南京市高淳县建设厅网站,个人做的网站,手机网站营销,图片海报制作软件[每日一句] 也许你度过了很糟糕的一天#xff0c;但这并不代表你会因此度过糟糕的一生。 [背景介绍]
分布式系统的规模和复杂度不断增加#xff0c;随着而来的是对分布式系统可用性的要求越来越高。在各种高可用设计模式中#xff0c;【熔断、隔离、降级、限流】是经常被使…[每日一句] 也许你度过了很糟糕的一天但这并不代表你会因此度过糟糕的一生。 [背景介绍]
分布式系统的规模和复杂度不断增加随着而来的是对分布式系统可用性的要求越来越高。在各种高可用设计模式中【熔断、隔离、降级、限流】是经常被使用的。而相关的技术Hystrix本身早已算不上什么新技术但它却是最经典的技术体系。Hystrix以实现熔断降级的设计从而提高了系统的可用性。Hystrix是一个在调用端上实现断路器模式以及隔舱模式通过避免级联故障提高系统容错能力从而实现高可用设计的一个Java服务组件库。*Hystrix实现了资源隔离机制
前提介绍 Hystrix的超时检测本质上通过启动单独线程去检测的线程的执行的时间刚好就是任务超时的时间本质上就是这么个简单的逻辑。 Hystrix超时后会抛出一个 HystrixTimeoutException的异常。 超时检测逻辑
Hystrix的超时包括注册过程和执行过程两个注册过程如下
执行lift(new HystrixObservableTimeoutOperator(_cmd))关联超时检测任务。在HystrixObservableTimeoutOperator类中new TimerListener()负责创建检测任务HystrixTimer.getInstance().addTimerListener(listener)负责关联定时任务。 在HystrixObservableTimeoutOperator类中addTimerListener通过java的定时任务服务scheduleAtFixedRate在延迟超时时间后执行。
Hystrix的超时执行过程如下
在超时后执行listener.tick()方法后执行类TimerListener的tick方法在TimerListener类的tick方法中执行timeoutRunnable.run()后执行HystrixContextRunnable的run方法在HystrixContextRunnable类run方法中执行child.onError(new HystrixTimeoutException())实现超时。executeCommandWithSpecifiedIsolation(_cmd).lift(new HystrixObservableTimeoutOperator(_cmd));
private static class HystrixObservableTimeoutOperator implements Operator {final AbstractCommand originalCommand;public HystrixObservableTimeoutOperator(final AbstractCommand originalCommand) {this.originalCommand originalCommand;}public Subscribersuper R call(final Subscribersuper R child) {final CompositeSubscription s new CompositeSubscription();child.add(s);final HystrixRequestContext hystrixRequestContext HystrixRequestContext.getContextForCurrentThread();TimerListener listener new TimerListener() {public void tick() {if(originalCommand.isCommandTimedOut.compareAndSet(TimedOutStatus.NOT_EXECUTED, TimedOutStatus.TIMED_OUT)) {originalCommand.eventNotifier.markEvent(HystrixEventType.TIMEOUT,originalCommand.commandKey);s.unsubscribe();final HystrixContextRunnable timeoutRunnable new HystrixContextRunnable(originalCommand.concurrencyStrategy, hystrixRequestContext, new Runnable() {public void run() {child.onError(new HystrixTimeoutException());}});timeoutRunnable.run();}}public int getIntervalTimeInMilliseconds() {return originalCommand.properties.executionTimeoutInMilliseconds().get();}};final Reference tl HystrixTimer.getInstance().addTimerListener(listener);originalCommand.timeoutTimer.set(tl);Subscriber parent new Subscriber() {public void onCompleted() {if (isNotTimedOut()) {tl.clear();child.onCompleted();}}public void onError(Throwable e) {if (isNotTimedOut()) {tl.clear();child.onError(e);}}public void onNext(R v) {if (isNotTimedOut()) {child.onNext(v);}}private boolean isNotTimedOut() {return originalCommand.isCommandTimedOut.get() TimedOutStatus.COMPLETED ||originalCommand.isCommandTimedOut.compareAndSet(TimedOutStatus.NOT_EXECUTED,TimedOutStatus.COMPLETED);}};s.add(parent);return parent;}}public Reference addTimerListener(final TimerListener listener) {startThreadIfNeeded();Runnable r new Runnable() {public void run() {try {listener.tick();} catch (Exception e) {logger.error(Failed while ticking TimerListener, e);}}};ScheduledFuture f executor.get().getThreadPool().scheduleAtFixedRate(r,listener.getIntervalTimeInMilliseconds(), listener.getIntervalTimeInMilliseconds(),TimeUnit.MILLISECONDS);return new TimerReference(listener, f);}public class HystrixContextRunnable implements Runnable {private final Callable actual;private final HystrixRequestContext parentThreadState;public HystrixContextRunnable(Runnable actual) {this(HystrixPlugins.getInstance().getConcurrencyStrategy(), actual);}public HystrixContextRunnable(HystrixConcurrencyStrategy concurrencyStrategy, final Runnableactual) {this(concurrencyStrategy, HystrixRequestContext.getContextForCurrentThread(), actual);}public HystrixContextRunnable(final HystrixConcurrencyStrategy concurrencyStrategy,final HystrixRequestContext hystrixRequestContext, final Runnable actual) {this.actual concurrencyStrategy.wrapCallable(new Callable() {public Void call() throws Exception {actual.run();return null;}});this.parentThreadState hystrixRequestContext;}public void run() {HystrixRequestContext existingState HystrixRequestContext.getContextForCurrentThread();try {HystrixRequestContext.setContextOnCurrentThread(parentThreadState);try {actual.call();} catch (Exception e) {throw new RuntimeException(e);}} finally {HystrixRequestContext.setContextOnCurrentThread(existingState);}}
}
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