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Go Concurrency

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Cloudflare
Cloudflare

This document summarizes key concepts of Go concurrency including goroutines, channels, and synchronization primitives. It discusses how goroutines are lightweight processes that enable creating thousands concurrently with low overhead. Channels provide a way for goroutines to communicate by sending and receiving values. Examples demonstrate using goroutines and channels for signaling, timeouts, and implementing a load balancer to distribute HTTP requests across a pool of workers.

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Go Concurrency March 27, 2013 John Graham-Cumming www.cloudflare.com!
Fundamentals •  goroutines •  Very lightweight processes •  All scheduling handled internally by the Go runtime •  Unless you are CPU bound you do not have to think about scheduling •  Channel-based communication •  The right way for goroutines to talk to each other •  Synchronization Primitives •  For when a channel is too heavyweight •  Not covered in this talk www.cloudflare.com!
goroutines •  “Lightweight” •  Starting 10,000 goroutines on my MacBook Pro took 22ms •  Allocated memory increased by 3,014,000 bytes (301 bytes per goroutine) •  https://gist.github.com/jgrahamc/5253020 •  Not unusual at CloudFlare to have a single Go program running 10,000s of goroutines with 1,000,000s of goroutines created during life program. •  So, go yourFunc() as much as you like. www.cloudflare.com!
Channels •  Quick syntax review c := make(chan bool)– Makes an unbuffered channel of bools c <- x – Sends a value on the channel <- c – Waits to receive a value on the channel x = <- c – Waits to receive a value and stores it in x x, ok = <- c – Waits to receive a value; ok will be false if channel is closed and empty. www.cloudflare.com!
Unbuffered channels are best •  They provide both communication and synchronization func from(connection chan int) {! connection <- rand.Intn(100)! }! ! func to(connection chan int) {! i := <- connection! fmt.Printf("Someone sent me %dn", i)! }! ! func main() {! cpus := runtime.NumCPU()! runtime.GOMAXPROCS(cpus)! ! connection := make(chan int)! go from(connection)! go to(connection)! }! www.cloudflare.com!
Using channels for signaling (1) •  Sometimes just closing a channel is enough c := make(chan bool)! ! go func() {! !// ... do some stuff! !close(c)! }()! ! // ... do some other stuff! <- c! www.cloudflare.com!
Using channels for signaling (2) •  Close a channel to coordinate multiple goroutines func worker(start chan bool) {! <- start! // ... do stuff! }! ! func main() {! start := make(chan bool)! ! for i := 0; i < 100; i++ {! go worker(start)! }! ! close(start)! ! // ... all workers running now! }! www.cloudflare.com!
Select •  Select statement enables sending/receiving on multiple channels at once select {! case x := <- somechan:! // ... do stuff with x! ! case y, ok := <- someOtherchan:! // ... do stuff with y! // check ok to see if someOtherChan! // is closed! ! case outputChan <- z:! // ... ok z was sent! ! default:! // ... no one wants to communicate! }! www.cloudflare.com!
Common idiom: for/select! for {! select {! case x := <- somechan:! // ... do stuff with x! ! case y, ok := <- someOtherchan:! // ... do stuff with y! // check ok to see if someOtherChan! // is closed! ! case outputChan <- z:! // ... ok z was sent! ! default:! // ... no one wants to communicate! }! }! www.cloudflare.com!
Using channels for signaling (4) •  Close a channel to terminate multiple goroutines func worker(die chan bool) {! for {! select {! // ... do stuff cases! case <- die: ! return! }! }! }! ! func main() {! die := make(chan bool)! for i := 0; i < 100; i++ {! go worker(die)! }! close(die)! }! www.cloudflare.com!
Using channels for signaling (5) •  Terminate a goroutine and verify termination func worker(die chan bool) {! for {! select {! // ... do stuff cases! case <- die:! // ... do termination tasks ! die <- true! return! }! }! }! func main() {! die := make(chan bool)! go worker(die)! die <- true! <- die! }! www.cloudflare.com!
Example: unique ID service •  Just receive from id to get a unique ID •  Safe to share id channel across routines id := make(chan string)! ! go func() {! var counter int64 = 0! for {! id <- fmt.Sprintf("%x", counter)! counter += 1! }! }()! ! x := <- id // x will be 1! x = <- id // x will be 2! www.cloudflare.com!
Example: memory recycler func recycler(give, get chan []byte) {! q := new(list.List)! ! for {! if q.Len() == 0 {! q.PushFront(make([]byte, 100))! }! ! e := q.Front()! ! select {! case s := <-give:! q.PushFront(s[:0])! ! case get <- e.Value.([]byte):! q.Remove(e)! }! }! }! www.cloudflare.com!
Timeout func worker(start chan bool) {! for {! !timeout := time.After(30 * time.Second)! !select {! // ... do some stuff! ! case <- timeout:! return! }! func worker(start chan bool) {! }! timeout := time.After(30 * time.Second)! }! for {! !select {! // ... do some stuff! ! case <- timeout:! return! }! }! }! www.cloudflare.com!
Heartbeat func worker(start chan bool) {! heartbeat := time.Tick(30 * time.Second)! for {! !select {! // ... do some stuff! ! case <- heartbeat:! // ... do heartbeat stuff! }! }! }! www.cloudflare.com!
Example: network multiplexor •  Multiple goroutines can send on the same channel func worker(messages chan string) {! for {! var msg string // ... generate a message! messages <- msg! }! }! func main() {! messages := make(chan string)! conn, _ := net.Dial("tcp", "example.com")! ! for i := 0; i < 100; i++ {! go worker(messages)! }! for {! msg := <- messages! conn.Write([]byte(msg))! }! }! www.cloudflare.com!
Example: first of N •  Dispatch requests and get back the first one to complete type response struct {! resp *http.Response! url string! }! ! func get(url string, r chan response ) {! if resp, err := http.Get(url); err == nil {! r <- response{resp, url}! }! }! ! func main() {! first := make(chan response)! for _, url := range []string{"http://code.jquery.com/jquery-1.9.1.min.js",! "http://cdnjs.cloudflare.com/ajax/libs/jquery/1.9.1/jquery.min.js",! "http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js",! "http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.9.1.min.js"} {! go get(url, first)! }! ! r := <- first! // ... do something! }! www.cloudflare.com!
range! •  Can be used to consume all values from a channel func generator(strings chan string) {! strings <- "Five hour's New York jet lag"! strings <- "and Cayce Pollard wakes in Camden Town"! strings <- "to the dire and ever-decreasing circles"! strings <- "of disrupted circadian rhythm."! close(strings)! }! ! func main() {! strings := make(chan string)! go generator(strings)! ! for s := range strings {! fmt.Printf("%s ", s)! }! fmt.Printf("n");! }! www.cloudflare.com!
Passing a ‘response’ channel type work struct {! url string! resp chan *http.Response! }! ! func getter(w chan work) {! for {! do := <- w! resp, _ := http.Get(do.url)! do.resp <- resp! }! }! ! func main() {! w := make(chan work)! ! go getter(w)! ! resp := make(chan *http.Response)! w <- work{"http://cdnjs.cloudflare.com/jquery/1.9.1/jquery.min.js",! resp}! ! r := <- resp! }! www.cloudflare.com!
Buffered channels •  Can be useful to create queues •  But make reasoning about concurrency more difficult c := make(chan bool, 100) ! www.cloudflare.com!
Example: an HTTP load balancer •  Limited number of HTTP clients can make requests for URLs •  Unlimited number of goroutines need to request URLs and get responses •  Solution: an HTTP request load balancer www.cloudflare.com!
A URL getter type job struct {! url string! resp chan *http.Response! }! ! type worker struct {! jobs chan *job! count int! }! ! func (w *worker) getter(done chan *worker) {! for {! j := <- w.jobs! resp, _ := http.Get(j.url)! j.resp <- resp! done <- w! }! }! www.cloudflare.com!
A way to get URLs func get(jobs chan *job, url string, answer chan string) {! resp := make(chan *http.Response)! jobs <- &job{url, resp}! r := <- resp! answer <- r.Request.URL.String()! }! ! func main() {! jobs := balancer(10, 10)! answer := make(chan string)! for {! var url string! if _, err := fmt.Scanln(&url); err != nil {! break! }! go get(jobs, url, answer)! }! for u := range answer {! fmt.Printf("%sn", u)! }! }! www.cloudflare.com!
A load balancer func balancer(count int, depth int) chan *job {! jobs := make(chan *job)! done := make(chan *worker)! workers := make([]*worker, count)! ! for i := 0; i < count; i++ {! workers[i] = &worker{make(chan *job,
 depth), 0}! go workers[i].getter(done)! }! ! ! select {! go func() {! case j := <- jobsource:! for {! free.jobs <- j! var free *worker! free.count++! min := depth! ! for _, w := range workers {! case w := <- done:! if w.count < min {! w.count—! free = w! }! min = w.count! }! }! }()! }! ! ! return jobs! var jobsource chan *job! }! if free != nil {! jobsource = jobs! }! www.cloudflare.com!
Top 500 web sites loaded www.cloudflare.com!
THANKS The Go Way: “small sequential pieces joined by channels” www.cloudflare.com!

More Related Content

Go Concurrency

  • 1. Go Concurrency March 27, 2013 John Graham-Cumming www.cloudflare.com!
  • 2. Fundamentals •  goroutines •  Very lightweight processes •  All scheduling handled internally by the Go runtime •  Unless you are CPU bound you do not have to think about scheduling •  Channel-based communication •  The right way for goroutines to talk to each other •  Synchronization Primitives •  For when a channel is too heavyweight •  Not covered in this talk www.cloudflare.com!
  • 3. goroutines •  “Lightweight” •  Starting 10,000 goroutines on my MacBook Pro took 22ms •  Allocated memory increased by 3,014,000 bytes (301 bytes per goroutine) •  https://gist.github.com/jgrahamc/5253020 •  Not unusual at CloudFlare to have a single Go program running 10,000s of goroutines with 1,000,000s of goroutines created during life program. •  So, go yourFunc() as much as you like. www.cloudflare.com!
  • 4. Channels •  Quick syntax review c := make(chan bool)– Makes an unbuffered channel of bools c <- x – Sends a value on the channel <- c – Waits to receive a value on the channel x = <- c – Waits to receive a value and stores it in x x, ok = <- c – Waits to receive a value; ok will be false if channel is closed and empty. www.cloudflare.com!
  • 5. Unbuffered channels are best •  They provide both communication and synchronization func from(connection chan int) {! connection <- rand.Intn(100)! }! ! func to(connection chan int) {! i := <- connection! fmt.Printf("Someone sent me %dn", i)! }! ! func main() {! cpus := runtime.NumCPU()! runtime.GOMAXPROCS(cpus)! ! connection := make(chan int)! go from(connection)! go to(connection)! }! www.cloudflare.com!
  • 6. Using channels for signaling (1) •  Sometimes just closing a channel is enough c := make(chan bool)! ! go func() {! !// ... do some stuff! !close(c)! }()! ! // ... do some other stuff! <- c! www.cloudflare.com!
  • 7. Using channels for signaling (2) •  Close a channel to coordinate multiple goroutines func worker(start chan bool) {! <- start! // ... do stuff! }! ! func main() {! start := make(chan bool)! ! for i := 0; i < 100; i++ {! go worker(start)! }! ! close(start)! ! // ... all workers running now! }! www.cloudflare.com!
  • 8. Select •  Select statement enables sending/receiving on multiple channels at once select {! case x := <- somechan:! // ... do stuff with x! ! case y, ok := <- someOtherchan:! // ... do stuff with y! // check ok to see if someOtherChan! // is closed! ! case outputChan <- z:! // ... ok z was sent! ! default:! // ... no one wants to communicate! }! www.cloudflare.com!
  • 9. Common idiom: for/select! for {! select {! case x := <- somechan:! // ... do stuff with x! ! case y, ok := <- someOtherchan:! // ... do stuff with y! // check ok to see if someOtherChan! // is closed! ! case outputChan <- z:! // ... ok z was sent! ! default:! // ... no one wants to communicate! }! }! www.cloudflare.com!
  • 10. Using channels for signaling (4) •  Close a channel to terminate multiple goroutines func worker(die chan bool) {! for {! select {! // ... do stuff cases! case <- die: ! return! }! }! }! ! func main() {! die := make(chan bool)! for i := 0; i < 100; i++ {! go worker(die)! }! close(die)! }! www.cloudflare.com!
  • 11. Using channels for signaling (5) •  Terminate a goroutine and verify termination func worker(die chan bool) {! for {! select {! // ... do stuff cases! case <- die:! // ... do termination tasks ! die <- true! return! }! }! }! func main() {! die := make(chan bool)! go worker(die)! die <- true! <- die! }! www.cloudflare.com!
  • 12. Example: unique ID service •  Just receive from id to get a unique ID •  Safe to share id channel across routines id := make(chan string)! ! go func() {! var counter int64 = 0! for {! id <- fmt.Sprintf("%x", counter)! counter += 1! }! }()! ! x := <- id // x will be 1! x = <- id // x will be 2! www.cloudflare.com!
  • 13. Example: memory recycler func recycler(give, get chan []byte) {! q := new(list.List)! ! for {! if q.Len() == 0 {! q.PushFront(make([]byte, 100))! }! ! e := q.Front()! ! select {! case s := <-give:! q.PushFront(s[:0])! ! case get <- e.Value.([]byte):! q.Remove(e)! }! }! }! www.cloudflare.com!
  • 14. Timeout func worker(start chan bool) {! for {! !timeout := time.After(30 * time.Second)! !select {! // ... do some stuff! ! case <- timeout:! return! }! func worker(start chan bool) {! }! timeout := time.After(30 * time.Second)! }! for {! !select {! // ... do some stuff! ! case <- timeout:! return! }! }! }! www.cloudflare.com!
  • 15. Heartbeat func worker(start chan bool) {! heartbeat := time.Tick(30 * time.Second)! for {! !select {! // ... do some stuff! ! case <- heartbeat:! // ... do heartbeat stuff! }! }! }! www.cloudflare.com!
  • 16. Example: network multiplexor •  Multiple goroutines can send on the same channel func worker(messages chan string) {! for {! var msg string // ... generate a message! messages <- msg! }! }! func main() {! messages := make(chan string)! conn, _ := net.Dial("tcp", "example.com")! ! for i := 0; i < 100; i++ {! go worker(messages)! }! for {! msg := <- messages! conn.Write([]byte(msg))! }! }! www.cloudflare.com!
  • 17. Example: first of N •  Dispatch requests and get back the first one to complete type response struct {! resp *http.Response! url string! }! ! func get(url string, r chan response ) {! if resp, err := http.Get(url); err == nil {! r <- response{resp, url}! }! }! ! func main() {! first := make(chan response)! for _, url := range []string{"http://code.jquery.com/jquery-1.9.1.min.js",! "http://cdnjs.cloudflare.com/ajax/libs/jquery/1.9.1/jquery.min.js",! "http://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js",! "http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.9.1.min.js"} {! go get(url, first)! }! ! r := <- first! // ... do something! }! www.cloudflare.com!
  • 18. range! •  Can be used to consume all values from a channel func generator(strings chan string) {! strings <- "Five hour's New York jet lag"! strings <- "and Cayce Pollard wakes in Camden Town"! strings <- "to the dire and ever-decreasing circles"! strings <- "of disrupted circadian rhythm."! close(strings)! }! ! func main() {! strings := make(chan string)! go generator(strings)! ! for s := range strings {! fmt.Printf("%s ", s)! }! fmt.Printf("n");! }! www.cloudflare.com!
  • 19. Passing a ‘response’ channel type work struct {! url string! resp chan *http.Response! }! ! func getter(w chan work) {! for {! do := <- w! resp, _ := http.Get(do.url)! do.resp <- resp! }! }! ! func main() {! w := make(chan work)! ! go getter(w)! ! resp := make(chan *http.Response)! w <- work{"http://cdnjs.cloudflare.com/jquery/1.9.1/jquery.min.js",! resp}! ! r := <- resp! }! www.cloudflare.com!
  • 20. Buffered channels •  Can be useful to create queues •  But make reasoning about concurrency more difficult c := make(chan bool, 100) ! www.cloudflare.com!
  • 21. Example: an HTTP load balancer •  Limited number of HTTP clients can make requests for URLs •  Unlimited number of goroutines need to request URLs and get responses •  Solution: an HTTP request load balancer www.cloudflare.com!
  • 22. A URL getter type job struct {! url string! resp chan *http.Response! }! ! type worker struct {! jobs chan *job! count int! }! ! func (w *worker) getter(done chan *worker) {! for {! j := <- w.jobs! resp, _ := http.Get(j.url)! j.resp <- resp! done <- w! }! }! www.cloudflare.com!
  • 23. A way to get URLs func get(jobs chan *job, url string, answer chan string) {! resp := make(chan *http.Response)! jobs <- &job{url, resp}! r := <- resp! answer <- r.Request.URL.String()! }! ! func main() {! jobs := balancer(10, 10)! answer := make(chan string)! for {! var url string! if _, err := fmt.Scanln(&url); err != nil {! break! }! go get(jobs, url, answer)! }! for u := range answer {! fmt.Printf("%sn", u)! }! }! www.cloudflare.com!
  • 24. A load balancer func balancer(count int, depth int) chan *job {! jobs := make(chan *job)! done := make(chan *worker)! workers := make([]*worker, count)! ! for i := 0; i < count; i++ {! workers[i] = &worker{make(chan *job,
 depth), 0}! go workers[i].getter(done)! }! ! ! select {! go func() {! case j := <- jobsource:! for {! free.jobs <- j! var free *worker! free.count++! min := depth! ! for _, w := range workers {! case w := <- done:! if w.count < min {! w.count—! free = w! }! min = w.count! }! }! }()! }! ! ! return jobs! var jobsource chan *job! }! if free != nil {! jobsource = jobs! }! www.cloudflare.com!
  • 25. Top 500 web sites loaded www.cloudflare.com!
  • 26. THANKS The Go Way: “small sequential pieces joined by channels” www.cloudflare.com!