流控神器Sentinel指南：熔断降级源码分析

1
2
3
4
5
6
7
8
9
10
11
@Override
public void entry(Context context, ResourceWrapper resourceWrapper, DefaultNode node, int count, boolean prioritized, Object... args)
throws Throwable {
DegradeRuleManager.checkDegrade(resourceWrapper, context, node, count);
fireEntry(context, resourceWrapper, node, count, prioritized, args);
}
@Override
public void exit(Context context, ResourceWrapper resourceWrapper, int count, Object... args) {
fireExit(context, resourceWrapper, count, args);
}

1
2
3
4
5
6
7
8
9
10
11
12
13
14
 public static void checkDegrade(ResourceWrapper resource, Context context, DefaultNode node, int count)
throws BlockException {
// degradeRules保存了所有的熔断规则，key为ResourceName，value为 Set<DegradeRule> 
Set<DegradeRule> rules = degradeRules.get(resource.getName());
if (rules == null) {// 如果没有设置规则，那么直接返回
return;
}
for (DegradeRule rule : rules) {
if (!rule.passCheck(context, node, count)) {
throw new DegradeException(rule.getLimitApp(), rule);
}
}
}

1
2
3
4
5
6
7
8
private int grade
private double count;
private int timeWindow;
private final AtomicBoolean cut = new AtomicBoolean(false);
private AtomicLong passCount = new AtomicLong(0);
private static ScheduledExecutorService pool = Executors.newScheduledThreadPool(
Runtime.getRuntime().availableProcessors(), new NamedThreadFactory("sentinel-degrade-reset-task", true));

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
 @Override
public boolean passCheck(Context context, DefaultNode node, int acquireCount, Object... args) {
if (cut.get()) {// cut是AtomicBoolean类型，默认false
return false;
}
// 获取到该资源对应的ClusterNode
ClusterNode clusterNode = ClusterBuilderSlot.getClusterNode(this.getResource());
if (clusterNode == null) {
return true;
}
// 下面是三种降级策略
if (grade == RuleConstant.DEGRADE_GRADE_RT) {
double rt = clusterNode.avgRt();
if (rt < this.count) {
passCount.set(0);
return true;
}
if (passCount.incrementAndGet() < RT_MAX_EXCEED_N) {
return true;
}
} else if (grade == RuleConstant.DEGRADE_GRADE_EXCEPTION_RATIO) {
double exception = clusterNode.exceptionQps();
double success = clusterNode.successQps();
double total = clusterNode.totalQps();
// if total qps less than RT_MAX_EXCEED_N, pass.
if (total < RT_MAX_EXCEED_N) {
return true;
}
double realSuccess = success - exception;
if (realSuccess <= 0 && exception < RT_MAX_EXCEED_N) {
return true;
}
if (exception / success < count) {
return true;
}
} else if (grade == RuleConstant.DEGRADE_GRADE_EXCEPTION_COUNT) {
double exception = clusterNode.totalException();
if (exception < count) {
return true;
}
}
if (cut.compareAndSet(false, true)) {
ResetTask resetTask = new ResetTask(this);
pool.schedule(resetTask, timeWindow, TimeUnit.SECONDS);
}
return false;
}