VOL-2496 Add "event listen" command to voltctl
Change-Id: I8f1fb34b55f56c8125142ac289e2f19fc170d804
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 0000000..a8183dd
--- /dev/null
+++ b/vendor/github.com/rcrowley/go-metrics/ewma.go
@@ -0,0 +1,138 @@
+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 uint64
+ init uint32
+ mutex sync.Mutex
+}
+
+// Rate returns the moving average rate of events per second.
+func (a *StandardEWMA) Rate() float64 {
+ currentRate := math.Float64frombits(atomic.LoadUint64(&a.rate)) * float64(1e9)
+ return currentRate
+}
+
+// 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() {
+ // Optimization to avoid mutex locking in the hot-path.
+ if atomic.LoadUint32(&a.init) == 1 {
+ a.updateRate(a.fetchInstantRate())
+ } else {
+ // Slow-path: this is only needed on the first Tick() and preserves transactional updating
+ // of init and rate in the else block. The first conditional is needed below because
+ // a different thread could have set a.init = 1 between the time of the first atomic load and when
+ // the lock was acquired.
+ a.mutex.Lock()
+ if atomic.LoadUint32(&a.init) == 1 {
+ // The fetchInstantRate() uses atomic loading, which is unecessary in this critical section
+ // but again, this section is only invoked on the first successful Tick() operation.
+ a.updateRate(a.fetchInstantRate())
+ } else {
+ atomic.StoreUint32(&a.init, 1)
+ atomic.StoreUint64(&a.rate, math.Float64bits(a.fetchInstantRate()))
+ }
+ a.mutex.Unlock()
+ }
+}
+
+func (a *StandardEWMA) fetchInstantRate() float64 {
+ count := atomic.LoadInt64(&a.uncounted)
+ atomic.AddInt64(&a.uncounted, -count)
+ instantRate := float64(count) / float64(5e9)
+ return instantRate
+}
+
+func (a *StandardEWMA) updateRate(instantRate float64) {
+ currentRate := math.Float64frombits(atomic.LoadUint64(&a.rate))
+ currentRate += a.alpha * (instantRate - currentRate)
+ atomic.StoreUint64(&a.rate, math.Float64bits(currentRate))
+}
+
+// Update adds n uncounted events.
+func (a *StandardEWMA) Update(n int64) {
+ atomic.AddInt64(&a.uncounted, n)
+}