diff options
Diffstat (limited to 'vendor/github.com/rcrowley/go-metrics/ewma.go')
-rw-r--r-- | vendor/github.com/rcrowley/go-metrics/ewma.go | 118 |
1 files changed, 118 insertions, 0 deletions
diff --git a/vendor/github.com/rcrowley/go-metrics/ewma.go b/vendor/github.com/rcrowley/go-metrics/ewma.go new file mode 100644 index 000000000..694a1d033 --- /dev/null +++ b/vendor/github.com/rcrowley/go-metrics/ewma.go @@ -0,0 +1,118 @@ +package metrics + +import ( + "math" + "sync" + "sync/atomic" +) + +// EWMAs continuously calculate an exponentially-weighted moving average +// based on an outside source of clock ticks. +type EWMA interface { + Rate() float64 + Snapshot() EWMA + Tick() + Update(int64) +} + +// NewEWMA constructs a new EWMA with the given alpha. +func NewEWMA(alpha float64) EWMA { + if UseNilMetrics { + return NilEWMA{} + } + return &StandardEWMA{alpha: alpha} +} + +// NewEWMA1 constructs a new EWMA for a one-minute moving average. +func NewEWMA1() EWMA { + return NewEWMA(1 - math.Exp(-5.0/60.0/1)) +} + +// NewEWMA5 constructs a new EWMA for a five-minute moving average. +func NewEWMA5() EWMA { + return NewEWMA(1 - math.Exp(-5.0/60.0/5)) +} + +// NewEWMA15 constructs a new EWMA for a fifteen-minute moving average. +func NewEWMA15() EWMA { + return NewEWMA(1 - math.Exp(-5.0/60.0/15)) +} + +// EWMASnapshot is a read-only copy of another EWMA. +type EWMASnapshot float64 + +// Rate returns the rate of events per second at the time the snapshot was +// taken. +func (a EWMASnapshot) Rate() float64 { return float64(a) } + +// Snapshot returns the snapshot. +func (a EWMASnapshot) Snapshot() EWMA { return a } + +// Tick panics. +func (EWMASnapshot) Tick() { + panic("Tick called on an EWMASnapshot") +} + +// Update panics. +func (EWMASnapshot) Update(int64) { + panic("Update called on an EWMASnapshot") +} + +// NilEWMA is a no-op EWMA. +type NilEWMA struct{} + +// Rate is a no-op. +func (NilEWMA) Rate() float64 { return 0.0 } + +// Snapshot is a no-op. +func (NilEWMA) Snapshot() EWMA { return NilEWMA{} } + +// Tick is a no-op. +func (NilEWMA) Tick() {} + +// Update is a no-op. +func (NilEWMA) Update(n int64) {} + +// StandardEWMA is the standard implementation of an EWMA and tracks the number +// of uncounted events and processes them on each tick. It uses the +// sync/atomic package to manage uncounted events. +type StandardEWMA struct { + uncounted int64 // /!\ this should be the first member to ensure 64-bit alignment + alpha float64 + rate float64 + init bool + mutex sync.Mutex +} + +// Rate returns the moving average rate of events per second. +func (a *StandardEWMA) Rate() float64 { + a.mutex.Lock() + defer a.mutex.Unlock() + return a.rate * float64(1e9) +} + +// Snapshot returns a read-only copy of the EWMA. +func (a *StandardEWMA) Snapshot() EWMA { + return EWMASnapshot(a.Rate()) +} + +// Tick ticks the clock to update the moving average. It assumes it is called +// every five seconds. +func (a *StandardEWMA) Tick() { + count := atomic.LoadInt64(&a.uncounted) + atomic.AddInt64(&a.uncounted, -count) + instantRate := float64(count) / float64(5e9) + a.mutex.Lock() + defer a.mutex.Unlock() + if a.init { + a.rate += a.alpha * (instantRate - a.rate) + } else { + a.init = true + a.rate = instantRate + } +} + +// Update adds n uncounted events. +func (a *StandardEWMA) Update(n int64) { + atomic.AddInt64(&a.uncounted, n) +} |