#17 Enable use of MQTT broker as a library -> passing a logger reference to the broker instance

* add pool

* elastic workerpool

* del buf

* modify usage

* modify readme

README.md

@@ -16,43 +16,26 @@ $ go run main.go
 
 ## Usage of hmq:
 ~~~
-Usage of ./hmq:
+Usage: hmq [options]
-  -w int
+
-        worker num to process message, perfer (client num)/10. (default 1024)
+Broker Options:
-  -worker int
+    -w,  --worker <number>            Worker num to process message, perfer (client num)/10. (default 1024)
-        worker num to process message, perfer (client num)/10. (default 1024)
+    -p,  --port <port>                Use port for clients (default: 1883)
-  -h string
+         --host <host>                Network host to listen on. (default "0.0.0.0")
-        Network host to listen on. (default "0.0.0.0")
+    -ws, --wsport <port>              Use port for websocket monitoring
-  -host string
+    -wsp,--wspath <path>              Use path for websocket monitoring
-        Network host to listen on. (default "0.0.0.0")
+    -c,  --config <file>              Configuration file
-  -p string
+
-        Port to listen on. (default "1883")
+Logging Options:
-  -port string
+    -d, --debug <bool>                Enable debugging output (default false)
-        Port to listen on. (default "1883")
+    -D                                Debug enabled
-  -c string
+
-        config file for hmq
+Cluster Options:
-  -config string
+    -r,  --router  <rurl>             Router who maintenance cluster info
-        config file for hmq
+    -cp, --clusterport <cluster-port> Cluster listen port for others
-  -cluster string
+
-        Cluster ip from which members can connect.
+Common Options:
-  -cluster_listen string
+    -h, --help                        Show this message
-        Cluster ip from which members can connect.
-  -cluster_port string
-        Cluster port from which members can connect.
-  -cp string
-        Cluster port from which members can connect.
-  -r string
-        Router who maintenance cluster info
-  -router string
-        Router who maintenance cluster info
-  -ws_path string
-        path for ws to listen on
-  -ws_port string
-        port for ws to listen on
-  -wspath string
-        path for ws to listen on
-  -wsport string
-        port for ws to listen on
 ~~~
 
 ### hmq.config
@@ -105,6 +88,9 @@ Usage of ./hmq:
 ### Cluster
 ```bash
  1, start router for hmq  (https://github.com/fhmq/router.git)
+ 	$ go get github.com/fhmq/router
+ 	$ cd $GOPATH/github.com/fhmq/router
+ 	$ go run main.go
  2, config router in hmq.config  ("router": "127.0.0.1:9888")
  
 ```

broker/auth.go

@@ -6,6 +6,7 @@ import (
 	"strings"
 
 	"github.com/fhmq/hmq/lib/acl"
+
 	"go.uber.org/zap"
 
 	"github.com/fsnotify/fsnotify"

broker/broker.go

@@ -18,14 +18,18 @@ import (
 	"go.uber.org/zap"
 
 	"golang.org/x/net/websocket"
-
-	"github.com/fhmq/hmq/logger"
 )
 
 var (
-	log = logger.Get().Named("Broker")
+	log                  *zap.Logger
+	messagePoolQueueSize = 4096
 )
 
+type Message struct {
+	client *client
+	packet packets.ControlPacket
+}
+
 type Broker struct {
 	id         string
 	cid        uint64
@@ -33,6 +37,7 @@ type Broker struct {
 	config     *Config
 	tlsConfig  *tls.Config
 	AclConfig  *acl.ACLConfig
+	dispatcher *Dispatcher
 	clients    sync.Map
 	routes     sync.Map
 	remotes    sync.Map
@@ -42,10 +47,12 @@ type Broker struct {
 	queues     map[string]int
 }
 
-func NewBroker(config *Config) (*Broker, error) {
+func NewBroker(config *Config, logger *zap.Logger) (*Broker, error) {
+	log = logger
 	b := &Broker{
 		id:         GenUniqueId(),
 		config:     config,
+		dispatcher: NewDispatcher(),
 		sl:         NewSublist(),
 		rl:         NewRetainList(),
 		nodes:      make(map[string]interface{}),
@@ -71,12 +78,16 @@ func NewBroker(config *Config) (*Broker, error) {
 	return b, nil
 }
 
+func (b *Broker) DispatchMessage(msg *Message) {
+	b.dispatcher.Dispatch(msg)
+
+}
+
 func (b *Broker) Start() {
 	if b == nil {
 		log.Error("broker is null")
 		return
 	}
-	StartDispatcher()
 
 	//listen clinet over tcp
 	if b.config.Port != "" {
@@ -124,7 +135,7 @@ func StateMonitor() {
 func (b *Broker) StartWebsocketListening() {
 	path := b.config.WsPath
 	hp := ":" + b.config.WsPort
-	log.Info("Start Websocket Listening on ", zap.String("hp", hp), zap.String("path", path))
+	log.Info("Start Websocket Listener on:", zap.String("hp", hp), zap.String("path", path))
 	http.Handle(path, websocket.Handler(b.wsHandler))
 	var err error
 	if b.config.WsTLS {
@@ -303,34 +314,27 @@ func (b *Broker) handleConnection(typ int, conn net.Conn, idx uint64) {
 
 	cid := c.info.clientID
 
-	var msgPool *MessagePool
 	var exist bool
 	var old interface{}
 
 	switch typ {
 	case CLIENT:
-		msgPool = MSGPool[idx%MessagePoolNum].GetPool()
-		c.mp = msgPool
 		old, exist = b.clients.Load(cid)
 		if exist {
 			log.Warn("client exist, close old...", zap.String("clientID", c.info.clientID))
 			ol, ok := old.(*client)
 			if ok {
-				msg := &Message{client: c, packet: DisconnectdPacket}
+				ol.Close()
-				ol.mp.queue <- msg
 			}
 		}
 		b.clients.Store(cid, c)
 	case ROUTER:
-		msgPool = MSGPool[(MessagePoolNum + idx)].GetPool()
-		c.mp = msgPool
 		old, exist = b.routes.Load(cid)
 		if exist {
 			log.Warn("router exist, close old...")
 			ol, ok := old.(*client)
 			if ok {
-				msg := &Message{client: c, packet: DisconnectdPacket}
+				ol.Close()
-				ol.mp.queue <- msg
 			}
 		}
 		b.routes.Store(cid, c)
@@ -383,7 +387,6 @@ func (b *Broker) ConnectToDiscovery() {
 	c.SendConnect()
 	c.SendInfo()
 
-	c.mp = &MSGPool[(MessagePoolNum + 2)]
 	go c.readLoop()
 	go c.StartPing()
 }
@@ -446,10 +449,7 @@ func (b *Broker) connectRouter(id, addr string) {
 	c.init()
 	b.remotes.Store(cid, c)
 
-	c.mp = MSGPool[(MessagePoolNum + 1)].GetPool()
-
 	c.SendConnect()
-	// c.SendInfo()
 
 	go c.readLoop()
 	go c.StartPing()

broker/client.go

@@ -4,6 +4,7 @@ package broker
 
 import (
 	"net"
+	"reflect"
 	"strings"
 	"sync"
 	"time"
@@ -38,7 +39,6 @@ type client struct {
 	status int
 	closed chan int
 	smu    sync.RWMutex
-	mp     *MessagePool
 	subs   map[string]*subscription
 	rsubs  map[string]*subInfo
 }
@@ -90,7 +90,6 @@ func (c *client) keepAlive(ch chan int) {
 	defer close(ch)
 	keepalive := time.Duration(c.info.keepalive*3/2) * time.Second
 	timer := time.NewTimer(keepalive)
-	msgPool := c.mp
 
 	for {
 		select {
@@ -102,8 +101,7 @@ func (c *client) keepAlive(ch chan int) {
 				continue
 			}
 			log.Error("Client exceeded timeout, disconnecting. ", zap.String("ClientID", c.info.clientID), zap.Uint16("keepalive", c.info.keepalive))
-			msg := &Message{client: c, packet: DisconnectdPacket}
+			c.broker.DispatchMessage(&Message{client: c, packet: DisconnectdPacket})
-			msgPool.queue <- msg
 			timer.Stop()
 			return
 		case _, ok := <-c.closed:
@@ -116,8 +114,7 @@ func (c *client) keepAlive(ch chan int) {
 
 func (c *client) readLoop() {
 	nc := c.conn
-	msgPool := c.mp
+	if nc == nil {
-	if nc == nil || msgPool == nil {
 		return
 	}
 
@@ -130,18 +127,16 @@ func (c *client) readLoop() {
 			log.Error("read packet error: ", zap.Error(err), zap.String("ClientID", c.info.clientID))
 			break
 		}
-
+		// keepalive channel
 		ch <- 1
 
-		msg := &Message{
+		c.broker.DispatchMessage(&Message{
 			client: c,
 			packet: packet,
+		})
 	}
-		msgPool.queue <- msg
+
-	}
+	c.broker.DispatchMessage(&Message{client: c, packet: DisconnectdPacket})
-	msg := &Message{client: c, packet: DisconnectdPacket}
-	msgPool.queue <- msg
-	msgPool.Reduce()
 }
 
 func ProcessMessage(msg *Message) {
@@ -150,10 +145,10 @@ func ProcessMessage(msg *Message) {
 	if ca == nil {
 		return
 	}
-	log.Debug("Recv message from client,", zap.String("ClientID", c.info.clientID))
+
+	log.Debug("Recv message:", zap.String("message type", reflect.TypeOf(msg.packet).String()[9:]), zap.String("ClientID", c.info.clientID))
 	switch ca.(type) {
 	case *packets.ConnackPacket:
-
 	case *packets.ConnectPacket:
 	case *packets.PublishPacket:
 		packet := ca.(*packets.PublishPacket)

broker/config.go

@@ -10,7 +10,9 @@ import (
 	"flag"
 	"fmt"
 	"io/ioutil"
+	"os"
 
+	"github.com/fhmq/hmq/logger"
 	"go.uber.org/zap"
 )
 
@@ -28,6 +30,7 @@ type Config struct {
 	TlsInfo TLSInfo   `json:"tlsInfo"`
 	Acl     bool      `json:"acl"`
 	AclConf string    `json:"aclConf"`
+	Debug   bool      `json:"-"`
 }
 
 type RouteInfo struct {
@@ -49,30 +52,60 @@ var DefaultConfig *Config = &Config{
 	Acl:    false,
 }
 
-func ConfigureConfig() (*Config, error) {
+func showHelp() {
+	fmt.Printf("%s\n", usageStr)
+	os.Exit(0)
+}
+
+func ConfigureConfig(args []string) (*Config, error) {
 	config := &Config{}
 	var (
+		help       bool
 		configFile string
 	)
-	flag.IntVar(&config.Worker, "w", 1024, "worker num to process message, perfer (client num)/10.")
+	fs := flag.NewFlagSet("hmq-broker", flag.ExitOnError)
-	flag.IntVar(&config.Worker, "worker", 1024, "worker num to process message, perfer (client num)/10.")
+	fs.Usage = showHelp
-	flag.StringVar(&config.Port, "port", "1883", "Port to listen on.")
+
-	flag.StringVar(&config.Port, "p", "1883", "Port to listen on.")
+	fs.BoolVar(&help, "h", false, "Show this message.")
-	flag.StringVar(&config.Host, "host", "0.0.0.0", "Network host to listen on.")
+	fs.BoolVar(&help, "help", false, "Show this message.")
-	flag.StringVar(&config.Host, "h", "0.0.0.0", "Network host to listen on.")
+	fs.IntVar(&config.Worker, "w", 1024, "worker num to process message, perfer (client num)/10.")
-	flag.StringVar(&config.Cluster.Host, "cluster", "", "Cluster ip from which members can connect.")
+	fs.IntVar(&config.Worker, "worker", 1024, "worker num to process message, perfer (client num)/10.")
-	flag.StringVar(&config.Cluster.Host, "cluster_listen", "", "Cluster ip from which members can connect.")
+	fs.StringVar(&config.Port, "port", "1883", "Port to listen on.")
-	flag.StringVar(&config.Cluster.Port, "cp", "", "Cluster port from which members can connect.")
+	fs.StringVar(&config.Port, "p", "1883", "Port to listen on.")
-	flag.StringVar(&config.Cluster.Port, "cluster_port", "", "Cluster port from which members can connect.")
+	fs.StringVar(&config.Host, "host", "0.0.0.0", "Network host to listen on")
-	flag.StringVar(&config.Router, "r", "", "Router who maintenance cluster info")
+	fs.StringVar(&config.Cluster.Port, "cp", "", "Cluster port from which members can connect.")
-	flag.StringVar(&config.Router, "router", "", "Router who maintenance cluster info")
+	fs.StringVar(&config.Cluster.Port, "clusterport", "", "Cluster port from which members can connect.")
-	flag.StringVar(&config.WsPort, "wsport", "", "port for ws to listen on")
+	fs.StringVar(&config.Router, "r", "", "Router who maintenance cluster info")
-	flag.StringVar(&config.WsPort, "ws_port", "", "port for ws to listen on")
+	fs.StringVar(&config.Router, "router", "", "Router who maintenance cluster info")
-	flag.StringVar(&config.WsPath, "wspath", "", "path for ws to listen on")
+	fs.StringVar(&config.WsPort, "ws", "", "port for ws to listen on")
-	flag.StringVar(&config.WsPath, "ws_path", "", "path for ws to listen on")
+	fs.StringVar(&config.WsPort, "wsport", "", "port for ws to listen on")
-	flag.StringVar(&configFile, "config", "", "config file for hmq")
+	fs.StringVar(&config.WsPath, "wsp", "", "path for ws to listen on")
-	flag.StringVar(&configFile, "c", "", "config file for hmq")
+	fs.StringVar(&config.WsPath, "wspath", "", "path for ws to listen on")
-	flag.Parse()
+	fs.StringVar(&configFile, "config", "", "config file for hmq")
+	fs.StringVar(&configFile, "c", "", "config file for hmq")
+	fs.BoolVar(&config.Debug, "debug", false, "enable Debug logging.")
+	fs.BoolVar(&config.Debug, "d", false, "enable Debug logging.")
+
+	fs.Bool("D", true, "enable Debug logging.")
+
+	if err := fs.Parse(args); err != nil {
+		return nil, err
+	}
+
+	if help {
+		showHelp()
+		return nil, nil
+	}
+
+	fs.Visit(func(f *flag.Flag) {
+		switch f.Name {
+		case "D":
+			config.Debug = true
+		}
+	})
+
+	logger.InitLogger(config.Debug)
+	log = logger.Get().Named("Broker")
 
 	if configFile != "" {
 		tmpConfig, e := LoadConfig(configFile)
@@ -116,8 +149,6 @@ func (config *Config) check() error {
 		config.Worker = 1024
 	}
 
-	WorkNum = config.Worker
-
 	if config.Port != "" {
 		if config.Host == "" {
 			config.Host = "0.0.0.0"

broker/dispatcher.go

@@ -1,46 +1,25 @@
-/* Copyright (c) 2018, joy.zhou <chowyu08@gmail.com>
- */
 package broker
 
-var WorkNum int
+import (
+	"sync"
+)
 
+// Dispatcher will delegate ProcessMessage func to multiple goroutines
 type Dispatcher struct {
-	WorkerPool chan chan *Message
+	workerPool *sync.Pool
-}
-
-func StartDispatcher() {
-	InitMessagePool()
-	dispatcher := NewDispatcher()
-	dispatcher.Run()
-}
-
-func (d *Dispatcher) Run() {
-	// starting n number of workers
-	for i := 0; i < WorkNum; i++ {
-		worker := NewWorker(d.WorkerPool)
-		worker.Start()
-	}
-	go d.dispatch()
 }
 
+// NewDispatcher create a *Dispatcher instance
 func NewDispatcher() *Dispatcher {
-	pool := make(chan chan *Message, WorkNum)
+	return &Dispatcher{workerPool: &sync.Pool{
-	return &Dispatcher{WorkerPool: pool}
+		New: func() interface{} {
-}
+			return NewWorker()
-
+		},
-func (d *Dispatcher) dispatch() {
+	},
-	for i := 0; i < (MessagePoolNum + 3); i++ {
+	}
-		go func(idx int) {
-			for {
-				select {
-				case msg := <-MSGPool[idx].queue:
-					go func(msg *Message) {
-						msgChannel := <-d.WorkerPool
-						msgChannel <- msg
-					}(msg)
-				}
-			}
-		}(i)
 }
 
+// Dispatch a message to the workers
+func (d *Dispatcher) Dispatch(message *Message) {
+	d.workerPool.Get().(Worker).WorkerChannel <- Work{WorkerPool: d.workerPool, Message: message}
 }

broker/msgpool.go

@@ -1,64 +0,0 @@
-/* Copyright (c) 2018, joy.zhou <chowyu08@gmail.com>
- */
-package broker
-
-import (
-	"sync"
-
-	"github.com/eclipse/paho.mqtt.golang/packets"
-)
-
-const (
-	MaxUser               = 1024 * 1024
-	MessagePoolNum        = 1024
-	MessagePoolUser       = MaxUser / MessagePoolNum
-	MessagePoolMessageNum = MaxUser / MessagePoolNum * 4
-)
-
-type Message struct {
-	client *client
-	packet packets.ControlPacket
-}
-
-var (
-	MSGPool []MessagePool
-)
-
-type MessagePool struct {
-	l       sync.Mutex
-	maxuser int
-	user    int
-	queue   chan *Message
-}
-
-func InitMessagePool() {
-	MSGPool = make([]MessagePool, (MessagePoolNum + 3))
-	for i := 0; i < (MessagePoolNum + 3); i++ {
-		MSGPool[i].Init(MessagePoolUser, MessagePoolMessageNum)
-	}
-}
-
-func (p *MessagePool) Init(num int, maxusernum int) {
-	p.maxuser = maxusernum
-	p.queue = make(chan *Message, num)
-}
-
-func (p *MessagePool) GetPool() *MessagePool {
-	p.l.Lock()
-	if p.user+1 < p.maxuser {
-		p.user += 1
-		p.l.Unlock()
-		return p
-	} else {
-		p.l.Unlock()
-		return nil
-	}
-
-}
-
-func (p *MessagePool) Reduce() {
-	p.l.Lock()
-	p.user -= 1
-	p.l.Unlock()
-
-}

broker/usage.go

@@ -0,0 +1,24 @@
+package broker
+
+var usageStr = `
+Usage: hmq [options]
+
+Broker Options:
+    -w,  --worker <number>            Worker num to process message, perfer (client num)/10. (default 1024)
+    -p,  --port <port>                Use port for clients (default: 1883)
+         --host <host>                Network host to listen on. (default "0.0.0.0")
+    -ws, --wsport <port>              Use port for websocket monitoring
+    -wsp,--wspath <path>              Use path for websocket monitoring
+    -c,  --config <file>              Configuration file
+
+Logging Options:
+    -d, --debug <bool>                Enable debugging output (default false)
+    -D                                Debug and trace
+
+Cluster Options:
+    -r,  --router  <rurl>             Router who maintenance cluster info
+    -cp, --clusterport <cluster-port> Cluster listen port for others
+
+Common Options:
+    -h, --help                        Show this message
+`

broker/worker.go

@@ -1,39 +1,28 @@
-/* Copyright (c) 2018, joy.zhou <chowyu08@gmail.com>
- */
 package broker
 
+import "sync"
+
+type Work struct {
+	WorkerPool *sync.Pool
+	Message    *Message
+}
+
 type Worker struct {
-	WorkerPool chan chan *Message
+	WorkerChannel chan Work
-	MsgChannel chan *Message
-	quit       chan bool
 }
 
-func NewWorker(workerPool chan chan *Message) Worker {
+func NewWorker() Worker {
-	return Worker{
+	w := Worker{WorkerChannel: make(chan Work)}
-		WorkerPool: workerPool,
+	return w.Start()
-		MsgChannel: make(chan *Message),
-		quit:       make(chan bool)}
 }
 
-func (w Worker) Start() {
+func (w Worker) Start() Worker {
 	go func() {
-		for {
+		for work := range w.WorkerChannel {
-			// register the current worker into the worker queue.
+			ProcessMessage(work.Message)
-			w.WorkerPool <- w.MsgChannel
+			// put the worker back
-			select {
+			work.WorkerPool.Put(w)
-			case msg := <-w.MsgChannel:
-				// we have received a work request.
-				ProcessMessage(msg)
-			case <-w.quit:
-				return
-			}
 		}
 	}()
-}
+	return w
-
-// Stop signals the worker to stop listening for work requests.
-func (w Worker) Stop() {
-	go func() {
-		w.quit <- true
-	}()
 }

logger/logger.go

@@ -8,44 +8,40 @@ import (
 )
 
 var (
-	// env can be setup at build time with Go Linker. Value could be prod or whatever else for dev env
+	logInstance *zap.Logger
-	env      string
-	instance *zap.Logger
-	logCfg   zap.Config
 )
 
-// NewDevLogger return a logger for dev builds
+// InitDevLogger instanciate a logger for dev builds
-func NewDevLogger() (*zap.Logger, error) {
+func InitDevLogger() {
 	logCfg := zap.NewDevelopmentConfig()
-	return logCfg.Build()
+	logInstance, _ = logCfg.Build()
 }
 
-// NewProdLogger return a logger for production builds
+// InitProdLogger instanciate a logger for production builds
-func NewProdLogger() (*zap.Logger, error) {
+func InitProdLogger() {
 	logCfg := zap.NewProductionConfig()
 	logCfg.DisableStacktrace = true
 	logCfg.Level = zap.NewAtomicLevelAt(zap.InfoLevel)
-	return logCfg.Build()
+	logInstance, _ = logCfg.Build()
 }
 
-func init() {
+func InitLogger(debug bool) {
 	var err error
-	var log *zap.Logger
+	if debug {
-	if env == "prod" {
+		InitDevLogger()
-		log, err = NewProdLogger()
 	} else {
-		log, err = NewDevLogger()
+		InitProdLogger()
 	}
 	if err != nil {
 		panic("Unable to create a logger.")
 	}
-	defer log.Sync()
+	logInstance.Debug("Logger initialization succeeded")
-
-	log.Debug("Logger initialization succeeded")
-	instance = log.Named("hmq")
 }
 
-// Get return a *zap.Logger instance
+// Get the existing *zap.Logger instance. If none have been created, it'll instanciate de dev logger
 func Get() *zap.Logger {
-	return instance
+	if logInstance == nil {
+		InitDevLogger()
+	}
+	return logInstance
 }

logger/logger_test.go

@@ -19,15 +19,11 @@ func TestGet(t *testing.T) {
 }
 
 func TestNewDevLogger(t *testing.T) {
-	logger, err := NewDevLogger()
+	InitDevLogger()
-
+	assert.True(t, Get().Core().Enabled(zap.DebugLevel))
-	assert.Nil(t, err)
-	assert.True(t, logger.Core().Enabled(zap.DebugLevel))
 }
 
 func TestNewProdLogger(t *testing.T) {
-	logger, err := NewProdLogger()
+	InitProdLogger()
-
+	assert.False(t, Get().Core().Enabled(zap.DebugLevel))
-	assert.Nil(t, err)
-	assert.False(t, logger.Core().Enabled(zap.DebugLevel))
 }

main.go

@@ -7,36 +7,32 @@ copyright notice and this permission notice appear in all copies.
 package main
 
 import (
+	"fmt"
 	"os"
 	"os/signal"
 	"runtime"
 
 	"github.com/fhmq/hmq/broker"
 	"github.com/fhmq/hmq/logger"
-	"go.uber.org/zap"
-)
-
-var (
-	log = logger.Get().Named("Main")
 )
 
 func main() {
 	runtime.GOMAXPROCS(runtime.NumCPU())
-	config, err := broker.ConfigureConfig()
+	config, err := broker.ConfigureConfig(os.Args[1:])
 	if err != nil {
-		log.Error("configure broker config error: ", zap.Error(err))
+		fmt.Println("configure broker config error: ", err)
 		return
 	}
-
+	logger.InitLogger(config.Debug)
-	b, err := broker.NewBroker(config)
+	b, err := broker.NewBroker(config, logger.Get())
 	if err != nil {
-		log.Error("New Broker error: ", zap.Error(err))
+		fmt.Println("New Broker error: ", err)
 		return
 	}
 	b.Start()
 
 	s := waitForSignal()
-	log.Info("signal received, broker closed.", zap.Any("signal", s))
+	fmt.Println("signal received, broker closed.", s)
 }
 
 func waitForSignal() os.Signal {

pool/pool.go

@@ -0,0 +1,166 @@
+package pool
+
+import "time"
+
+const (
+	// This value is the size of the queue that workers register their
+	// availability to the dispatcher.  There may be hundreds of workers, but
+	// only a small channel is needed to register some of the workers.
+	readyQueueSize = 16
+
+	// If worker pool receives no new work for this period of time, then stop
+	// a worker goroutine.
+	idleTimeoutSec = 5
+)
+
+type WorkerPool struct {
+	maxWorkers   int
+	timeout      time.Duration
+	taskQueue    chan func()
+	readyWorkers chan chan func()
+	stoppedChan  chan struct{}
+}
+
+func New(maxWorkers int) *WorkerPool {
+	// There must be at least one worker.
+	if maxWorkers < 1 {
+		maxWorkers = 1
+	}
+
+	// taskQueue is unbuffered since items are always removed immediately.
+	pool := &WorkerPool{
+		taskQueue:    make(chan func()),
+		maxWorkers:   maxWorkers,
+		readyWorkers: make(chan chan func(), readyQueueSize),
+		timeout:      time.Second * idleTimeoutSec,
+		stoppedChan:  make(chan struct{}),
+	}
+
+	// Start the task dispatcher.
+	go pool.dispatch()
+
+	return pool
+}
+
+func (p *WorkerPool) Stop() {
+	if p.Stopped() {
+		return
+	}
+	close(p.taskQueue)
+	<-p.stoppedChan
+}
+
+func (p *WorkerPool) Stopped() bool {
+	select {
+	case <-p.stoppedChan:
+		return true
+	default:
+	}
+	return false
+}
+
+func (p *WorkerPool) Submit(task func()) {
+	if task != nil {
+		p.taskQueue <- task
+	}
+}
+
+func (p *WorkerPool) SubmitWait(task func()) {
+	if task == nil {
+		return
+	}
+	doneChan := make(chan struct{})
+	p.taskQueue <- func() {
+		task()
+		close(doneChan)
+	}
+	<-doneChan
+}
+
+func (p *WorkerPool) dispatch() {
+	defer close(p.stoppedChan)
+	timeout := time.NewTimer(p.timeout)
+	var workerCount int
+	var task func()
+	var ok bool
+	var workerTaskChan chan func()
+	startReady := make(chan chan func())
+Loop:
+	for {
+		timeout.Reset(p.timeout)
+		select {
+		case task, ok = <-p.taskQueue:
+			if !ok {
+				break Loop
+			}
+			// Got a task to do.
+			select {
+			case workerTaskChan = <-p.readyWorkers:
+				// A worker is ready, so give task to worker.
+				workerTaskChan <- task
+			default:
+				// No workers ready.
+				// Create a new worker, if not at max.
+				if workerCount < p.maxWorkers {
+					workerCount++
+					go func(t func()) {
+						startWorker(startReady, p.readyWorkers)
+						// Submit the task when the new worker.
+						taskChan := <-startReady
+						taskChan <- t
+					}(task)
+				} else {
+					// Start a goroutine to submit the task when an existing
+					// worker is ready.
+					go func(t func()) {
+						taskChan := <-p.readyWorkers
+						taskChan <- t
+					}(task)
+				}
+			}
+		case <-timeout.C:
+			// Timed out waiting for work to arrive.  Kill a ready worker.
+			if workerCount > 0 {
+				select {
+				case workerTaskChan = <-p.readyWorkers:
+					// A worker is ready, so kill.
+					close(workerTaskChan)
+					workerCount--
+				default:
+					// No work, but no ready workers.  All workers are busy.
+				}
+			}
+		}
+	}
+
+	// Stop all remaining workers as they become ready.
+	for workerCount > 0 {
+		workerTaskChan = <-p.readyWorkers
+		close(workerTaskChan)
+		workerCount--
+	}
+}
+
+func startWorker(startReady, readyWorkers chan chan func()) {
+	go func() {
+		taskChan := make(chan func())
+		var task func()
+		var ok bool
+		// Register availability on starReady channel.
+		startReady <- taskChan
+		for {
+			// Read task from dispatcher.
+			task, ok = <-taskChan
+			if !ok {
+				// Dispatcher has told worker to stop.
+				break
+			}
+
+			// Execute the task.
+			task()
+
+			// Register availability on readyWorkers channel.
+			readyWorkers <- taskChan
+		}
+	}()
+}