Circuit breaker hystrixcircuitbreaker

package com.netflix.hystrix;

import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.AtomicReference;

import com.netflix.hystrix.HystrixCommandMetrics.HealthCounts;
import rx.Subscriber;
import rx.Subscription;

public interface HystrixCircuitBreaker {

    boolean allowRequest();
    
    boolean isOpen();

    void markSuccess();

    void markNonSuccess();

    boolean attemptExecution();

    class Factory {
        // String is HystrixCommandKey.name() (we can't use HystrixCommandKey directly as we can't guarantee it implements hashcode/equals correctly)
        private static ConcurrentHashMap<String, HystrixCircuitBreaker> circuitBreakersByCommand = new ConcurrentHashMap<String, HystrixCircuitBreaker>();
    }


    class HystrixCircuitBreakerImpl implements HystrixCircuitBreaker {
    }

    static class NoOpCircuitBreaker implements HystrixCircuitBreaker {
    }

}

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Let's take a look at the abstract methods of this interface ：

allowRequest(): Every Hystrix The request of the command is judged to be executed by it ( No longer in use , Use attemptExecution() Method to judge ) attemptExecution(): Every Hystrix The request of the command is judged to be executed by it isOpen(): Returns whether the current circuit breaker is open markSuccess(): Used to close the circuit breaker markNonSuccess: Used to open the circuit breaker

Let's take a look at the classes in this interface :

Factory: One was maintained Hystrix Command and HystrixCircuitBreaker Collection of relationships for ConcurrentHashMap<String, HystrixCircuitBreaker> circuitBreakersByCommand. among key adopt HystrixCommandKey To define , every last Hystrix Commands need to have one Key To mark , At the same time, according to this Key The corresponding circuit breaker instance can be found . NoOpCircuitBreaker: A circuit breaker that does nothing , It allows all requests to pass , And the circuit breaker is always closed HystrixCircuitBreakerImpl: Another implementation class for circuit breakers .

HystrixCircuitBreakerImpl Introduce

Five core objects of circuit breaker are defined in this class :

HystrixCommandProperties properties: The attribute collection object of the corresponding instance of the circuit breaker / The circuit breaker corresponds to HystrixCommand The property object of the instance HystrixCommandMetrics metrics: Used to make HystrixCommand Record the objects of various metrics AtomicReference<Status> status: Used to record the status of the circuit breaker , The default is off AtomicLong circuitOpened: Time stamp of circuit breaker opening , Default -1, Indicates that the circuit breaker is not open AtomicReference<Subscription> activeSubscription: Record HystrixCommand

The implementation of the interface is as follows ：

        @Override
        public boolean isOpen() {
            if (properties.circuitBreakerForceOpen().get()) {
                return true;
            }
            if (properties.circuitBreakerForceClosed().get()) {
                return false;
            }
            return circuitOpened.get() >= 0;
        }

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Used to judge whether the circuit breaker is open or closed . The main steps are ：

If the circuit breaker is forced open , return true If the circuit breaker is forced to close , return false Judge circuitOpened Value , If greater than or equal to 0, return true, Otherwise return to false

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