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// Copyright 2010 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 main
import (
"container/heap"
"flag"
"fmt"
"math/rand"
"time"
)
const nRequester = 100
const nWorker = 10
var roundRobin = flag.Bool("r", false, "use round-robin scheduling")
// Simulation of some work: just sleep for a while and report how long.
func op() int {
n := rand.Int63n(1e9)
time.Sleep(nWorker * n)
return int(n)
}
type Request struct {
fn func() int
c chan int
}
func requester(work chan Request) {
c := make(chan int)
for {
time.Sleep(rand.Int63n(nWorker * 2e9))
work <- Request{op, c}
<-c
}
}
type Worker struct {
i int
requests chan Request
pending int
}
func (w *Worker) work(done chan *Worker) {
for {
req := <-w.requests
req.c <- req.fn()
done <- w
}
}
type Pool []*Worker
func (p Pool) Len() int { return len(p) }
func (p Pool) Less(i, j int) bool {
return p[i].pending < p[j].pending
}
func (p *Pool) Swap(i, j int) {
a := *p
a[i], a[j] = a[j], a[i]
a[i].i = i
a[j].i = j
}
func (p *Pool) Push(x interface{}) {
a := *p
n := len(a)
a = a[0 : n+1]
w := x.(*Worker)
a[n] = w
w.i = n
*p = a
}
func (p *Pool) Pop() interface{} {
a := *p
*p = a[0 : len(a)-1]
w := a[len(a)-1]
w.i = -1 // for safety
return w
}
type Balancer struct {
pool Pool
done chan *Worker
i int
}
func NewBalancer() *Balancer {
done := make(chan *Worker, nWorker)
b := &Balancer{make(Pool, 0, nWorker), done, 0}
for i := 0; i < nWorker; i++ {
w := &Worker{requests: make(chan Request, nRequester)}
heap.Push(&b.pool, w)
go w.work(b.done)
}
return b
}
func (b *Balancer) balance(work chan Request) {
for {
select {
case req := <-work:
b.dispatch(req)
case w := <-b.done:
b.completed(w)
}
b.print()
}
}
func (b *Balancer) print() {
sum := 0
sumsq := 0
for _, w := range b.pool {
fmt.Printf("%d ", w.pending)
sum += w.pending
sumsq += w.pending * w.pending
}
avg := float64(sum) / float64(len(b.pool))
variance := float64(sumsq)/float64(len(b.pool)) - avg*avg
fmt.Printf(" %.2f %.2f\n", avg, variance)
}
func (b *Balancer) dispatch(req Request) {
if *roundRobin {
w := b.pool[b.i]
w.requests <- req
w.pending++
b.i++
if b.i >= len(b.pool) {
b.i = 0
}
return
}
w := heap.Pop(&b.pool).(*Worker)
w.requests <- req
w.pending++
// fmt.Printf("started %p; now %d\n", w, w.pending)
heap.Push(&b.pool, w)
}
func (b *Balancer) completed(w *Worker) {
if *roundRobin {
w.pending--
return
}
w.pending--
// fmt.Printf("finished %p; now %d\n", w, w.pending)
heap.Remove(&b.pool, w.i)
heap.Push(&b.pool, w)
}
func main() {
flag.Parse()
work := make(chan Request)
for i := 0; i < nRequester; i++ {
go requester(work)
}
NewBalancer().balance(work)
}
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