spring-cloud-netflix-hystrix 原理源碼分析:
本文主要針對 spring-cloud-dependencies Hoxton.SR4版本, spring-cloud-starter-netflix-hystrix 源碼的解析。
對於未接觸過 hystrix 的小夥伴可以參考 https://www.cnblogs.com/wuzhenzhao/p/9473073.html 進行一些基礎知識的瞭解。
本文主要從以下幾個點來分析:
- 手寫實現簡易版 Hystrix 體驗。
- RXJava 基礎知識體驗。
- Hystrix 源碼流程分析。
手寫實現簡易版 Hystrix 體驗:
繼上文的博客鏈接,我們知道了Hystrix 提供了多種方式讓我們實現服務降級。我們可以通過註解 @HystrixCommand、或者繼承 HystrixCommand 來實現降級,以及一些請求合併等操作。
我們需要知道的是,當我們採用 @HystrixCommand 註解來實現服務降級,在Hystrix 的內部是採用 AOP 的方式進行攔截處理請求的,我們這裏就先來實現一下簡易版的 Hystrix 來體會一下,主要分爲以下步驟
- 定義自己的@HystrixCommand 註解。
- 實現攔截請求的處理邏輯。
- 測試調用。
1.自定義註解 @WuzzHystrixCommand
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface WuzzHystrixCommand {
/**
* 默認超時時間
*
* @return
*/
int timeout() default 1000;
/**
* 回退方法
*
* @return
*/
String fallback() default "";
}
2.編寫切面類,實現簡易的邏輯處理
@Component
@Aspect
public class WuzzHystrixCommandAspect {
//線程池的處理,基於這個線程池的處理統計可以達到 THREAD 資源限流
ExecutorService executorService = Executors.newFixedThreadPool(10);
//註解切點
@Pointcut(value = "@annotation(com.wuzz.demo.custom.hystrix.WuzzHystrixCommand)")
public void pointCut() {
}
//環繞通知
@Around(value = "pointCut()&&@annotation(hystrixCommand)")
public Object doPointCut(ProceedingJoinPoint joinPoint, WuzzHystrixCommand hystrixCommand) throws InterruptedException, ExecutionException, TimeoutException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
int timeout = hystrixCommand.timeout();
//前置的判斷邏輯
Future future = executorService.submit(() -> {
try {
return joinPoint.proceed(); //執行目標方法
} catch (Throwable throwable) {
throwable.printStackTrace();
}
return null;
});
Object result;
try {// 使用 future 來實現超時
result = future.get(timeout, TimeUnit.MILLISECONDS);
} catch (InterruptedException | ExecutionException | TimeoutException e) {
e.printStackTrace();
future.cancel(true);
// ?
if (StringUtils.isBlank(hystrixCommand.fallback())) {
throw e;
}
//調用fallback
result = invokeFallback(joinPoint, hystrixCommand.fallback());
}
return result;
}
private Object invokeFallback(ProceedingJoinPoint joinPoint, String fallback) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
//獲取被代理的方法的參數和Method
MethodSignature signature = (MethodSignature) joinPoint.getSignature();
Method method = signature.getMethod();
Class<?>[] parameterTypes = method.getParameterTypes();
//得到fallback方法
try {
Method fallbackMethod = joinPoint.getTarget().getClass().getMethod(fallback, parameterTypes);
fallbackMethod.setAccessible(true);
//完成反射調用
return fallbackMethod.invoke(joinPoint.getTarget(), joinPoint.getArgs());
} catch (Exception e) {
e.printStackTrace();
throw e;
}
}
}
3. 編寫測試,調用:
@WuzzHystrixCommand(fallback = "customFallback", timeout = 3000)
@GetMapping("/custom/hystrix/test")
public String test() {
Map map = new HashMap<>();
map.put("id", 666);
return restTemplate.getForObject(REST_URL_PREFIX + "/hello?id={id}", String.class, map);
}
public String customFallback() {
return "custom 請求被降級";
}
正常得調用是沒有問題的,這個時候我們把服務提供方的服務接口裏 sleep 3秒來模仿調用超時,在訪問接口:
相信小夥伴們有了一些心得了,只不過Hystrix裏面得實現是很複雜的 ,沒有我們這麼簡單。
RXJava 基礎知識體驗:
上文的博文連接中也講到了 RXJava的簡單例子,這裏由於馬上我們要去看 Hystrix的源碼了,我們這裏寫一個類似於源碼中的例子,這樣來幫助我們更容易理解。
public class RxJavaDemo {
// ReactiveX Java 響應式編程框架(android)
// Java stream() java8
//觀察者模式
public static void main(String[] args) throws ExecutionException, InterruptedException {
final String[] datas = new String[]{"登錄"};
final Action0 onComplated = new Action0() {
@Override
public void call() {
System.out.println("on Complated");
}
};
//老師(被觀察者)
Observable<String> observable = Observable.defer(new Func0<Observable<String>>() {
@Override
public Observable<String> call() {
Observable observable1 = Observable.from(datas);
return observable1.doOnCompleted(onComplated);
}
});
//學生(觀察者)
Observer observer = new Observer() {
@Override
public void onCompleted() {
System.out.println("Observer: onCompleted");
}
@Override
public void onError(Throwable throwable) {
System.out.println("Observer: onError");
}
@Override
public void onNext(Object o) {
System.out.println("on Next:" + o);
}
};
// observable.subscribe(observer); //建立訂閱關係
String s = observable.toBlocking().toFuture().get();//建立訂閱關係
System.out.println(s);
}
}
寫這個例子的目的主要是想說明,我們可能對於 RXJava 的 API可能不是很熟悉,但是我們一定要知道對於 Observable 實例來說, call 方法纔是關鍵,而 observable.toBlocking().toFuture().get() 是用於獲取執行結果的。在 Hystrix的源碼中能看到。瞭解一下,我們直接進入Hystrix的源碼
Hystrix 源碼流程分析:
需要注意的是,Hystrix用到了RxJava這個框架,它是一個響應式編程框架,在Android裏面用得比較多,所以很多同學對它不是很瞭解。如果不瞭解的話,看Hystrix的源碼就會有點困難。
Hystrix的數據統計是採用的滑動窗口,關於滑動窗口我這裏就不深入研究了,又興趣的同學可以參考我另外一篇博客, Sentinel 限流原理 進行了解,也可以直接訪問 滑動窗口在線演示地址。
Hystrix熔斷的@HystrixCommand註解,是通過HystrixCommandAspect這個切面來處理的。其中我們關注@Around註解聲明的方法,它針對於請求合併,以及降級的註解進行代理。這裏我們重點針對HystrixCommand這個註解進行詳細分析。
@Aspect
public class HystrixCommandAspect {
private static final Map<HystrixPointcutType, MetaHolderFactory> META_HOLDER_FACTORY_MAP;
static {
META_HOLDER_FACTORY_MAP = ImmutableMap.<HystrixPointcutType, MetaHolderFactory>builder()
.put(HystrixPointcutType.COMMAND, new CommandMetaHolderFactory())
.put(HystrixPointcutType.COLLAPSER, new CollapserMetaHolderFactory())
.build();
}
// 熔斷降級切點
@Pointcut("@annotation(com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand)")
public void hystrixCommandAnnotationPointcut() {
}
// 請求合併切點
@Pointcut("@annotation(com.netflix.hystrix.contrib.javanica.annotation.HystrixCollapser)")
public void hystrixCollapserAnnotationPointcut() {
}
// 環繞通知
@Around("hystrixCommandAnnotationPointcut() || hystrixCollapserAnnotationPointcut()")
public Object methodsAnnotatedWithHystrixCommand(final ProceedingJoinPoint joinPoint) throws Throwable {
// 獲取目標方法信息
Method method = getMethodFromTarget(joinPoint);
Validate.notNull(method, "failed to get method from joinPoint: %s", joinPoint);
if (method.isAnnotationPresent(HystrixCommand.class) && method.isAnnotationPresent(HystrixCollapser.class)) {
throw new IllegalStateException("method cannot be annotated with HystrixCommand and HystrixCollapser " +
"annotations at the same time");
}
MetaHolderFactory metaHolderFactory = META_HOLDER_FACTORY_MAP.get(HystrixPointcutType.of(method));
// 獲取元數據,比如調用方法,HystrixProperty註解數據、方法參數等
MetaHolder metaHolder = metaHolderFactory.create(joinPoint);
//獲取調用者,它持有一個命令對象,並且可以在合適的時候通過這個命令對象完成具體的業務邏輯
HystrixInvokable invokable = HystrixCommandFactory.getInstance().create(metaHolder);
ExecutionType executionType = metaHolder.isCollapserAnnotationPresent() ?
metaHolder.getCollapserExecutionType() : metaHolder.getExecutionType();
Object result;
try {
//是否是響應式的(由於我們這些都是同步的會走這個邏輯)
if (!metaHolder.isObservable()) {
result = CommandExecutor.execute(invokable, executionType, metaHolder);
} else {
result = executeObservable(invokable, executionType, metaHolder);
}
} catch (HystrixBadRequestException e) {
throw e.getCause();
} catch (HystrixRuntimeException e) {
throw hystrixRuntimeExceptionToThrowable(metaHolder, e);
}
return result;
}
// ......
}
然後進入 CommandExecutor#execute 方法這個方法主要用來執行命令,從代碼中可以看出這裏有三個執行類型,分別是同步、異步、以及響應式。其中,響應式又分爲Cold Observable(observable.toObservable()) 和 HotObservable(observable.observe())默認的executionType=SYNCHRONOUS ,同步請求。
- execute():同步執行,返回一個單一的對象結果,發生錯誤時拋出異常。
- queue():異步執行,返回一個 Future 對象,包含着執行結束後返回的單一結果。
- observe():這個方法返回一個 Observable 對象,它代表操作的多個結果,但是已經被訂閱者消費掉了。
- toObservable():這個方法返回一個 Observable 對象,它代表操作的多個結果,需要咱們自己手動訂閱並消費掉。
接着調用HystrixCommand.execute()方法,這個方法中,首先調用queue(),這個方法會返回一個future對象。
public R execute() {
try {
return queue().get();
} catch (Exception e) {
throw Exceptions.sneakyThrow(decomposeException(e));
}
}
queue這個方法中,返回了一個Future對象,這個future對象的實現是f,f是以匿名內部類,它是Java.util.concurrent中定一個的一個異步帶返回值對象。當調用queue().get()方法時,最終是委派給了delegate.get 方法。
public Future<R> queue() {
/*
* The Future returned by Observable.toBlocking().toFuture() does not implement the
* interruption of the execution thread when the "mayInterrupt" flag of Future.cancel(boolean) is set to true;
* thus, to comply with the contract of Future, we must wrap around it.
*/
final Future<R> delegate = toObservable().toBlocking().toFuture();
final Future<R> f = new Future<R>() {
@Override
public boolean cancel(boolean mayInterruptIfRunning) {
// ......省略代碼
@Override
public R get() throws InterruptedException, ExecutionException {
return delegate.get();
}
@Override
public R get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
return delegate.get(timeout, unit);
}
};
// ...省略代碼
return f;
}
在上述代碼中,重點來了,構建了一個 java.util.concurrent.Future ,然後調用 get的時候委派給 delegate,而 delegate來自於 toObservable().toBlocking().toFuture(); 這正是我們上面例子裏面得代碼。所以我們現在的重點應該放在 toObservable() 方法中:
AbstractCommand.toObservable :通過Observable定義一個被觀察者,這個被觀察者會被toObservable().toBlocking().toFuture() ,實際上就是返回可獲得 run() 抽象方法執行結果的Future 。 run() 方法由子類實現,執行正常的業務邏輯。在下面這段代碼中,當存在subscriber時,便會調用Func0#call() 方法,而這個subscriber是在 toBlocking() 中被訂閱的。到這還是我們上面的例子裏面的代碼。該方法主要做了以下幾件事:
-
創建一些命令供後續的回調使用
-
調用 isRequestCachingEnabled(); 判斷請求結果緩存功能是否開啓,如果開啓並且命中了緩存,則會以Observable形式返回一個緩存結果
-
創建執行命令的Observable: hystrixObservable,
-
當緩存處於開啓狀態並且沒有命中緩存時,則創建一個“訂閱了執行命令的Observable”:HystrixCommandResponseFromCache
-
創建存儲到緩存的Observable: HystrixCachedObservable當緩存特性沒有開啓時,則返回執行命令的Observable。
-
將toCache添加到緩存中,返回獲取緩存的Observable:fromCache
-
如果添加失敗: fromCache!=null, 則調用 toCache.unsubscribe() 方法,取消HystrixCachedObservable 的訂閱
-
如果添加成功,則調用 toCache.toObservable(); 獲得緩存Observable
-
-
當緩存特性沒有開啓時,則返回執行命令的Observable。
public Observable<R> toObservable() {
final AbstractCommand<R> _cmd = this;
//會在Observable結束前觸發回調該call方法,無論是正常還是異常終止
//doOnCompleted handler already did all of the SUCCESS work
//doOnError handler already did all of the FAILURE/TIMEOUT/REJECTION/BAD_REQUEST work
final Action0 terminateCommandCleanup = new Action0() {
@Override
public void call() {
if (_cmd.commandState.compareAndSet(CommandState.OBSERVABLE_CHAIN_CREATED, CommandState.TERMINAL)) {
handleCommandEnd(false); //user code never ran
} else if (_cmd.commandState.compareAndSet(CommandState.USER_CODE_EXECUTED, CommandState.TERMINAL)) {
handleCommandEnd(true); //user code did run
}
}
};
//取消訂閱時的監聽會進行回調該 call方法
//mark the command as CANCELLED and store the latency (in addition to standard cleanup)
final Action0 unsubscribeCommandCleanup = new Action0() {
@Override
public void call() {
if (_cmd.commandState.compareAndSet(CommandState.OBSERVABLE_CHAIN_CREATED, CommandState.UNSUBSCRIBED)) {
if (!_cmd.executionResult.containsTerminalEvent()) {
_cmd.eventNotifier.markEvent(HystrixEventType.CANCELLED, _cmd.commandKey);
try {
executionHook.onUnsubscribe(_cmd);
} catch (Throwable hookEx) {
logger.warn("Error calling HystrixCommandExecutionHook.onUnsubscribe", hookEx);
}
_cmd.executionResultAtTimeOfCancellation = _cmd.executionResult
.addEvent((int) (System.currentTimeMillis() - _cmd.commandStartTimestamp), HystrixEventType.CANCELLED);
}
handleCommandEnd(false); //user code never ran
} else if (_cmd.commandState.compareAndSet(CommandState.USER_CODE_EXECUTED, CommandState.UNSUBSCRIBED)) {
if (!_cmd.executionResult.containsTerminalEvent()) {
_cmd.eventNotifier.markEvent(HystrixEventType.CANCELLED, _cmd.commandKey);
try {
executionHook.onUnsubscribe(_cmd);
} catch (Throwable hookEx) {
logger.warn("Error calling HystrixCommandExecutionHook.onUnsubscribe", hookEx);
}
_cmd.executionResultAtTimeOfCancellation = _cmd.executionResult
.addEvent((int) (System.currentTimeMillis() - _cmd.commandStartTimestamp), HystrixEventType.CANCELLED);
}
handleCommandEnd(true); //user code did run
}
}
};
final Func0<Observable<R>> applyHystrixSemantics = new Func0<Observable<R>>() {
@Override
public Observable<R> call() {
if (commandState.get().equals(CommandState.UNSUBSCRIBED)) {
return Observable.never(); // 立即終止整個流程。
}//返回執行命令的Observable
return applyHystrixSemantics(_cmd);
}
};
final Func1<R, R> wrapWithAllOnNextHooks = new Func1<R, R>() {
@Override
public R call(R r) {
R afterFirstApplication = r;
try {
afterFirstApplication = executionHook.onComplete(_cmd, r);
} catch (Throwable hookEx) {
logger.warn("Error calling HystrixCommandExecutionHook.onComplete", hookEx);
}
try {
return executionHook.onEmit(_cmd, afterFirstApplication);
} catch (Throwable hookEx) {
logger.warn("Error calling HystrixCommandExecutionHook.onEmit", hookEx);
return afterFirstApplication;
}
}
};
final Action0 fireOnCompletedHook = new Action0() {
@Override
public void call() {
try {
executionHook.onSuccess(_cmd);
} catch (Throwable hookEx) {
logger.warn("Error calling HystrixCommandExecutionHook.onSuccess", hookEx);
}
}
};
return Observable.defer(new Func0<Observable<R>>() {
@Override
public Observable<R> call() {
/* this is a stateful object so can only be used once */
// CAS保證命令只執行一次
if (!commandState.compareAndSet(CommandState.NOT_STARTED, CommandState.OBSERVABLE_CHAIN_CREATED)) {
IllegalStateException ex = new IllegalStateException("This instance can only be executed once. Please instantiate a new instance.");
//TODO make a new error type for this
throw new HystrixRuntimeException(FailureType.BAD_REQUEST_EXCEPTION, _cmd.getClass(), getLogMessagePrefix() + " command executed multiple times - this is not permitted.", ex, null);
}
// 命令開始時間戳
commandStartTimestamp = System.currentTimeMillis();
// 打印日誌
if (properties.requestLogEnabled().get()) {
// log this command execution regardless of what happened
if (currentRequestLog != null) {
currentRequestLog.addExecutedCommand(_cmd);
}
}
// 緩存開關,緩存KEY(這個是Hystrix中請求緩存功能,hystrix支持將一個請求結果緩存起來,
// 下一個具有相同key的請求將直接從緩存中取出結果,減少請求開銷)
final boolean requestCacheEnabled = isRequestCachingEnabled();
final String cacheKey = getCacheKey();
/* try from cache first */
if (requestCacheEnabled) {//如果開啓了緩存機制,則從緩存中獲取結果
HystrixCommandResponseFromCache<R> fromCache = (HystrixCommandResponseFromCache<R>) requestCache.get(cacheKey);
if (fromCache != null) {
isResponseFromCache = true;
return handleRequestCacheHitAndEmitValues(fromCache, _cmd);
}
}
// 聲明執行命令的Observable
Observable<R> hystrixObservable =
Observable.defer(applyHystrixSemantics)
.map(wrapWithAllOnNextHooks);
Observable<R> afterCache;
// put in cache 保存請求結果到緩存中
if (requestCacheEnabled && cacheKey != null) {
// wrap it for caching
HystrixCachedObservable<R> toCache = HystrixCachedObservable.from(hystrixObservable, _cmd);
HystrixCommandResponseFromCache<R> fromCache = (HystrixCommandResponseFromCache<R>) requestCache.putIfAbsent(cacheKey, toCache);
if (fromCache != null) {
// another thread beat us so we'll use the cached value instead
toCache.unsubscribe();
isResponseFromCache = true;
return handleRequestCacheHitAndEmitValues(fromCache, _cmd);
} else {
// we just created an ObservableCommand so we cast and return it
afterCache = toCache.toObservable();
}
} else {
afterCache = hystrixObservable;
}
return afterCache
//會在Observable結束前觸發回調,無論是正常還是異常終止
.doOnTerminate(terminateCommandCleanup) // perform cleanup once (either on normal terminal state (this line), or unsubscribe (next line))
//取消訂閱時的監聽
.doOnUnsubscribe(unsubscribeCommandCleanup) // perform cleanup once
//Observable正常終止時的監聽
.doOnCompleted(fireOnCompletedHook);
}
});
}
所以在 AbstractCommand#toObservable 方法裏,我們只需要看這個返回的 Observable 對象的 call 方法即可,而在這裏 默認沒有開啓緩存的話就是 :
Observable<R> hystrixObservable =
Observable.defer(applyHystrixSemantics)
.map(wrapWithAllOnNextHooks);
那麼我們主要來看 applyHystrixSemantics ,在該方法上面定義了
final Func0<Observable<R>> applyHystrixSemantics = new Func0<Observable<R>>() {
@Override
public Observable<R> call() {
if (commandState.get().equals(CommandState.UNSUBSCRIBED)) {
return Observable.never();
}
return applyHystrixSemantics(_cmd);
}
};
假設緩存特性未開啓或者未命中緩存,那麼代碼將執行 applyHystrixSemantics 。傳入的_cmd是一個GenericCommand(可以斷點看看),最終執行這個command中的run方法,本質就是完成對queryOrder方法的代理。
circuitBreaker.allowRequest() 如果爲true,表示當前不處於熔斷狀態,正常執行,否則,調用 handleShortCircuitViaFallback 實現服務降級,如果我們配置了fallback方法,則會獲得我們配置的fallback執行。執行路徑爲 : handleShortCircuitViaFallback ->getFallbackOrThrowException ->getFallbackObservable->HystrixCommand.getFallbackObservable->GenericCommand.getFallback();
如果當前hystrix處於未熔斷狀態,則
- getExecutionSemaphore 判斷當前策略是否爲信號量(TryableSemaphoreNoOp/TryableSemaphoreActual),如果是,則調用 tryAcquire 來獲取信號量。如果當前信號量滿了,則調用 handleSemaphoreRejectionViaFallback 方法。
- 調用 executeCommandAndObserve 獲取命令執行Observable。
private Observable<R> applyHystrixSemantics(final AbstractCommand<R> _cmd) {
// mark that we're starting execution on the ExecutionHook
// if this hook throws an exception, then a fast-fail occurs with no fallback. No state is left inconsistent
executionHook.onStart(_cmd);
/* determine if we're allowed to execute */
// 判斷是否處於熔斷狀態
if (circuitBreaker.allowRequest()) {
final TryableSemaphore executionSemaphore = getExecutionSemaphore();
final AtomicBoolean semaphoreHasBeenReleased = new AtomicBoolean(false);
final Action0 singleSemaphoreRelease = new Action0() {//操作命令
@Override
public void call() {
if (semaphoreHasBeenReleased.compareAndSet(false, true)) {
executionSemaphore.release();
}
}
};
final Action1<Throwable> markExceptionThrown = new Action1<Throwable>() {
@Override
public void call(Throwable t) {
eventNotifier.markEvent(HystrixEventType.EXCEPTION_THROWN, commandKey);
}
};
// 是否開啓信號量資源隔離,未配置走 com.netflix.hystrix.AbstractCommand.TryableSemaphoreNoOp#tryAcquire 默認返回通過
if (executionSemaphore.tryAcquire()) {
try {
/* used to track userThreadExecutionTime */
executionResult = executionResult.setInvocationStartTime(System.currentTimeMillis());
return executeCommandAndObserve(_cmd) // 執行命令,以下三個是回調,可以不看
.doOnError(markExceptionThrown)
.doOnTerminate(singleSemaphoreRelease)
.doOnUnsubscribe(singleSemaphoreRelease);
} catch (RuntimeException e) {
return Observable.error(e);
}
} else {
// 走服務降級方法
return handleSemaphoreRejectionViaFallback();
}
} else {
return handleShortCircuitViaFallback();
}
}
我們縣來看一下執行失敗進入降級的邏輯,這裏我們直接進入到 HystrixCommand#getFallbackObservable
@Override
final protected Observable<R> getFallbackObservable() {
return Observable.defer(new Func0<Observable<R>>() {
@Override
public Observable<R> call() {
try {
return Observable.just(getFallback());
} catch (Throwable ex) {
return Observable.error(ex);
}
}
});
}
這裏的 getFallback 我們應該熟悉了,因爲通過集成 HystrixCommand 類來實現熔斷降級的時候我們重寫了這個方法,而通過註解的話是通過 GenericCommand進行代理實現得,我們Debug一下,看看該類的 getFallback 方法做了什麼:
可以發現他拿到了我們配置在註解上的方法,這一點是不是跟上文的手寫是一個道理呢? 然後進行調用獲取結果返回。
好了,回到 AbstractCommand#applyHystrixSemantics ,接下去我們按照正常邏輯走到 AbstractCommand#executeCommandAndObserve,主要做了以下三件事情
- 定義不同的回調,doOnNext、doOnCompleted、onErrorResumeNext、doOnEach。
- 調用executeCommandWithSpecifiedIsolation獲得執行命令的Observable
- 若執行命令超時特性開啓,調用 Observable.lift 方法實現執行命令超時功能。
private Observable<R> executeCommandAndObserve(final AbstractCommand<R> _cmd) {
final HystrixRequestContext currentRequestContext = HystrixRequestContext.getContextForCurrentThread();
// Action和Func都是定義的一個動作,Action是無返回值,Func是有返回值
// doOnNext中的回調。即命令執行之前執行的操作
final Action1<R> markEmits = new Action1<R>() {
@Override
public 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.markCommandExecution(getCommandKey(), properties.executionIsolationStrategy().get(), (int) latency, executionResult.getOrderedList());
eventNotifier.markEvent(HystrixEventType.SUCCESS, commandKey);
executionResult = executionResult.addEvent((int) latency, HystrixEventType.SUCCESS);
circuitBreaker.markSuccess();
}
}
};
// doOnCompleted中的回調。命令執行完畢後執行的操作
final Action0 markOnCompleted = new Action0() {
@Override
public void call() {
if (!commandIsScalar()) {
long latency = System.currentTimeMillis() - executionResult.getStartTimestamp();
eventNotifier.markCommandExecution(getCommandKey(), properties.executionIsolationStrategy().get(), (int) latency, executionResult.getOrderedList());
eventNotifier.markEvent(HystrixEventType.SUCCESS, commandKey);
executionResult = executionResult.addEvent((int) latency, HystrixEventType.SUCCESS);
circuitBreaker.markSuccess();
}
}
};
// onErrorResumeNext中的回調。命令執行失敗後的回退邏輯
final Func1<Throwable, Observable<R>> handleFallback = new Func1<Throwable, Observable<R>>() {
@Override
public Observable<R> call(Throwable t) {
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);
}
}
};
// doOnEach中的回調。`Observable`每發射一個數據都會執行這個回調,設置請求上下文
final Action1<Notification<? super R>> setRequestContext = new Action1<Notification<? super R>>() {
@Override
public void call(Notification<? super R> rNotification) {
setRequestContextIfNeeded(currentRequestContext);
}
};
Observable<R> execution;
// 是否開啓超時降級
if (properties.executionTimeoutEnabled().get()) {
execution = executeCommandWithSpecifiedIsolation(_cmd)
.lift(new HystrixObservableTimeoutOperator<R>(_cmd));
} else {
execution = executeCommandWithSpecifiedIsolation(_cmd);
}
// 發射
return execution.doOnNext(markEmits)
.doOnCompleted(markOnCompleted)
.onErrorResumeNext(handleFallback)
.doOnEach(setRequestContext);
}
executeCommandWithSpecifiedIsolation:這個方法首先是根據當前不同的資源隔離策略執行不同的邏輯,THREAD、SEMAPHORE:
private Observable<R> executeCommandWithSpecifiedIsolation(final AbstractCommand<R> _cmd) {
// 是否開啓 THREAD 資源隔離降級
if (properties.executionIsolationStrategy().get() == ExecutionIsolationStrategy.THREAD) {
// ......省略代碼
} else { // 否則進入這裏
return Observable.defer(new Func0<Observable<R>>() {
@Override
public Observable<R> call() {
executionResult = executionResult.setExecutionOccurred();
if (!commandState.compareAndSet(CommandState.OBSERVABLE_CHAIN_CREATED, CommandState.USER_CODE_EXECUTED)) {
return Observable.error(new IllegalStateException("execution attempted while in state : " + commandState.get().name()));
}
metrics.markCommandStart(commandKey, threadPoolKey, ExecutionIsolationStrategy.SEMAPHORE);
// semaphore isolated
// store the command that is being run
endCurrentThreadExecutingCommand = Hystrix.startCurrentThreadExecutingCommand(getCommandKey());
try {
executionHook.onRunStart(_cmd);
executionHook.onExecutionStart(_cmd);
// 真正的執行
return getUserExecutionObservable(_cmd); //the getUserExecutionObservable method already wraps sync exceptions, so this shouldn't throw
} catch (Throwable ex) {
//If the above hooks throw, then use that as the result of the run method
return Observable.error(ex);
}
}
});
}
}
這裏就不展開實現細節,我們直接看執行的方法 getUserExecutionObservable 。然後會執行 HystrixCommand#getExecutionObservable
@Override
final protected Observable<R> getExecutionObservable() {
return Observable.defer(new Func0<Observable<R>>() {
@Override
public Observable<R> call() {
try {
return Observable.just(run());
} catch (Throwable ex) {
return Observable.error(ex);
}
}
}).doOnSubscribe(new Action0() {
@Override
public void call() {
// Save thread on which we get subscribed so that we can interrupt it later if needed
executionThread.set(Thread.currentThread());
}
});
}
又看到熟悉的代碼 ,這個 run() 方法在通過集成 HystrixCommand 類來實現熔斷降級的時候我們重寫了這個方法,是真正的執行方法。
這裏最終調用的是run方法,通過Observable.just, just是RxJava中的一個操作符,它可以接受一個或者多個參數來創建一個Observable對象。而這個run()方法是一個抽象方法,在HystrixCommand中並沒有實現,而是在子類中實現,而此時傳遞的cmd=GenricCommand正好實現了HystrixCommand,重寫了run方法。
@Override
protected Object run() throws Exception {
LOGGER.debug("execute command: {}", getCommandKey().name());
return process(new Action() {
@Override
Object execute() {
return getCommandAction().execute(getExecutionType());
}
});
}
大家有沒有發現,這裏的實現和我們前面自定義的 HystrixCommandService 實現是一樣的,同樣是集成HystrixCommand,重寫run方法。這裏也是如此。
- 首先調用 getCommandAction() 方法獲取 CommandAction ,我們的示例中獲取到的是MethodExecutionAction 。
- 然後調用 MethodExecutionAction.execute 方法,傳入 ExecutionType 參數,我們的示例中傳入的是 ExecutionType.SYNCHRONOUS 。
拿到我們的真實方法進行調用返回。下面附上整個過程的流程圖: