mirror of
https://github.com/golang/go
synced 2024-11-18 16:24:42 -07:00
89 lines
2.4 KiB
Go
89 lines
2.4 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style
|
|
// license that can be found in the LICENSE file.
|
|
|
|
package util
|
|
|
|
import "time"
|
|
|
|
// A Throttle permits throttling of a goroutine by
|
|
// calling the Throttle method repeatedly.
|
|
//
|
|
type Throttle struct {
|
|
f float64 // f = (1-r)/r for 0 < r < 1
|
|
dt time.Duration // minimum run time slice; >= 0
|
|
tr time.Duration // accumulated time running
|
|
ts time.Duration // accumulated time stopped
|
|
tt time.Time // earliest throttle time (= time Throttle returned + tm)
|
|
}
|
|
|
|
// NewThrottle creates a new Throttle with a throttle value r and
|
|
// a minimum allocated run time slice of dt:
|
|
//
|
|
// r == 0: "empty" throttle; the goroutine is always sleeping
|
|
// r == 1: full throttle; the goroutine is never sleeping
|
|
//
|
|
// A value of r == 0.6 throttles a goroutine such that it runs
|
|
// approx. 60% of the time, and sleeps approx. 40% of the time.
|
|
// Values of r < 0 or r > 1 are clamped down to values between 0 and 1.
|
|
// Values of dt < 0 are set to 0.
|
|
//
|
|
func NewThrottle(r float64, dt time.Duration) *Throttle {
|
|
var f float64
|
|
switch {
|
|
case r <= 0:
|
|
f = -1 // indicates always sleep
|
|
case r >= 1:
|
|
f = 0 // assume r == 1 (never sleep)
|
|
default:
|
|
// 0 < r < 1
|
|
f = (1 - r) / r
|
|
}
|
|
if dt < 0 {
|
|
dt = 0
|
|
}
|
|
return &Throttle{f: f, dt: dt, tt: time.Now().Add(dt)}
|
|
}
|
|
|
|
// Throttle calls time.Sleep such that over time the ratio tr/ts between
|
|
// accumulated run (tr) and sleep times (ts) approximates the value 1/(1-r)
|
|
// where r is the throttle value. Throttle returns immediately (w/o sleeping)
|
|
// if less than tm ns have passed since the last call to Throttle.
|
|
//
|
|
func (p *Throttle) Throttle() {
|
|
if p.f < 0 {
|
|
select {} // always sleep
|
|
}
|
|
|
|
t0 := time.Now()
|
|
if t0.Before(p.tt) {
|
|
return // keep running (minimum time slice not exhausted yet)
|
|
}
|
|
|
|
// accumulate running time
|
|
p.tr += t0.Sub(p.tt) + p.dt
|
|
|
|
// compute sleep time
|
|
// Over time we want:
|
|
//
|
|
// tr/ts = r/(1-r)
|
|
//
|
|
// Thus:
|
|
//
|
|
// ts = tr*f with f = (1-r)/r
|
|
//
|
|
// After some incremental run time δr added to the total run time
|
|
// tr, the incremental sleep-time δs to get to the same ratio again
|
|
// after waking up from time.Sleep is:
|
|
if δs := time.Duration(float64(p.tr)*p.f) - p.ts; δs > 0 {
|
|
time.Sleep(δs)
|
|
}
|
|
|
|
// accumulate (actual) sleep time
|
|
t1 := time.Now()
|
|
p.ts += t1.Sub(t0)
|
|
|
|
// set earliest next throttle time
|
|
p.tt = t1.Add(p.dt)
|
|
}
|