isolationStrategy* {@link ExecutionIsolationStrategy} the isolation strategy used by the command when executed* @param duration* time in milliseconds of executing <code>run()</code> method* @param eventsDuringExecution* {@code List<HystrixEventType>} of events occurred during execution.*/public void markCommandExecution(HystrixCommandKey key, ExecutionIsolationStrategy isolationStrategy, int duration, List<HystrixEventType> eventsDuringExecution) {// do nothing}} 復制代碼

• 這個notifier是同步調用的，因此里頭方法的實現不能太耗時，不然則會阻塞，如果方法太耗時則需要考慮異步到其他線程
• markEvent，在每個事件觸發的時候調用，markCommandExecution是在使用線程隔離方式的時候會調用

HystrixEventNotifierDefault

hystrix-core-1.5.12-sources.jar!/com/netflix/hystrix/strategy/eventnotifier/HystrixEventNotifierDefault.java

/*** Default implementations of {@link HystrixEventNotifier} that does nothing.* * @ExcludeFromJavadoc*/ public class HystrixEventNotifierDefault extends HystrixEventNotifier {private static HystrixEventNotifierDefault INSTANCE = new HystrixEventNotifierDefault();private HystrixEventNotifierDefault() {}public static HystrixEventNotifier getInstance() {return INSTANCE;} } 復制代碼

默認實現不做任何操作

HystrixEventType

hystrix-core-1.5.12-sources.jar!/com/netflix/hystrix/HystrixEventType.java

/*** Various states/events that execution can result in or have tracked.* <p>* These are most often accessed via {@link HystrixRequestLog} or {@link HystrixCommand#getExecutionEvents()}.*/ public enum HystrixEventType {EMIT(false),SUCCESS(true),FAILURE(false),TIMEOUT(false),BAD_REQUEST(true),SHORT_CIRCUITED(false),THREAD_POOL_REJECTED(false),SEMAPHORE_REJECTED(false),FALLBACK_EMIT(false),FALLBACK_SUCCESS(true),FALLBACK_FAILURE(true),FALLBACK_REJECTION(true),FALLBACK_MISSING(true),EXCEPTION_THROWN(false),RESPONSE_FROM_CACHE(true),CANCELLED(true),COLLAPSED(false),COMMAND_MAX_ACTIVE(false);private final boolean isTerminal;HystrixEventType(boolean isTerminal) {this.isTerminal = isTerminal;}public boolean isTerminal() {return isTerminal;}//....../*** List of events that throw an Exception to the caller*/public final static List<HystrixEventType> EXCEPTION_PRODUCING_EVENT_TYPES = new ArrayList<HystrixEventType>();/*** List of events that are terminal*/public final static List<HystrixEventType> TERMINAL_EVENT_TYPES = new ArrayList<HystrixEventType>();static {EXCEPTION_PRODUCING_EVENT_TYPES.add(BAD_REQUEST);EXCEPTION_PRODUCING_EVENT_TYPES.add(FALLBACK_FAILURE);EXCEPTION_PRODUCING_EVENT_TYPES.add(FALLBACK_MISSING);EXCEPTION_PRODUCING_EVENT_TYPES.add(FALLBACK_REJECTION);for (HystrixEventType eventType: HystrixEventType.values()) {if (eventType.isTerminal()) {TERMINAL_EVENT_TYPES.add(eventType);}}}//...... } 復制代碼

• 這里定了HystrixEvent的枚舉，然后還對這些事件進行了分類，分為EXCEPTION_PRODUCING_EVENT_TYPES以及EXCEPTION_PRODUCING_EVENT_TYPES兩類
• EXCEPTION_PRODUCING_EVENT_TYPES包括BAD_REQUEST、FALLBACK_FAILURE、FALLBACK_MISSING、FALLBACK_REJECTION
• TERMINAL_EVENT_TYPES主要是根據event枚舉的isTerminal屬性來，包括SUCCESS、BAD_REQUEST、FALLBACK_SUCCESS、FALLBACK_FAILURE、FALLBACK_REJECTION、FALLBACK_MISSING、RESPONSE_FROM_CACHE、CANCELLED

markCommandExecution

hystrix-core-1.5.12-sources.jar!/com/netflix/hystrix/AbstractCommand.java

/*** This decorates "Hystrix" functionality around the run() Observable.** @return R*/private Observable<R> executeCommandAndObserve(final AbstractCommand<R> _cmd) {final HystrixRequestContext currentRequestContext = HystrixRequestContext.getContextForCurrentThread();final Action1<R> markEmits = new Action1<R>() {@Overridepublic void call(R r) {if (shouldOutputOnNextEvents()) {executionResult = executionResult.addEvent(HystrixEventType.EMIT);eventNotifier.markEvent(HystrixEventType.EMIT, commandKey);}if (commandIsScalar()) {long latency = System.currentTimeMillis() - executionResult.getStartTimestamp();eventNotifier.markEvent(HystrixEventType.SUCCESS, commandKey);executionResult = executionResult.addEvent((int) latency, HystrixEventType.SUCCESS);eventNotifier.markCommandExecution(getCommandKey(), properties.executionIsolationStrategy().get(), (int) latency, executionResult.getOrderedList());circuitBreaker.markSuccess();}}};final Action0 markOnCompleted = new Action0() {@Overridepublic void call() {if (!commandIsScalar()) {long latency = System.currentTimeMillis() - executionResult.getStartTimestamp();eventNotifier.markEvent(HystrixEventType.SUCCESS, commandKey);executionResult = executionResult.addEvent((int) latency, HystrixEventType.SUCCESS);eventNotifier.markCommandExecution(getCommandKey(), properties.executionIsolationStrategy().get(), (int) latency, executionResult.getOrderedList());circuitBreaker.markSuccess();}}};final Func1<Throwable, Observable<R>> handleFallback = new Func1<Throwable, Observable<R>>() {@Overridepublic Observable<R> call(Throwable t) {circuitBreaker.markNonSuccess();Exception e = getExceptionFromThrowable(t);executionResult = executionResult.setExecutionException(e);if (e instanceof RejectedExecutionException) {return handleThreadPoolRejectionViaFallback(e);} else if (t instanceof HystrixTimeoutException) {return handleTimeoutViaFallback();} else if (t instanceof HystrixBadRequestException) {return handleBadRequestByEmittingError(e);} else {/** Treat HystrixBadRequestException from ExecutionHook like a plain HystrixBadRequestException.*/if (e instanceof HystrixBadRequestException) {eventNotifier.markEvent(HystrixEventType.BAD_REQUEST, commandKey);return Observable.error(e);}return handleFailureViaFallback(e);}}};final Action1<Notification<? super R>> setRequestContext = new Action1<Notification<? super R>>() {@Overridepublic void call(Notification<? super R> rNotification) {setRequestContextIfNeeded(currentRequestContext);}};Observable<R> execution;if (properties.executionTimeoutEnabled().get()) {execution = executeCommandWithSpecifiedIsolation(_cmd).lift(new HystrixObservableTimeoutOperator<R>(_cmd));} else {execution = executeCommandWithSpecifiedIsolation(_cmd);}return execution.doOnNext(markEmits).doOnCompleted(markOnCompleted).onErrorResumeNext(handleFallback).doOnEach(setRequestContext);} 復制代碼

• 這里在markEmits的action里頭如果是scalar command，會調用markCommandExecution
• 這里在markOnCompleted的action里頭，如果不是scalar command，則會調用markCommandExecution

小結

在HystrixCommand以及HystrixObservableCommand調用的時候，都會調用HystrixEventNotifier來發布事件，提供給開發者自定義實現，來做指標收集及監控報警。

doc

• Event Notifier

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