序
状态转换
- 闭->开
在设定的时间窗口内失败次数达到阈值，由闭->开。
- 开->半开
在处于开的状态，对目标的调用做失败返回，进入开的时候，启动计时器，设定时间过后进入半开状态。
- 半开->开
进入半开状态，会启动一个计数器，记录连续成功的调用次数，超过阈值，进入闭状态。有一次失败则进入开状态，同时清零连续成功调用次数。进入开的同时启动进入半开状态的定时器。
- 半开->闭
进入半开状态，会启动一个计数器，记录连续成功的调用次数，超过阈值，进入闭状态，同时清零连续成功调用次数。
实现要点
- 切到开状态启动的定时器
这里如果使用定时线程来做的话，开的线程多，管理比较麻烦，故这里改为维护一个切换到开状态的时间，在每次方法调用，判断是开状态时,判断是否已经过了这个超时阈值，超过的话，进入半开状态。
- 半开状态的计数器
目前半开状态没有使用时间窗口，仅仅使用连续成功次数来计算，一旦失败，则将断路器设置为open状态。如果连续成功次数达到阈值，则进入close状态。每次进入half-open的状态时，连续成功的计数器清零。
主要代码
断路器状态
public enum CircuitBreakerState {
CLOSED, // working normally, calls are transparently passing through
OPEN, // method calls are being intercepted and CircuitBreakerExceptions are being thrown instead
HALF_OPEN // method calls are passing through; if another blacklisted exception is thrown, reverts back to OPEN
}带时间窗口的计数器
/**
* 带时间窗口的限流计数器
*/
public class LimitCounter {
private long startTime;
private long timeIntervalInMs;
private int maxLimit;
private AtomicInteger currentCount;
public LimitCounter(long timeIntervalInMs, int maxLimit) {
super();
this.timeIntervalInMs = timeIntervalInMs;
this.maxLimit = maxLimit;
startTime = System.currentTimeMillis();
currentCount = new AtomicInteger(0);
}
public int incrAndGet() {
long currentTime = System.currentTimeMillis();
if ((startTime + timeIntervalInMs) < currentTime) {
synchronized (this) {
if ((startTime + timeIntervalInMs) < currentTime) {
startTime = currentTime;
currentCount.set(0);
}
}
}
return currentCount.incrementAndGet();
}
public boolean thresholdReached(){
return currentCount.get() > maxLimit;
}
public int get(){
return currentCount.get();
}
public /*synchronized*/ void reset(){
currentCount.set(0);
}
}主要配置
public class CircuitBreakerConfig {
//closed状态的失败次数阈值
private int failThreshold = 5;
//closed状态的失败计数的时间窗口
private int failCountWindowInMs = 60*1000;
//处于open状态下进入half-open的超时时间
private int open2HalfOpenTimeoutInMs = 5*1000;
//half-open状态下成功次数阈值
private int consecutiveSuccThreshold = 5;
private CircuitBreakerConfig(){
}
public static CircuitBreakerConfig newDefault(){
CircuitBreakerConfig config = new CircuitBreakerConfig();
return config;
}
public int getFailThreshold() {
return failThreshold;
}
public void setFailThreshold(int failThreshold) {
this.failThreshold = failThreshold;
}
public int getFailCountWindowInMs() {
return failCountWindowInMs;
}
public void setFailCountWindowInMs(int failCountWindowInMs) {
this.failCountWindowInMs = failCountWindowInMs;
}
public int getOpen2HalfOpenTimeoutInMs() {
return open2HalfOpenTimeoutInMs;
}
public void setOpen2HalfOpenTimeoutInMs(int open2HalfOpenTimeoutInMs) {
this.open2HalfOpenTimeoutInMs = open2HalfOpenTimeoutInMs;
}
public int getConsecutiveSuccThreshold() {
return consecutiveSuccThreshold;
}
public void setConsecutiveSuccThreshold(int consecutiveSuccThreshold) {
this.consecutiveSuccThreshold = consecutiveSuccThreshold;
}
}断路器
public class CircuitBreaker {
private static final Logger logger = LoggerFactory.getLogger(CircuitBreaker.class);
private String name;
private CircuitBreakerConfig config;
private volatile CircuitBreakerState state = CircuitBreakerState.CLOSED;
//最近进入open状态的时间
private volatile long lastOpenedTime;
//closed状态下失败次数
private LimitCounter failCount ;
//half-open状态的连续成功次数,失败立即清零
private AtomicInteger consecutiveSuccCount = new AtomicInteger(0);
//构造器
public CircuitBreaker(String name,CircuitBreakerConfig config) {
this.config = config;
this.name = name;
failCount = new LimitCounter(config.getFailCountWindowInMs(),config.getFailThreshold());
}
//状态判断
public boolean isOpen(){
return CircuitBreakerState.OPEN == state;
}
public boolean isHalfOpen(){
return CircuitBreakerState.HALF_OPEN == state;
}
public boolean isClosed(){
return CircuitBreakerState.CLOSED == state;
}
//状态操作
/**
* closed->open | halfopen -> open
*/
public void open(){
lastOpenedTime = System.currentTimeMillis();
state = CircuitBreakerState.OPEN;
logger.debug("circuit open,key:{}",name);
}
/**
* open -> halfopen
*/
public void openHalf(){
consecutiveSuccCount.set(0);
state = CircuitBreakerState.HALF_OPEN;
logger.debug("circuit open-half,key:{}",name);
}
/**
* halfopen -> close
*/
public void close(){
failCount.reset();
state = CircuitBreakerState.CLOSED;
logger.debug("circuit close,key:{}",name);
}
//阈值判断
/**
* 是否应该转到half open
* 前提是 open state
* @return
*/
public boolean isOpen2HalfOpenTimeout(){
return System.currentTimeMillis() - config.getOpen2HalfOpenTimeoutInMs() > lastOpenedTime;
}
/**
* 是否应该从close转到open
* @return
*/
public boolean isCloseFailThresholdReached(){
return failCount.thresholdReached();
}
/**
* half-open状态下是否达到close的阈值
* @return
*/
public boolean isConsecutiveSuccessThresholdReached(){
return consecutiveSuccCount.get() >= config.getConsecutiveSuccThreshold();
}
//getter
public void incrFailCount() {
int count = failCount.incrAndGet();
logger.debug("incr fail count:{},key:{}",count,name);
}
public AtomicInteger getConsecutiveSuccCount() {
return consecutiveSuccCount;
}
public CircuitBreakerState getState() {
return state;
}
}
断路器维护的变量
//最近进入open状态的时间
private volatile long lastOpenedTime;
//closed状态下失败次数
private LimitCounter failCount ;
//half-open状态的连续成功次数,失败立即清零
private AtomicInteger consecutiveSuccCount = new AtomicInteger(0);基于jdk代理的拦截
public class CircuitBreakerInvocationHandler implements InvocationHandler{
private static final Logger logger = LoggerFactory.getLogger(CircuitBreakerInvocationHandler.class);
private Object target;
public CircuitBreakerInvocationHandler(Object target) {
this.target = target;
}
//动态生成代理对象
public Object proxy(){
return Proxy.newProxyInstance(this.target.getClass().getClassLoader(), this.target.getClass().getInterfaces(), this);
}
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
GuardByCircuitBreaker breakerAnno = method.getAnnotation(GuardByCircuitBreaker.class);
if(breakerAnno == null){
return method.invoke(target,args);
}
Class[] noTripExs = breakerAnno.noTripExceptions();
int timeout = breakerAnno.timeoutInMs();
int interval = breakerAnno.failCountWindowInMs();
int failThreshold = breakerAnno.failThreshold();
CircuitBreakerConfig cfg = CircuitBreakerConfig.newDefault();
if(interval != -1){
cfg.setFailCountWindowInMs(interval);
}
if(failThreshold != -1){
cfg.setFailThreshold(failThreshold);
}
String key = target.getClass().getSimpleName() + method.getName();
CircuitBreaker breaker = CircuitBreakerRegister.get(key);
if(breaker == null){
breaker = new CircuitBreaker(key,cfg);
CircuitBreakerRegister.putIfAbsent(key,breaker);
}
Object returnValue = null;
logger.debug("breaker state:{},method:{}",breaker.getState(),method.toGenericString());
//breaker state
if(breaker.isOpen()){
//判断是否该进入half open状态
if(breaker.isOpen2HalfOpenTimeout()){
//进入half open状态
breaker.openHalf();
logger.debug("method:{} into half open",method.toGenericString());
returnValue = processHalfOpen(breaker,method,args,noTripExs);
}else{
throw new CircuitBreakerOpenException(method.toGenericString());
}
}else if(breaker.isClosed()){
try{
returnValue = method.invoke(target,args);
// 这里看情况是否重置标志
// breaker.close();
}catch (Throwable t){
if(isNoTripException(t,noTripExs)){
throw t;
}else{
//增加计数
breaker.incrFailCount();
if(breaker.isCloseFailThresholdReached()){
//触发阈值，打开
logger.debug("method:{} reached fail threshold, circuit breaker open",method.toGenericString());
breaker.open();
throw new CircuitBreakerOpenException(method.toGenericString());
}else{
throw t;
}
}
}
}else if(breaker.isHalfOpen()){
returnValue = processHalfOpen(breaker,method,args,noTripExs);
}
return returnValue;
}
private Object processHalfOpen(CircuitBreaker breaker,Method method, Object[] args,Class[] noTripExs) throws Throwable {
try{
Object returnValue = method.invoke(target,args);
breaker.getConsecutiveSuccCount().incrementAndGet();
if(breaker.isConsecutiveSuccessThresholdReached()){
//调用成功则进入close状态
breaker.close();
}
return returnValue;
}catch (Throwable t){
if(isNoTripException(t,noTripExs)){
breaker.getConsecutiveSuccCount().incrementAndGet();
if(breaker.isConsecutiveSuccessThresholdReached()){
breaker.close();
}
throw t;
}else{
breaker.open();
throw new CircuitBreakerOpenException(method.toGenericString(), t);
}
}
}
private boolean isNoTripException(Throwable t,Class[] noTripExceptions){
if(noTripExceptions == null || noTripExceptions.length == 0){
return false;
}
for(Class ex:noTripExceptions){
//是否是抛出异常t的父类
//t java.lang.reflect.InvocationTargetException
if(ex.isAssignableFrom(t.getCause().getClass())){
return true;
}
}
return false;
}
}github工程 circuit-breaker
参考
- martinfowler-CircuitBreaker
- microsoft-Circuit Breaker Pattern(
必读) - cloud-design-patterns-断路器模式
- HystrixCircuitBreaker
- 熔断器设计模式(
实现参考) - Creating a circuit breaker with Spring AOP(
实现参考) - alenegro81/CircuitBreaker(
参考jdk代理实现)