1 files changed, 168 insertions, 0 deletions
diff --git a/doc/talks/io2010/balance.go b/doc/talks/io2010/balance.go
new file mode 100644
index 000000000..b01f7468c
--- /dev/null
+++ b/doc/talks/io2010/balance.go
@@ -0,0 +1,168 @@
+// 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"
+	"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)
+}