【Java】hystrix - hystrix怎么知道他已经熔断了

• Z时代
• 2024-01-10
• 分类：技术分享

public boolean allowRequest() {
// 配置了强制熔断，直接返回false
if (properties.circuitBreakerForceOpen().get()) {
// properties have asked us to force the circuit open so we will allow NO requests
return false;
}
// 强制关闭
if (properties.circuitBreakerForceClosed().get()) {
// we still want to allow isOpen() to perform it's calculations so we simulate normal behavior
isOpen();
// properties have asked us to ignore errors so we will ignore the results of isOpen and just allow all traffic through
return true;
}
return !isOpen() || allowSingleTest();
}
public boolean isOpen() {
// 获取熔断器的状态，true就是开
if (circuitOpen.get()) {
// 如果是开的，还是返回ture，留给半开的时候用
return true;
}
// 如果是关的，获取HealthCounts信息
HealthCounts health = metrics.getHealthCounts();
// 当前的请求数如果小于设置的阈值，就直接返回false，说明没开
// 比如我们设置了20，此时才19，也是没有开的
// 这个值是样品数量的值，只有足够数量的样品，才比较准确
if (health.getTotalRequests() < properties.circuitBreakerRequestVolumeThreshold().get()) {
// we are not past the minimum volume threshold for the statisticalWindow so we'll return false immediately and not calculate anything
return false;
}
// 错误比例小于设定的值，比如错误的比例超过50%，就开启熔断
if (health.getErrorPercentage() < properties.circuitBreakerErrorThresholdPercentage().get()) {
return false;
} else {
// 这边设置时间，用于半开状态
if (circuitOpen.compareAndSet(false, true)) {
// if the previousValue was false then we want to set the currentTime
circuitOpenedOrLastTestedTime.set(System.currentTimeMillis());
return true;
} else {
// How could previousValue be true? If another thread was going through this code at the same time a race-condition could have
// caused another thread to set it to true already even though we were in the process of doing the same
// In this case, we know the circuit is open, so let the other thread set the currentTime and report back that the circuit is open
return true;
}
}
}

public boolean allowSingleTest() {
long timeCircuitOpenedOrWasLastTested = circuitOpenedOrLastTestedTime.get();
// 熔断器开的时候，并且当前时间>熔断时间+休眠时间
// 也就是说休眠时间设置为5，那5秒后给他一个机会看看能不能访问，也就是半开状态
// 然后重新设置circuitOpenedOrLastTestedTime
if (circuitOpen.get() && System.currentTimeMillis() > timeCircuitOpenedOrWasLastTested + properties.circuitBreakerSleepWindowInMilliseconds().get()) {
if (circuitOpenedOrLastTestedTime.compareAndSet(timeCircuitOpenedOrWasLastTested, System.currentTimeMillis())) {
return true;
}
}
return false;
}

private static HystrixCircuitBreaker initCircuitBreaker(boolean enabled, HystrixCircuitBreaker fromConstructor,
HystrixCommandGroupKey groupKey, HystrixCommandKey commandKey,
HystrixCommandProperties properties, HystrixCommandMetrics metrics) {
if (enabled) {
if (fromConstructor == null) {
// get the default implementation of HystrixCircuitBreaker
return HystrixCircuitBreaker.Factory.getInstance(commandKey, groupKey, properties, metrics);
} else {
return fromConstructor;
}
} else {
return new NoOpCircuitBreaker();
}
}

public static HystrixCircuitBreaker getInstance(HystrixCommandKey key, HystrixCommandGroupKey group, HystrixCommandProperties properties, HystrixCommandMetrics metrics) {
// 从circuitBreakersByCommand缓存里取，key是CommandKey
HystrixCircuitBreaker previouslyCached = circuitBreakersByCommand.get(key.name());
if (previouslyCached != null) {
return previouslyCached;
}
// 缓存没有，创建一个放入缓存中
HystrixCircuitBreaker cbForCommand = circuitBreakersByCommand.putIfAbsent(key.name(), new HystrixCircuitBreakerImpl(key, group, properties, metrics));
if (cbForCommand == null) {
// this means the putIfAbsent step just created a new one so let's retrieve and return it
return circuitBreakersByCommand.get(key.name());
} else {
// this means a race occurred and while attempting to 'put' another one got there before
// and we instead retrieved it and will now return it
return cbForCommand;
}
}

hystrix - Fallback是怎么调用的提到了allowRequest方法，我们看看这里是做了哪些。

public boolean allowRequest() {
// 配置了强制熔断，直接返回false
if (properties.circuitBreakerForceOpen().get()) {
// properties have asked us to force the circuit open so we will allow NO requests
return false;
}
// 强制关闭
if (properties.circuitBreakerForceClosed().get()) {
// we still want to allow isOpen() to perform it's calculations so we simulate normal behavior
isOpen();
// properties have asked us to ignore errors so we will ignore the results of isOpen and just allow all traffic through
return true;
}
return !isOpen() || allowSingleTest();
}
public boolean isOpen() {
// 获取熔断器的状态，true就是开
if (circuitOpen.get()) {
// 如果是开的，还是返回ture，留给半开的时候用
return true;
}
// 如果是关的，获取HealthCounts信息
HealthCounts health = metrics.getHealthCounts();
// 当前的请求数如果小于设置的阈值，就直接返回false，说明没开
// 比如我们设置了20，此时才19，也是没有开的
// 这个值是样品数量的值，只有足够数量的样品，才比较准确
if (health.getTotalRequests() < properties.circuitBreakerRequestVolumeThreshold().get()) {
// we are not past the minimum volume threshold for the statisticalWindow so we'll return false immediately and not calculate anything
return false;
}
// 错误比例小于设定的值，比如错误的比例超过50%，就开启熔断
if (health.getErrorPercentage() < properties.circuitBreakerErrorThresholdPercentage().get()) {
return false;
} else {
// 这边设置时间，用于半开状态
if (circuitOpen.compareAndSet(false, true)) {
// if the previousValue was false then we want to set the currentTime
circuitOpenedOrLastTestedTime.set(System.currentTimeMillis());
return true;
} else {
// How could previousValue be true? If another thread was going through this code at the same time a race-condition could have
// caused another thread to set it to true already even though we were in the process of doing the same
// In this case, we know the circuit is open, so let the other thread set the currentTime and report back that the circuit is open
return true;
}
}
}

流程图如下：

半开状态

上面还有一个方法，allowSingleTest。这个是用于处理半开的时候。
我们上面知道，当熔断的时候，会保存一个值，circuitOpenedOrLastTestedTime。这个值加上设置的休眠时间和当前时间做比较，看看能不能允许尝试访问一次。

public boolean allowSingleTest() {
long timeCircuitOpenedOrWasLastTested = circuitOpenedOrLastTestedTime.get();
// 熔断器开的时候，并且当前时间>熔断时间+休眠时间
// 也就是说休眠时间设置为5，那5秒后给他一个机会看看能不能访问，也就是半开状态
// 然后重新设置circuitOpenedOrLastTestedTime
if (circuitOpen.get() && System.currentTimeMillis() > timeCircuitOpenedOrWasLastTested + properties.circuitBreakerSleepWindowInMilliseconds().get()) {
if (circuitOpenedOrLastTestedTime.compareAndSet(timeCircuitOpenedOrWasLastTested, System.currentTimeMillis())) {
return true;
}
}
return false;
}

HystrixCircuitBreaker创建

allowRequest是HystrixCircuitBreaker的方法，我们稍微回顾一下command的创建，AbstractCommand中，会调用initCircuitBreaker方法。他会通过HystrixCircuitBreaker的Factory来创建的

private static HystrixCircuitBreaker initCircuitBreaker(boolean enabled, HystrixCircuitBreaker fromConstructor,
HystrixCommandGroupKey groupKey, HystrixCommandKey commandKey,
HystrixCommandProperties properties, HystrixCommandMetrics metrics) {
if (enabled) {
if (fromConstructor == null) {
// get the default implementation of HystrixCircuitBreaker
return HystrixCircuitBreaker.Factory.getInstance(commandKey, groupKey, properties, metrics);
} else {
return fromConstructor;
}
} else {
return new NoOpCircuitBreaker();
}
}

在工厂中，他其实会通过缓存来获取的，也就是说每个CommandKey都有对应的HystrixCircuitBreaker。如果缓存没有，则创建一个放入缓存。

public static HystrixCircuitBreaker getInstance(HystrixCommandKey key, HystrixCommandGroupKey group, HystrixCommandProperties properties, HystrixCommandMetrics metrics) {
// 从circuitBreakersByCommand缓存里取，key是CommandKey
HystrixCircuitBreaker previouslyCached = circuitBreakersByCommand.get(key.name());
if (previouslyCached != null) {
return previouslyCached;
}
// 缓存没有，创建一个放入缓存中
HystrixCircuitBreaker cbForCommand = circuitBreakersByCommand.putIfAbsent(key.name(), new HystrixCircuitBreakerImpl(key, group, properties, metrics));
if (cbForCommand == null) {
// this means the putIfAbsent step just created a new one so let's retrieve and return it
return circuitBreakersByCommand.get(key.name());
} else {
// this means a race occurred and while attempting to 'put' another one got there before
// and we instead retrieved it and will now return it
return cbForCommand;
}
}

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