slowshepherd.go

package main

import (
	"fmt"
	"time"
)

// SlowShepherd is for making sure that a func used in a tight loop
// does not cause a thundering herd problem. If the function
// thunderingHerdFunc returns quicker than the sleepInterval given,
// SlowShepherd will take exactly the sleepInterval given to return. If
// the thunderingHerdFunc takes longer than the sleepInterval given,
// SlowShepherd will return in whatever time the function took to
// complete but no more time than that. (Also, remember that
// sleepInterval is in nanoseconds.)
func SlowShepherd(sleepInterval int64, thunderingHerdFunc func()) {
	sleeper := make(chan int)
	go func() {
		thunderingHerdFunc()
		sleeper <- 1
	}()
	time.Sleep(sleepInterval)
	<-sleeper
}

func main() {
	// Some functions to test the sleepiness of the shepherd
	f := func() {
		time.Sleep(250000000) // quarter of a second
	}
	g := func() {
		time.Sleep(5000000000) // five seconds
	}
	fs := []func(){f, g}
	intv := int64(2000000000) // two seconds

	// this would be a better example if it was an infinite loop
	for x, fun := range (fs) {
		t1 := time.UTC().Seconds()
		SlowShepherd(intv, fun)
		t2 := time.UTC().Seconds()
		fmt.Printf("%v Took %v seconds.\n", x, t2-t1)
	}
}