89 lines
2.4 KiB
Go
89 lines
2.4 KiB
Go
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// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package util
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import "time"
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// A Throttle permits throttling of a goroutine by
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// calling the Throttle method repeatedly.
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//
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type Throttle struct {
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f float64 // f = (1-r)/r for 0 < r < 1
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dt time.Duration // minimum run time slice; >= 0
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tr time.Duration // accumulated time running
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ts time.Duration // accumulated time stopped
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tt time.Time // earliest throttle time (= time Throttle returned + tm)
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}
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// NewThrottle creates a new Throttle with a throttle value r and
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// a minimum allocated run time slice of dt:
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//
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// r == 0: "empty" throttle; the goroutine is always sleeping
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// r == 1: full throttle; the goroutine is never sleeping
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//
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// A value of r == 0.6 throttles a goroutine such that it runs
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// approx. 60% of the time, and sleeps approx. 40% of the time.
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// Values of r < 0 or r > 1 are clamped down to values between 0 and 1.
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// Values of dt < 0 are set to 0.
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//
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func NewThrottle(r float64, dt time.Duration) *Throttle {
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var f float64
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switch {
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case r <= 0:
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f = -1 // indicates always sleep
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case r >= 1:
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f = 0 // assume r == 1 (never sleep)
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default:
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// 0 < r < 1
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f = (1 - r) / r
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}
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if dt < 0 {
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dt = 0
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}
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return &Throttle{f: f, dt: dt, tt: time.Now().Add(dt)}
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}
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// Throttle calls time.Sleep such that over time the ratio tr/ts between
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// accumulated run (tr) and sleep times (ts) approximates the value 1/(1-r)
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// where r is the throttle value. Throttle returns immediately (w/o sleeping)
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// if less than tm ns have passed since the last call to Throttle.
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//
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func (p *Throttle) Throttle() {
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if p.f < 0 {
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select {} // always sleep
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}
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t0 := time.Now()
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if t0.Before(p.tt) {
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return // keep running (minimum time slice not exhausted yet)
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}
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// accumulate running time
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p.tr += t0.Sub(p.tt) + p.dt
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// compute sleep time
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// Over time we want:
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//
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// tr/ts = r/(1-r)
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//
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// Thus:
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//
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// ts = tr*f with f = (1-r)/r
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//
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// After some incremental run time δr added to the total run time
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// tr, the incremental sleep-time δs to get to the same ratio again
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// after waking up from time.Sleep is:
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if δs := time.Duration(float64(p.tr)*p.f) - p.ts; δs > 0 {
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time.Sleep(δs)
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}
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// accumulate (actual) sleep time
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t1 := time.Now()
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p.ts += t1.Sub(t0)
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// set earliest next throttle time
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p.tt = t1.Add(p.dt)
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}
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