Sentinel 笔记

    // ResourceType represents classification of the resources
    type ResourceType int32

    const (
        ResTypeCommon ResourceType = iota
        ResTypeWeb
        ResTypeRPC
    )

    // TrafficType describes the traffic type: Inbound or Outbound
    type TrafficType int32

    const (
        // Inbound represents the inbound traffic (e.g. provider)
        Inbound TrafficType = iota
        // Outbound represents the outbound traffic (e.g. consumer)
        Outbound
    )

    // ResourceWrapper represents the invocation
    type ResourceWrapper struct {
        // global unique resource name
        name string
        // resource classification
        classification ResourceType
        // Inbound or Outbound
        flowType TrafficType
    }

    // EntryOptions represents the options of a Sentinel resource entry.
    type EntryOptions struct {
        resourceType base.ResourceType
        entryType    base.TrafficType
        acquireCount uint32
        slotChain    *base.SlotChain
    }

    type EntryContext struct {
        entry *SentinelEntry

        // Use to calculate RT
        startTime uint64

        Resource *ResourceWrapper
        StatNode StatNode

        Input *SentinelInput
        // the result of rule slots check
        RuleCheckResult *TokenResult
    }

    type SentinelEntry struct {
        res *ResourceWrapper
        // one entry bounds with one context
        ctx *EntryContext

        sc *SlotChain
    }

    type TokenCalculateStrategy int32
    const (
        Direct TokenCalculateStrategy = iota
        WarmUp
    )

    type ControlBehavior int32
    const (
        Reject ControlBehavior = iota
        Throttling
    )

    // Rule describes the strategy of flow control, the flow control strategy is based on QPS statistic metric
    type Rule struct {
        // Resource represents the resource name.
        Resource               string                 `json:"resource"`
        ControlBehavior        ControlBehavior        `json:"controlBehavior"`
        // Threshold means the threshold during StatIntervalInMs
        // If StatIntervalInMs is 1000(1 second), Threshold means QPS
        Threshold         float64          `json:"threshold"`
        MaxQueueingTimeMs uint32           `json:"maxQueueingTimeMs"`
        // StatIntervalInMs indicates the statistic interval and it's the optional setting for flow Rule.
        // If user doesn't set StatIntervalInMs, that means using default metric statistic of resource.
        // If the StatIntervalInMs user specifies can not reuse the global statistic of resource,
        //      sentinel will generate independent statistic structure for this rule.
        StatIntervalInMs uint32 `json:"statIntervalInMs"`
    }

    // core/flow/traffic_shaping.go

    // TrafficShapingCalculator calculates the actual traffic shaping threshold
    // based on the threshold of rule and the traffic shaping strategy.
    type TrafficShapingCalculator interface {
        CalculateAllowedTokens(acquireCount uint32, flag int32) float64
    }

    type DirectTrafficShapingCalculator struct {
        threshold float64
    }

    func (d *DirectTrafficShapingCalculator) CalculateAllowedTokens(uint32, int32) float64 {
        return d.threshold
    }

    // TrafficShapingChecker performs checking according to current metrics and the traffic
    // shaping strategy, then yield the token result.
    type TrafficShapingChecker interface {
        DoCheck(resStat base.StatNode, acquireCount uint32, threshold float64) *base.TokenResult
    }

    type RejectTrafficShapingChecker struct {
        rule  *Rule
    }

    func (d *RejectTrafficShapingChecker) DoCheck(resStat base.StatNode, acquireCount uint32, threshold float64) *base.TokenResult {
        metricReadonlyStat := d.BoundOwner().boundStat.readOnlyMetric
        if metricReadonlyStat == nil {
            return nil
        }
        curCount := float64(metricReadonlyStat.GetSum(base.MetricEventPass))
        if curCount+float64(acquireCount) > threshold {
            return base.NewTokenResultBlockedWithCause(base.BlockTypeFlow, "", d.rule, curCount)
        }
        return nil
    }

    type TrafficShapingController struct {
        flowCalculator TrafficShapingCalculator
        flowChecker    TrafficShapingChecker

        rule *Rule
        // boundStat is the statistic of current TrafficShapingController
        boundStat standaloneStatistic
    }

    func (t *TrafficShapingController) PerformChecking(acquireCount uint32, flag int32) *base.TokenResult {
        allowedTokens := t.flowCalculator.CalculateAllowedTokens(acquireCount, flag)
        return t.flowChecker.DoCheck(resStat, acquireCount, allowedTokens)
    }

   // TrafficControllerMap represents the map storage for TrafficShapingController.
   type TrafficControllerMap map[string][]*TrafficShapingController
    // core/flow/rule_manager.go
    tcMap        = make(TrafficControllerMap)

    func generateStatFor(rule *Rule) (*standaloneStatistic, error) {
        resNode = stat.GetOrCreateResourceNode(rule.Resource, base.ResTypeCommon)

        // default case, use the resource's default statistic
        readStat := resNode.DefaultMetric()
        retStat.reuseResourceStat = true
        retStat.readOnlyMetric = readStat
        retStat.writeOnlyMetric = nil
        return &retStat, nil
    }   

    // BucketWrap represent a slot to record metrics
    // In order to reduce the usage of memory, BucketWrap don't hold length of BucketWrap
    // The length of BucketWrap could be seen in LeapArray.
    // The scope of time is [startTime, startTime+bucketLength)
    // The size of BucketWrap is 24(8+16) bytes
    type BucketWrap struct {
        // The start timestamp of this statistic bucket wrapper.
        BucketStart uint64
        // The actual data structure to record the metrics (e.g. MetricBucket).
        Value atomic.Value
    }

      // core/circuitbreaker/circuit_breaker.go
    type slowRequestCounter struct {
        slowCount  uint64
        totalCount uint64
    }

    // core/circuitbreaker/circuit_breaker.go
    type errorCounter struct {
        errorCount uint64
        totalCount uint64
    }

    // MetricBucket represents the entity to record metrics per minimum time unit (i.e. the bucket time span).
    // Note that all operations of the MetricBucket are required to be thread-safe.
    type MetricBucket struct {
        // Value of statistic
        counter [base.MetricEventTotal]int64
        minRt   int64
    }

    // There are five events to record
    // pass + block == Total
    const (
        // sentinel rules check pass
        MetricEventPass MetricEvent = iota
        // sentinel rules check block
        MetricEventBlock

        MetricEventComplete
        // Biz error, used for circuit breaker
        MetricEventError
        // request execute rt, unit is millisecond
        MetricEventRt
        // hack for the number of event
        MetricEventTotal
    )

    // atomic BucketWrap array to resolve race condition
    // AtomicBucketWrapArray can not append or delete element after initializing
    type AtomicBucketWrapArray struct {
        // The base address for real data array
        base unsafe.Pointer
        // The length of slice(array), it can not be modified.
        length int
        data   []*BucketWrap
    }

    // Give a diagram to illustrate
    // Suppose current time is 888, bucketLengthInMs is 200ms,
    // intervalInMs is 1000ms, LeapArray will build the below windows
    //   B0       B1      B2     B3      B4
    //   |_______|_______|_______|_______|_______|
    //  1000    1200    1400    1600    800    (1000)
    //                                        ^
    //                                      time=888
    type LeapArray struct {
        bucketLengthInMs uint32
        sampleCount      uint32
        intervalInMs     uint32
        array            *AtomicBucketWrapArray
        // update lock
        updateLock mutex
    }

    func (la *LeapArray) currentBucketOfTime(now uint64, bg BucketGenerator) (*BucketWrap, error) {
        if now <= 0 {
            return nil, errors.New("Current time is less than 0.")
        }

        idx := la.calculateTimeIdx(now)
        bucketStart := calculateStartTime(now, la.bucketLengthInMs)

        for { //spin to get the current BucketWrap
            old := la.array.get(idx)
            if old == nil {
                // because la.array.data had initiated when new la.array
                // theoretically, here is not reachable
                newWrap := &BucketWrap{
                    BucketStart: bucketStart,
                    Value:       atomic.Value{},
                }
                newWrap.Value.Store(bg.NewEmptyBucket())
                if la.array.compareAndSet(idx, nil, newWrap) {
                    return newWrap, nil
                } else {
                    runtime.Gosched()
                }
            } else if bucketStart == atomic.LoadUint64(&old.BucketStart) {
                return old, nil
            } else if bucketStart > atomic.LoadUint64(&old.BucketStart) {
                // current time has been next cycle of LeapArray and LeapArray dont't count in last cycle.
                // reset BucketWrap
                if la.updateLock.TryLock() {
                    old = bg.ResetBucketTo(old, bucketStart)
                    la.updateLock.Unlock()
                    return old, nil
                } else {
                    runtime.Gosched()
                }
            } else if bucketStart < atomic.LoadUint64(&old.BucketStart) {
                // TODO: reserve for some special case (e.g. when occupying "future" buckets).
                return nil, errors.New(fmt.Sprintf("Provided time timeMillis=%d is already behind old.BucketStart=%d.", bucketStart, old.BucketStart))
            }
        }
    }

    // The implementation of sliding window based on LeapArray (as the sliding window infrastructure)
    // and MetricBucket (as the data type). The MetricBucket is used to record statistic
    // metrics per minimum time unit (i.e. the bucket time span).
    type BucketLeapArray struct {
        data     LeapArray
        dataType string
    }

    // SlidingWindowMetric represents the sliding window metric wrapper.
    // It does not store any data and is the wrapper of BucketLeapArray to adapt to different internal bucket
    // SlidingWindowMetric is used for SentinelRules and BucketLeapArray is used for monitor
    // BucketLeapArray is per resource, and SlidingWindowMetric support only read operation.
    type SlidingWindowMetric struct {
        bucketLengthInMs uint32
        sampleCount      uint32
        intervalInMs     uint32
        real             *BucketLeapArray
    }

    type BaseStatNode struct {
        sampleCount uint32
        intervalMs  uint32

        goroutineNum int32

        arr    *sbase.BucketLeapArray
        metric *sbase.SlidingWindowMetric
    }

    type ResourceNode struct {
        BaseStatNode

        resourceName string
        resourceType base.ResourceType
    }

    // core/stat/node_storage.go
    type ResourceNodeMap map[string]*ResourceNode
    var (
        inboundNode = NewResourceNode(base.TotalInBoundResourceName, base.ResTypeCommon)

        resNodeMap = make(ResourceNodeMap)
        rnsMux     = new(sync.RWMutex)
    )

    // StatPrepareSlot is responsible for some preparation before statistic
    // For example: init structure and so on
    type StatPrepareSlot interface {
        // Prepare function do some initialization
        // Such as: init statistic structure、node and etc
        // The result of preparing would store in EntryContext
        // All StatPrepareSlots execute in sequence
        // Prepare function should not throw panic.
        Prepare(ctx *EntryContext)
    }

    // RuleCheckSlot is rule based checking strategy
    // All checking rule must implement this interface.
    type RuleCheckSlot interface {
        // Check function do some validation
        // It can break off the slot pipeline
        // Each TokenResult will return check result
        // The upper logic will control pipeline according to SlotResult.
        Check(ctx *EntryContext) *TokenResult
    }

    // StatSlot is responsible for counting all custom biz metrics.
    // StatSlot would not handle any panic, and pass up all panic to slot chain
    type StatSlot interface {
        // OnEntryPass function will be invoked when StatPrepareSlots and RuleCheckSlots execute pass
        // StatSlots will do some statistic logic, such as QPS、log、etc
        OnEntryPassed(ctx *EntryContext)
        // OnEntryBlocked function will be invoked when StatPrepareSlots and RuleCheckSlots fail to execute
        // It may be inbound flow control or outbound cir
        // StatSlots will do some statistic logic, such as QPS、log、etc
        // blockError introduce the block detail
        OnEntryBlocked(ctx *EntryContext, blockError *BlockError)
        // OnCompleted function will be invoked when chain exits.
        // The semantics of OnCompleted is the entry passed and completed
        // Note: blocked entry will not call this function
        OnCompleted(ctx *EntryContext)
    }

    // core/base/slot_chain.go
    // StatPrepareSlot is responsible for some preparation before statistic
    // For example: init structure and so on
    type StatPrepareSlot interface {
        // Prepare function do some initialization
        // Such as: init statistic structure、node and etc
        // The result of preparing would store in EntryContext
        // All StatPrepareSlots execute in sequence
        // Prepare function should not throw panic.
        Prepare(ctx *EntryContext)
    }

    // core/stat/stat_prepare_slot.go
    type ResourceNodePrepareSlot struct {
    }

    func (s *ResourceNodePrepareSlot) Prepare(ctx *base.EntryContext) {
        node := GetOrCreateResourceNode(ctx.Resource.Name(), ctx.Resource.Classification())
        // Set the resource node to the context.
        ctx.StatNode = node
    }

    type Slot struct {
    }

    func (s *Slot) Check(ctx *base.EntryContext) *base.TokenResult {
        res := ctx.Resource.Name()
        tcs := getTrafficControllerListFor(res)
        result := ctx.RuleCheckResult

        // Check rules in order
        for _, tc := range tcs {
            r := canPassCheck(tc, ctx.StatNode, ctx.Input.AcquireCount)
            if r == nil {
                // nil means pass
                continue
            }
            if r.Status() == base.ResultStatusBlocked {
                return r
            }
            if r.Status() == base.ResultStatusShouldWait {
                if waitMs := r.WaitMs(); waitMs > 0 {
                    // Handle waiting action.
                    time.Sleep(time.Duration(waitMs) * time.Millisecond)
                }
                continue
            }
        }
        return result
    }

    func canPassCheck(tc *TrafficShapingController, node base.StatNode, acquireCount uint32) *base.TokenResult {
        return canPassCheckWithFlag(tc, node, acquireCount, 0)
    }

    func canPassCheckWithFlag(tc *TrafficShapingController, node base.StatNode, acquireCount uint32, flag int32) *base.TokenResult {
        return checkInLocal(tc, node, acquireCount, flag)
    }

    func checkInLocal(tc *TrafficShapingController, resStat base.StatNode, acquireCount uint32, flag int32) *base.TokenResult {
        return tc.PerformChecking(resStat, acquireCount, flag)
    }

    // core/flow/standalone_stat_slot.go
    type StandaloneStatSlot struct {
    }

    func (s StandaloneStatSlot) OnEntryPassed(ctx *base.EntryContext) {
        res := ctx.Resource.Name()
        for _, tc := range getTrafficControllerListFor(res) {
            if !tc.boundStat.reuseResourceStat {
                if tc.boundStat.writeOnlyMetric != nil {
                    tc.boundStat.writeOnlyMetric.AddCount(base.MetricEventPass, int64(ctx.Input.AcquireCount))
                }
            }
        }
    }

    func (s StandaloneStatSlot) OnEntryBlocked(ctx *base.EntryContext, blockError *base.BlockError) {
        // Do nothing
    }

    func (s StandaloneStatSlot) OnCompleted(ctx *base.EntryContext) {
        // Do nothing
    }

    // core/base/slot_chain.go
    type SlotChain struct {
    }

    func (sc *SlotChain) exit(ctx *EntryContext) {
        // The OnCompleted is called only when entry passed
        if ctx.IsBlocked() {
            return
        }
        for _, s := range sc.stats {
            s.OnCompleted(ctx)
        }
    }

    // core/base/entry.go
    type SentinelEntry struct {
        sc *SlotChain
        exitCtl sync.Once
    }

    func (e *SentinelEntry) Exit() {
        e.exitCtl.Do(func() {
            if e.sc != nil {
                e.sc.exit(ctx)
            }
        })
    }

   // core/base/slot_chain.go

    // SlotChain hold all system slots and customized slot.
    // SlotChain support plug-in slots developed by developer.
    type SlotChain struct {
        statPres   []StatPrepareSlot
        ruleChecks []RuleCheckSlot
        stats      []StatSlot
    }

    // The entrance of slot chain
    // Return the TokenResult and nil if internal panic.
    func (sc *SlotChain) Entry(ctx *EntryContext) *TokenResult {
        // execute prepare slot
        sps := sc.statPres
        if len(sps) > 0 {
            for _, s := range sps {
                s.Prepare(ctx)
            }
        }

        // execute rule based checking slot
        rcs := sc.ruleChecks
        var ruleCheckRet *TokenResult
        if len(rcs) > 0 {
            for _, s := range rcs {
                sr := s.Check(ctx)
                if sr == nil {
                    // nil equals to check pass
                    continue
                }
                // check slot result
                if sr.IsBlocked() {
                    ruleCheckRet = sr
                    break
                }
            }
        }
        if ruleCheckRet == nil {
            ctx.RuleCheckResult.ResetToPass()
        } else {
            ctx.RuleCheckResult = ruleCheckRet
        }

        // execute statistic slot
        ss := sc.stats
        ruleCheckRet = ctx.RuleCheckResult
        if len(ss) > 0 {
            for _, s := range ss {
                // indicate the result of rule based checking slot.
                if !ruleCheckRet.IsBlocked() {
                    s.OnEntryPassed(ctx)
                } else {
                    // The block error should not be nil.
                    s.OnEntryBlocked(ctx, ruleCheckRet.blockErr)
                }
            }
        }
        return ruleCheckRet
    }

    func (sc *SlotChain) exit(ctx *EntryContext) {
        if ctx == nil || ctx.Entry() == nil {
            logging.Error(errors.New("nil EntryContext or SentinelEntry"), "")
            return
        }
        // The OnCompleted is called only when entry passed
        if ctx.IsBlocked() {
            return
        }
        for _, s := range sc.stats {
            s.OnCompleted(ctx)
        }
        // relieve the context here
    }   

   // api/slot_chain.go

    func BuildDefaultSlotChain() *base.SlotChain {
        sc := base.NewSlotChain()
        sc.AddStatPrepareSlotLast(&stat.ResourceNodePrepareSlot{})

        sc.AddRuleCheckSlotLast(&flow.Slot{})

        sc.AddStatSlotLast(&flow.StandaloneStatSlot{})

        return sc
    }

    var globalSlotChain = BuildDefaultSlotChain()

    // api/api.go

    // Entry is the basic API of Sentinel.
    func Entry(resource string, opts ...EntryOption) (*base.SentinelEntry, *base.BlockError) {
        options := entryOptsPool.Get().(*EntryOptions)
        options.slotChain = globalSlotChain

        return entry(resource, options)
    }