moira

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package metrics
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import (
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	"sync"
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	"github.com/rcrowley/go-metrics"
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)
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const (
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	movingWindowSize = 1028
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)
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// movingWindowSample is sample using moving window reservoir to keep selection of stream values.
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type movingWindowSample struct {
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	buffer      []int64
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	count       int64
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	index, size int
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	overflow    bool
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	lock        sync.RWMutex
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}
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func newMovingWindowSample() metrics.Sample {
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	if metrics.UseNilMetrics {
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		return metrics.NilSample{}
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	}
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	return &movingWindowSample{
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		buffer: make([]int64, movingWindowSize),
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		size:   movingWindowSize,
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	}
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}
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// Clear clears all sample
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func (mw *movingWindowSample) Clear() {
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	mw.lock.Lock()
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	defer mw.lock.Unlock()
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	mw.count = 0
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	mw.index = 0
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	mw.overflow = false
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}
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// Count returns the number of samples recorded, which may exceed the reservoir size.
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func (mw *movingWindowSample) Count() int64 {
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	mw.lock.RLock()
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	defer mw.lock.RUnlock()
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	return mw.count
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}
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// Max returns the maximum value in the sample.
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func (mw *movingWindowSample) Max() int64 {
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	return metrics.SampleMax(mw.Values())
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}
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// Mean returns the mean of the values in the sample.
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func (mw *movingWindowSample) Mean() float64 {
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	return metrics.SampleMean(mw.Values())
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}
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// Min returns the minimum value in the sample
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func (mw *movingWindowSample) Min() int64 {
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	return metrics.SampleMin(mw.Values())
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}
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// Percentile returns an arbitrary percentile of values in the sample.
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func (mw *movingWindowSample) Percentile(p float64) float64 {
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	return metrics.SamplePercentile(mw.Values(), p)
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}
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// Percentiles returns a slice of arbitrary percentiles of values in the sample.
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func (mw *movingWindowSample) Percentiles(ps []float64) []float64 {
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	return metrics.SamplePercentiles(mw.Values(), ps)
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}
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// Size returns the size of the sample, which is at most the reservoir size.
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func (mw *movingWindowSample) Size() int {
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	mw.lock.RLock()
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	defer mw.lock.RUnlock()
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	if mw.overflow {
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		return mw.size
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	} else {
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		return mw.index
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	}
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}
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// Snapshot returns a read-only copy of the sample.
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func (mw *movingWindowSample) Snapshot() metrics.Sample {
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	mw.lock.RLock()
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	defer mw.lock.RUnlock()
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	return metrics.NewSampleSnapshot(mw.count, mw.Values())
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}
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// StdDev returns the standard deviation of the values in the sample.
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func (mw *movingWindowSample) StdDev() float64 {
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	return metrics.SampleStdDev(mw.Values())
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}
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// Sum returns the sum of the values in the sample.
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func (mw *movingWindowSample) Sum() int64 {
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	return metrics.SampleSum(mw.Values())
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}
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// Update samples a new value.
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func (mw *movingWindowSample) Update(v int64) {
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	mw.lock.Lock()
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	defer mw.lock.Unlock()
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	mw.buffer[mw.index] = v
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	mw.count++
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	mw.index++
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	if mw.index == mw.size {
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		mw.index = 0
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		mw.overflow = true
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	}
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}
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// Values returns a copy of the values in the sample.
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func (mw *movingWindowSample) Values() []int64 {
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	mw.lock.RLock()
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	defer mw.lock.RUnlock()
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	values := make([]int64, mw.size)
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	if mw.overflow {
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		// buffer has been overflow, so window's values consist of 2 parts:
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		// from current position (included) to the end of buffer and from the beginning of buffer to current position (excluded)
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		// e.g.: [7, 8, 3, 4, 5, 6], current position = 3, values are [3, 4, 5, 6, 7, 8]
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		copied := copy(values, mw.buffer[mw.index:])
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		if copied < mw.size {
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			copy(values[copied:], mw.buffer[:mw.index])
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		}
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	} else {
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		// buffer hasn't been overflown, so window's values is slice from beginning of buffer to current position (latter is excluded)
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		// e.g.: [1, 2, 3, 4, 0, 0], current position = 4, values are [1, 2, 3, 4, 0, 0]
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		copy(values, mw.buffer[0:mw.index])
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	}
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	return values
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}
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// Variance returns the variance of the values in the sample.
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func (mw *movingWindowSample) Variance() float64 {
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	return metrics.SampleVariance(mw.Values())
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}
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