21、SpringCloud Alibaba - Sentinel服务熔断降级DegradeSlot
一、DegradeRule
/**
* 降级策略：慢调用比例、异常比例、异常数
*/
private int grade = RuleConstant.DEGRADE_GRADE_RT;
/**
* 阈值：最大RT、比例阈值、异常数
*/
private double count;
/**
* 降级恢复时间，多久后结束降级
*/
private int timeWindow;
/**
* 触达熔断的最小请求数量
*/
private int minRequestAmount = RuleConstant.DEGRADE_DEFAULT_MIN_REQUEST_AMOUNT;
/**
* RT 模式的慢比例阈值
*/
private double slowRatioThreshold = 1.0d;
/**
* 统计时长
*/
private int statIntervalMs = 1000;
一、DegradeSlot
1、 entry()；
在entry方法中，对熔断规则的状态进行判断，CLOSE 状态通过规则，OPEN 状态时检验熔断时间是否已经过去，如果过去了则更新状态为 HALF_OPEN。
·1、、entry( )
@Override
public void entry(Context context, ResourceWrapper resourceWrapper, DefaultNode node, int count,
boolean prioritized, Object... args) throws Throwable {
//执行熔断规则检查
performChecking(context, resourceWrapper);
//下一个节点
fireEntry(context, resourceWrapper, node, count, prioritized, args);
}
2、、performChecking( )
void performChecking(Context context, ResourceWrapper r) throws BlockException {
//获取该资源的熔断规则
List<CircuitBreaker> circuitBreakers = DegradeRuleManager.getCircuitBreakers(r.getName());
if (circuitBreakers == null || circuitBreakers.isEmpty()) {
return;
}
for (CircuitBreaker cb : circuitBreakers) {
//规则检验
if (!cb.tryPass(context)) {
throw new DegradeException(cb.getRule().getLimitApp(), cb.getRule());
}
}
}
3、、tryPass( )
@Override
public boolean tryPass(Context context) {
// Template implementation.
//熔断处于关闭状态，返回成功
if (currentState.get() == State.CLOSED) {
return true;
}
//熔断处于打开状态
if (currentState.get() == State.OPEN) {
// For half-open state we allow a request for probing.
//校验降级时间是否已经过了，从打开状态转换成半开状态
return retryTimeoutArrived() && fromOpenToHalfOpen(context);
}
return false;
}
4、、retryTimeoutArrived( )
protected boolean retryTimeoutArrived() {
return TimeUtil.currentTimeMillis() >= nextRetryTimestamp;
}
5、、fromOpenToHalfOpen( )
protected boolean fromOpenToHalfOpen(Context context) {
//更新状态，由 OPEN 到 HALF_OPEN
if (currentState.compareAndSet(State.OPEN, State.HALF_OPEN)) {
//通知观察者状态变化
notifyObservers(State.OPEN, State.HALF_OPEN, null);
Entry entry = context.getCurEntry();
//注册exitHandlers，在执行链 Slot chain 执行完退出后，会回调exitHandlers
entry.whenTerminate(new BiConsumer<Context, Entry>() {
@Override
public void accept(Context context, Entry entry) {
// Note: This works as a temporary workaround for https://github.com/alibaba/Sentinel/issues/1638
// Without the hook, the circuit breaker won't recover from half-open state in some circumstances
// when the request is actually blocked by upcoming rules (not only degrade rules).
//如果出现了BlockException
if (entry.getBlockError() != null) {
// Fallback to OPEN due to detecting request is blocked
//将状态恢复，由 HALF_OPEN 到 OPEN
currentState.compareAndSet(State.HALF_OPEN, State.OPEN);
//通知监听者
notifyObservers(State.HALF_OPEN, State.OPEN, 1.0d);
}
}
});
return true;
}
return false;
}
2、 exit()；
public void exit(Context context, ResourceWrapper r, int count, Object... args) {
Entry curEntry = context.getCurEntry();
//出现异常，直接执行下一个节点
if (curEntry.getBlockError() != null) {
fireExit(context, r, count, args);
return;
}
List<CircuitBreaker> circuitBreakers = DegradeRuleManager.getCircuitBreakers(r.getName());
//没有熔断规则，直接执行下一个节点
if (circuitBreakers == null || circuitBreakers.isEmpty()) {
fireExit(context, r, count, args);
return;
}
if (curEntry.getBlockError() == null) {
// passed request
for (CircuitBreaker circuitBreaker : circuitBreakers) {
//调用每一个熔断规则的 onRequestComplete，分别有ResponseTimeCircuitBreaker、ExceptionCircuitBreaker
circuitBreaker.onRequestComplete(context);
}
}
//执行下一个节点
fireExit(context, r, count, args);
}
三、ResponseTimeCircuitBreaker
慢调用比例的处理逻辑，时间窗口使用的是SlowRequestLeapArray ，对应的bucket是 SlowRequestCounter
1、 SlowRequestLeapArray；
static class SlowRequestLeapArray extends LeapArray<SlowRequestCounter> {
public SlowRequestLeapArray(int sampleCount, int intervalInMs) {
super(sampleCount, intervalInMs);
}
@Override
public SlowRequestCounter newEmptyBucket(long timeMillis) {
return new SlowRequestCounter();
}
@Override
protected WindowWrap<SlowRequestCounter> resetWindowTo(WindowWrap<SlowRequestCounter> w, long startTime) {
w.resetTo(startTime);
w.value().reset();
return w;
}
}
2、 SlowRequestCounter；
static class SlowRequestCounter {
private LongAdder slowCount;
private LongAdder totalCount;
public SlowRequestCounter() {
//慢请求数量
this.slowCount = new LongAdder();
//总请求数量
this.totalCount = new LongAdder();
}
public LongAdder getSlowCount() {
return slowCount;
}
public LongAdder getTotalCount() {
return totalCount;
}
public SlowRequestCounter reset() {
slowCount.reset();
totalCount.reset();
return this;
}
@Override
public String toString() {
return "SlowRequestCounter{" +
"slowCount=" + slowCount +
", totalCount=" + totalCount +
'}';
}
}
3、 onRequestComplete()；
public void onRequestComplete(Context context) {
//当前时间窗口的慢请求计数器
SlowRequestCounter counter = slidingCounter.currentWindow().value();
Entry entry = context.getCurEntry();
if (entry == null) {
return;
}
long completeTime = entry.getCompleteTimestamp();
if (completeTime <= 0) {
completeTime = TimeUtil.currentTimeMillis();
}
//计算响应时间
long rt = completeTime - entry.getCreateTimestamp();
//大于阈值，为慢请求
if (rt > maxAllowedRt) {
counter.slowCount.add(1);
}
//总数量也加1
counter.totalCount.add(1);
//处理熔断规则状态
handleStateChangeWhenThresholdExceeded(rt);
}
4、 handleStateChangeWhenThresholdExceeded()；
private void handleStateChangeWhenThresholdExceeded(long rt) {
//已经是打开状态
if (currentState.get() == State.OPEN) {
return;
}
//半开状态
if (currentState.get() == State.HALF_OPEN) {
// In detecting request
// TODO: improve logic for half-open recovery
if (rt > maxAllowedRt) {
//熔断时间过去后的下一次请求处于半开状态，此时又超时了，直接由半开变为打开
fromHalfOpenToOpen(1.0d);
} else {
//没有超时，由半开变为关闭
fromHalfOpenToClose();
}
return;
}
//获取窗口计数器
List<SlowRequestCounter> counters = slidingCounter.values();
long slowCount = 0;
long totalCount = 0;
for (SlowRequestCounter counter : counters) {
//慢请求数量
slowCount += counter.slowCount.sum();
//总请求数量
totalCount += counter.totalCount.sum();
}
//总数量 达不到 触达熔断的最小请求数量
if (totalCount < minRequestAmount) {
return;
}
//慢请求比例
double currentRatio = slowCount * 1.0d / totalCount;
if (currentRatio > maxSlowRequestRatio) {
//打开熔断
transformToOpen(currentRatio);
}
}
5、 transformToOpen()；
protected void transformToOpen(double triggerValue) {
State cs = currentState.get();
switch (cs) {
case CLOSED:
fromCloseToOpen(triggerValue);
break;
case HALF_OPEN:
fromHalfOpenToOpen(triggerValue);
break;
default:
break;
}
}
6、 fromCloseToOpen()；
状态由Close 到 Open
protected boolean fromCloseToOpen(double snapshotValue) {
State prev = State.CLOSED;
if (currentState.compareAndSet(prev, State.OPEN)) {
//更新熔断结束时间
updateNextRetryTimestamp();
//通知状态变化
notifyObservers(prev, State.OPEN, snapshotValue);
return true;
}
return false;
}
protected void updateNextRetryTimestamp() {
//当前时间加上熔断恢复时间
this.nextRetryTimestamp = TimeUtil.currentTimeMillis() + recoveryTimeoutMs;
}
7、 fromHalfOpenToOpen()；
状态由HALF_OPEN 到 Open
protected boolean fromHalfOpenToOpen(double snapshotValue) {
if (currentState.compareAndSet(State.HALF_OPEN, State.OPEN)) {
updateNextRetryTimestamp();
notifyObservers(State.HALF_OPEN, State.OPEN, snapshotValue);
return true;
}
return false;
}
8、 fromHalfOpenToClose()；
状态由HALF_OPEN 到 Close
protected boolean fromHalfOpenToClose() {
if (currentState.compareAndSet(State.HALF_OPEN, State.CLOSED)) {
//重置统计指标
resetStat();
notifyObservers(State.HALF_OPEN, State.CLOSED, null);
return true;
}
return false;
}
public void resetStat() {
// Reset current bucket (bucket count = 1).
slidingCounter.currentWindow().value().reset();
}
public SlowRequestCounter reset() {
slowCount.reset();
totalCount.reset();
return this;
}
四、ExceptionCircuitBreaker
异常比例、异常数 熔断规则的处理逻辑，时间窗口使用的是SimpleErrorCounterLeapArray，对应的bucket是 SimpleErrorCounter
1、 SimpleErrorCounterLeapArray；
static class SimpleErrorCounterLeapArray extends LeapArray<SimpleErrorCounter> {
public SimpleErrorCounterLeapArray(int sampleCount, int intervalInMs) {
super(sampleCount, intervalInMs);
}
@Override
public SimpleErrorCounter newEmptyBucket(long timeMillis) {
return new SimpleErrorCounter();
}
@Override
protected WindowWrap<SimpleErrorCounter> resetWindowTo(WindowWrap<SimpleErrorCounter> w, long startTime) {
// Update the start time and reset value.
w.resetTo(startTime);
w.value().reset();
return w;
}
}
2、 SimpleErrorCounter；
static class SimpleErrorCounter {
//异常数量
private LongAdder errorCount;
//总数量
private LongAdder totalCount;
public SimpleErrorCounter() {
this.errorCount = new LongAdder();
this.totalCount = new LongAdder();
}
public LongAdder getErrorCount() {
return errorCount;
}
public LongAdder getTotalCount() {
return totalCount;
}
public SimpleErrorCounter reset() {
errorCount.reset();
totalCount.reset();
return this;
}
@Override
public String toString() {
return "SimpleErrorCounter{" +
"errorCount=" + errorCount +
", totalCount=" + totalCount +
'}';
}
}
3、 onRequestComplete()；
public void onRequestComplete(Context context) {
Entry entry = context.getCurEntry();
if (entry == null) {
return;
}
Throwable error = entry.getError();
//当前时间窗口的慢请求计数器
SimpleErrorCounter counter = stat.currentWindow().value();
//有异常时，异常数量加1
if (error != null) {
counter.getErrorCount().add(1);
}
//总数量加1
counter.getTotalCount().add(1);
//处理熔断状态变化
handleStateChangeWhenThresholdExceeded(error);
}
4、 handleStateChangeWhenThresholdExceeded()；
private void handleStateChangeWhenThresholdExceeded(Throwable error) {
//打开状态
if (currentState.get() == State.OPEN) {
return;
}
//半开状态
if (currentState.get() == State.HALF_OPEN) {
// In detecting request
if (error == null) {
//没有异常，由半开变为关闭
fromHalfOpenToClose();
} else {
//有异常，由半开变为打开
fromHalfOpenToOpen(1.0d);
}
return;
}
//关闭状态
//获取时间窗口异常计数器
List<SimpleErrorCounter> counters = stat.values();
long errCount = 0;
long totalCount = 0;
for (SimpleErrorCounter counter : counters) {
//异常总数
errCount += counter.errorCount.sum();
//请求总数
totalCount += counter.totalCount.sum();
}
//总数小于触达熔断的最小请求数量
if (totalCount < minRequestAmount) {
return;
}
double curCount = errCount;
if (strategy == DEGRADE_GRADE_EXCEPTION_RATIO) {
// Use errorRatio
//异常比例
curCount = errCount * 1.0d / totalCount;
}
//比较异常比例或者比较异常数
if (curCount > threshold) {
//打开熔断，跟ResponseTimeCircuitBreaker一样调用父类AbstractCircuitBreaker的方法
transformToOpen(curCount);
}
}