flowrate

Documentation

Overview

Package flowrate provides the tools for monitoring and limiting the flow rate of an arbitrary data stream.

Index

• Variables
• func TimeNow() time.Time
• type Monitor
  • func New(startAt time.Time, sampleRate, windowSize time.Duration) *Monitor
  • func (m *Monitor) CurrentTransferRate() int64
  • func (m *Monitor) Done() int64
  • func (m *Monitor) IO(n int, err error) (int, error)
  • func (m *Monitor) Limit(want int, rate int64, block bool) (n int)
  • func (m *Monitor) SetREMA(rEMA float64)
  • func (m *Monitor) SetTransferSize(bytes int64)
  • func (m *Monitor) Status() Status
  • func (m *Monitor) Update(n int) int
• type Percent
  • func (p Percent) Float() float64
  • func (p Percent) String() string
• type Status

Variables

var Now = TimeNow

Functions

func TimeNow

func TimeNow() time.Time

Types

type Monitor

type Monitor struct {
	// contains filtered or unexported fields
}

Monitor monitors and limits the transfer rate of a data stream.

func New

func New(startAt time.Time, sampleRate, windowSize time.Duration) *Monitor

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 (*Monitor) CurrentTransferRate

func (m *Monitor) CurrentTransferRate() int64

CurrentTransferRate returns the current transfer rate

func (*Monitor) Done

func (m *Monitor) Done() int64

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 (*Monitor) IO

func (m *Monitor) IO(n int, err error) (int, error)

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 (*Monitor) Limit

func (m *Monitor) Limit(want int, rate int64, block bool) (n int)

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 (*Monitor) SetREMA

func (m *Monitor) SetREMA(rEMA float64)

Hack to set the current rEMA.

func (*Monitor) SetTransferSize

func (m *Monitor) SetTransferSize(bytes int64)

SetTransferSize specifies the total size of the data transfer, which allows the Monitor to calculate the overall progress and time to completion.

func (*Monitor) Status

func (m *Monitor) Status() Status

Status returns current transfer status information. The returned value becomes static after a call to Done.

func (*Monitor) Update

func (m *Monitor) Update(n int) int

Update records the transfer of n bytes and returns n. It should be called after each Read/Write operation, even if n is 0.

type Percent

type Percent uint32

Percent represents a percentage in increments of 1/1000th of a percent.

func (Percent) Float

func (p Percent) Float() float64

func (Percent) String

func (p Percent) String() string

type Status

type Status struct {
	Start    time.Time     // Transfer start time
	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
	Duration time.Duration // Time period covered by the statistics
	Idle     time.Duration // Time since the last transfer of at least 1 byte
	TimeRem  time.Duration // Estimated time to completion
	Progress Percent       // Overall transfer progress
	Active   bool          // Flag indicating an active transfer
}

Status represents the current Monitor status. All transfer rates are in bytes per second rounded to the nearest byte.