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熔断器有限状态器,熔断器核心接口CircuitBreaker的实现类。
先看一段CircuitBreaker 默认接口实现代码
static <T> Supplier<T> decorateSupplier(CircuitBreaker circuitBreaker, Supplier<T> supplier){
return () -> {
//判断是否允许请求通过,不通过,抛出CircuitBreakerOpenException
CircuitBreakerUtils.isCallPermitted(circuitBreaker);
long start = System.nanoTime();
try {
//反射执行业务代码,并返回结果
T returnValue = supplier.get();
long durationInNanos = System.nanoTime() - start;
//请求处理成功,触发熔断器成功处理策略
circuitBreaker.onSuccess(durationInNanos);
return returnValue;
} catch (Exception exception) {
// Do not handle java.lang.Error
long durationInNanos = System.nanoTime() - start;
//请求出现异常,触发熔断器error处理策略
circuitBreaker.onError(durationInNanos, exception);
throw exception;
}
};
}
CircuitBreaker装饰请求默认实现大同小异,熔断大体处理流程见下图:
有限状态机主要是在CLOSED、OPEN、HALF_OPEN三者之间转换,另外还有两种特殊状态: DISABLED、FORCED_OPEN。
- CLOSED → OPEN
熔断器默认初始为CLOSED状态,当请求失败率达到failureRateThreshold阀值后,熔断器处于OPEN状态,不允许所有请求通过。
- OPEN → HALF_OPEN
熔断器在处于OPEN状态后,等待waitDurationInOpenState时长后,熔断器转换到HALF_OPEN状态,允许部分请求通过。
- HALF_OPEN →OPEN
熔断器处于HALF_OPEN状态时,当请求次数达到ringBufferSizeInHalfOpenState后,判断请求失败率是否依旧超过failureRateThreshold阀值,若超过,熔断器则回到OPEN状态。
- HALF_OPEN →CLOSED
熔断器处于HALF_OPEN状态时,当请求次数达到ringBufferSizeInHalfOpenState后,判断请求失败率是否依旧超过failureRateThreshold阀值,若小于阀值,熔断器转换到CLOSED状态。
状态转换接口源码
//熔断器切换到不可用状态
public void transitionToDisabledState() {
stateTransition(DISABLED, currentState -> new DisabledState(this));
}
//熔断器切换到强制开启状态
public void transitionToForcedOpenState() {
stateTransition(FORCED_OPEN, currentState -> new ForcedOpenState(this));
}
//熔断器切换到关闭状态
public void transitionToClosedState() {
stateTransition(CLOSED, currentState -> new ClosedState(this, currentState.getMetrics()));
}
//熔断器切换到开启状态
public void transitionToOpenState() {
stateTransition(OPEN, currentState -> new OpenState(this, currentState.getMetrics()));
}
//熔断器切换到半开状态
public void transitionToHalfOpenState() {
stateTransition(HALF_OPEN, currentState -> new HalfOpenState(this));
}
//熔断器熔断状态转换
private void stateTransition(State newState, Function<CircuitBreakerState, CircuitBreakerState> newStateGenerator) {
CircuitBreakerState previousState = stateReference.getAndUpdate(currentState -> {
//若当前状态与更新状态一样,则返回
if (currentState.getState() == newState) {
return currentState;
}
//若当前状态与更新状态不一样,切换到新状态
return newStateGenerator.apply(currentState);
});
//状态发生了变化,则发布状态转换事件。evenType为:Type.STATE_TRANSITION
if (previousState.getState() != newState) {
publishStateTransitionEvent(StateTransition.transitionBetween(previousState.getState(), newState));
}
}
从源码可以看出状态转换通过AtomicReference来保证原子操作,从而实现thread-safe。
有限状态机是通过 AtomicReference<CircuitBreakerState> stateReference 保证状态转换实现线程安全。
public boolean isCallPermitted() {
//判断是否允许请求通过
boolean callPermitted = stateReference.get().isCallPermitted();
if (!callPermitted) {
//不允许,发布请求不允许被调用事件
publishCallNotPermittedEvent();
}
return callPermitted;
}
public void onSuccess(long durationInNanos) {
//发布成功事件
publishSuccessEvent(durationInNanos);
//更新熔断指标
stateReference.get().onSuccess();
}
public void onError(long durationInNanos, Throwable throwable) {
// Handle the case if the completable future throw CompletionException wrapping the original exception
// where original exception is the the one to retry not the CompletionException.
Predicate<Throwable> recordFailurePredicate = circuitBreakerConfig.getRecordFailurePredicate();
if (throwable instanceof CompletionException) {
//如果是异步异常,获取原始异常
Throwable cause = throwable.getCause();
handleThrowable(durationInNanos, recordFailurePredicate, cause);
}else{
handleThrowable(durationInNanos, recordFailurePredicate, throwable);
}
}
private void handleThrowable(long durationInNanos, Predicate<Throwable> recordFailurePredicate, Throwable throwable) {
//根据配置check是忽略该次请求的异常,还是计入失败并增加失败率
if (recordFailurePredicate.test(throwable)) {
LOG.debug("CircuitBreaker '{}' recorded a failure:", name, throwable);
publishCircuitErrorEvent(name, durationInNanos, throwable);
stateReference.get().onError(throwable);
} else {
publishCircuitIgnoredErrorEvent(name, durationInNanos, throwable);
}
}
从源码可知,熔断器是根据业务代码通俗的说是根据业务method是否抛出异常来决定处理逻辑,同时根据异常及熔断配置,来判定是否做熔断处理,还是忽略本次异常请求。
若异常为配置中可忽略异常,则本次请求不做任何失败处理,也不更新熔断指标,只发布CircuitBreakerOnIgnoredErrorEvent。
CircuitBreakerState会在后续章节讲解
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原文链接 : https://blog.csdn.net/a355586533/article/details/89207034
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