You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
275 lines
8.1 KiB
275 lines
8.1 KiB
//
|
|
// Written by Maxim Khitrov (November 2012)
|
|
//
|
|
|
|
// Package flowrate provides the tools for monitoring and limiting the flow rate
|
|
// of an arbitrary data stream.
|
|
package flowrate
|
|
|
|
import (
|
|
"math"
|
|
"sync"
|
|
"time"
|
|
)
|
|
|
|
// Monitor monitors and limits the transfer rate of a data stream.
|
|
type Monitor struct {
|
|
mu sync.Mutex // Mutex guarding access to all internal fields
|
|
active bool // Flag indicating an active transfer
|
|
start time.Duration // Transfer start time (clock() value)
|
|
bytes int64 // Total number of bytes transferred
|
|
samples int64 // Total number of samples taken
|
|
|
|
rSample float64 // Most recent transfer rate sample (bytes per second)
|
|
rEMA float64 // Exponential moving average of rSample
|
|
rPeak float64 // Peak transfer rate (max of all rSamples)
|
|
rWindow float64 // rEMA window (seconds)
|
|
|
|
sBytes int64 // Number of bytes transferred since sLast
|
|
sLast time.Duration // Most recent sample time (stop time when inactive)
|
|
sRate time.Duration // Sampling rate
|
|
|
|
tBytes int64 // Number of bytes expected in the current transfer
|
|
tLast time.Duration // Time of the most recent transfer of at least 1 byte
|
|
}
|
|
|
|
// New creates a new flow control monitor. Instantaneous transfer rate is
|
|
// measured and updated for each sampleRate interval. windowSize determines the
|
|
// weight of each sample in the exponential moving average (EMA) calculation.
|
|
// The exact formulas are:
|
|
//
|
|
// sampleTime = currentTime - prevSampleTime
|
|
// sampleRate = byteCount / sampleTime
|
|
// weight = 1 - exp(-sampleTime/windowSize)
|
|
// newRate = weight*sampleRate + (1-weight)*oldRate
|
|
//
|
|
// The default values for sampleRate and windowSize (if <= 0) are 100ms and 1s,
|
|
// respectively.
|
|
func New(sampleRate, windowSize time.Duration) *Monitor {
|
|
if sampleRate = clockRound(sampleRate); sampleRate <= 0 {
|
|
sampleRate = 5 * clockRate
|
|
}
|
|
if windowSize <= 0 {
|
|
windowSize = 1 * time.Second
|
|
}
|
|
now := clock()
|
|
return &Monitor{
|
|
active: true,
|
|
start: now,
|
|
rWindow: windowSize.Seconds(),
|
|
sLast: now,
|
|
sRate: sampleRate,
|
|
tLast: now,
|
|
}
|
|
}
|
|
|
|
// Update records the transfer of n bytes and returns n. It should be called
|
|
// after each Read/Write operation, even if n is 0.
|
|
func (m *Monitor) Update(n int) int {
|
|
m.mu.Lock()
|
|
m.update(n)
|
|
m.mu.Unlock()
|
|
return n
|
|
}
|
|
|
|
// Hack to set the current rEMA.
|
|
func (m *Monitor) SetREMA(rEMA float64) {
|
|
m.mu.Lock()
|
|
m.rEMA = rEMA
|
|
m.samples++
|
|
m.mu.Unlock()
|
|
}
|
|
|
|
// IO is a convenience method intended to wrap io.Reader and io.Writer method
|
|
// execution. It calls m.Update(n) and then returns (n, err) unmodified.
|
|
func (m *Monitor) IO(n int, err error) (int, error) {
|
|
return m.Update(n), err
|
|
}
|
|
|
|
// Done marks the transfer as finished and prevents any further updates or
|
|
// limiting. Instantaneous and current transfer rates drop to 0. Update, IO, and
|
|
// Limit methods become NOOPs. It returns the total number of bytes transferred.
|
|
func (m *Monitor) Done() int64 {
|
|
m.mu.Lock()
|
|
if now := m.update(0); m.sBytes > 0 {
|
|
m.reset(now)
|
|
}
|
|
m.active = false
|
|
m.tLast = 0
|
|
n := m.bytes
|
|
m.mu.Unlock()
|
|
return n
|
|
}
|
|
|
|
// timeRemLimit is the maximum Status.TimeRem value.
|
|
const timeRemLimit = 999*time.Hour + 59*time.Minute + 59*time.Second
|
|
|
|
// Status represents the current Monitor status. All transfer rates are in bytes
|
|
// per second rounded to the nearest byte.
|
|
type Status struct {
|
|
Active bool // Flag indicating an active transfer
|
|
Start time.Time // Transfer start time
|
|
Duration time.Duration // Time period covered by the statistics
|
|
Idle time.Duration // Time since the last transfer of at least 1 byte
|
|
Bytes int64 // Total number of bytes transferred
|
|
Samples int64 // Total number of samples taken
|
|
InstRate int64 // Instantaneous transfer rate
|
|
CurRate int64 // Current transfer rate (EMA of InstRate)
|
|
AvgRate int64 // Average transfer rate (Bytes / Duration)
|
|
PeakRate int64 // Maximum instantaneous transfer rate
|
|
BytesRem int64 // Number of bytes remaining in the transfer
|
|
TimeRem time.Duration // Estimated time to completion
|
|
Progress Percent // Overall transfer progress
|
|
}
|
|
|
|
// Status returns current transfer status information. The returned value
|
|
// becomes static after a call to Done.
|
|
func (m *Monitor) Status() Status {
|
|
m.mu.Lock()
|
|
now := m.update(0)
|
|
s := Status{
|
|
Active: m.active,
|
|
Start: clockToTime(m.start),
|
|
Duration: m.sLast - m.start,
|
|
Idle: now - m.tLast,
|
|
Bytes: m.bytes,
|
|
Samples: m.samples,
|
|
PeakRate: round(m.rPeak),
|
|
BytesRem: m.tBytes - m.bytes,
|
|
Progress: percentOf(float64(m.bytes), float64(m.tBytes)),
|
|
}
|
|
if s.BytesRem < 0 {
|
|
s.BytesRem = 0
|
|
}
|
|
if s.Duration > 0 {
|
|
rAvg := float64(s.Bytes) / s.Duration.Seconds()
|
|
s.AvgRate = round(rAvg)
|
|
if s.Active {
|
|
s.InstRate = round(m.rSample)
|
|
s.CurRate = round(m.rEMA)
|
|
if s.BytesRem > 0 {
|
|
if tRate := 0.8*m.rEMA + 0.2*rAvg; tRate > 0 {
|
|
ns := float64(s.BytesRem) / tRate * 1e9
|
|
if ns > float64(timeRemLimit) {
|
|
ns = float64(timeRemLimit)
|
|
}
|
|
s.TimeRem = clockRound(time.Duration(ns))
|
|
}
|
|
}
|
|
}
|
|
}
|
|
m.mu.Unlock()
|
|
return s
|
|
}
|
|
|
|
// Limit restricts the instantaneous (per-sample) data flow to rate bytes per
|
|
// second. It returns the maximum number of bytes (0 <= n <= want) that may be
|
|
// transferred immediately without exceeding the limit. If block == true, the
|
|
// call blocks until n > 0. want is returned unmodified if want < 1, rate < 1,
|
|
// or the transfer is inactive (after a call to Done).
|
|
//
|
|
// At least one byte is always allowed to be transferred in any given sampling
|
|
// period. Thus, if the sampling rate is 100ms, the lowest achievable flow rate
|
|
// is 10 bytes per second.
|
|
//
|
|
// For usage examples, see the implementation of Reader and Writer in io.go.
|
|
func (m *Monitor) Limit(want int, rate int64, block bool) (n int) {
|
|
if want < 1 || rate < 1 {
|
|
return want
|
|
}
|
|
m.mu.Lock()
|
|
|
|
// Determine the maximum number of bytes that can be sent in one sample
|
|
limit := round(float64(rate) * m.sRate.Seconds())
|
|
if limit <= 0 {
|
|
limit = 1
|
|
}
|
|
|
|
// If block == true, wait until m.sBytes < limit
|
|
if now := m.update(0); block {
|
|
for m.sBytes >= limit && m.active {
|
|
now = m.waitNextSample(now)
|
|
}
|
|
}
|
|
|
|
// Make limit <= want (unlimited if the transfer is no longer active)
|
|
if limit -= m.sBytes; limit > int64(want) || !m.active {
|
|
limit = int64(want)
|
|
}
|
|
m.mu.Unlock()
|
|
|
|
if limit < 0 {
|
|
limit = 0
|
|
}
|
|
return int(limit)
|
|
}
|
|
|
|
// SetTransferSize specifies the total size of the data transfer, which allows
|
|
// the Monitor to calculate the overall progress and time to completion.
|
|
func (m *Monitor) SetTransferSize(bytes int64) {
|
|
if bytes < 0 {
|
|
bytes = 0
|
|
}
|
|
m.mu.Lock()
|
|
m.tBytes = bytes
|
|
m.mu.Unlock()
|
|
}
|
|
|
|
// update accumulates the transferred byte count for the current sample until
|
|
// clock() - m.sLast >= m.sRate. The monitor status is updated once the current
|
|
// sample is done.
|
|
func (m *Monitor) update(n int) (now time.Duration) {
|
|
if !m.active {
|
|
return
|
|
}
|
|
if now = clock(); n > 0 {
|
|
m.tLast = now
|
|
}
|
|
m.sBytes += int64(n)
|
|
if sTime := now - m.sLast; sTime >= m.sRate {
|
|
t := sTime.Seconds()
|
|
if m.rSample = float64(m.sBytes) / t; m.rSample > m.rPeak {
|
|
m.rPeak = m.rSample
|
|
}
|
|
|
|
// Exponential moving average using a method similar to *nix load
|
|
// average calculation. Longer sampling periods carry greater weight.
|
|
if m.samples > 0 {
|
|
w := math.Exp(-t / m.rWindow)
|
|
m.rEMA = m.rSample + w*(m.rEMA-m.rSample)
|
|
} else {
|
|
m.rEMA = m.rSample
|
|
}
|
|
m.reset(now)
|
|
}
|
|
return
|
|
}
|
|
|
|
// reset clears the current sample state in preparation for the next sample.
|
|
func (m *Monitor) reset(sampleTime time.Duration) {
|
|
m.bytes += m.sBytes
|
|
m.samples++
|
|
m.sBytes = 0
|
|
m.sLast = sampleTime
|
|
}
|
|
|
|
// waitNextSample sleeps for the remainder of the current sample. The lock is
|
|
// released and reacquired during the actual sleep period, so it's possible for
|
|
// the transfer to be inactive when this method returns.
|
|
func (m *Monitor) waitNextSample(now time.Duration) time.Duration {
|
|
const minWait = 5 * time.Millisecond
|
|
current := m.sLast
|
|
|
|
// sleep until the last sample time changes (ideally, just one iteration)
|
|
for m.sLast == current && m.active {
|
|
d := current + m.sRate - now
|
|
m.mu.Unlock()
|
|
if d < minWait {
|
|
d = minWait
|
|
}
|
|
time.Sleep(d)
|
|
m.mu.Lock()
|
|
now = m.update(0)
|
|
}
|
|
return now
|
|
}
|