Go Concurrency Basics
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The document discusses Go's concurrency features including goroutines, channels, and synchronization tools. It explains that goroutines are lightweight threads managed by Go, and channels provide a means of communication between goroutines. The document also covers potential concurrency issues like deadlocks and provides best practices to avoid anti-patterns when using goroutines and channels.
Go Concurrency Basics
- 1. Go Concurrency Basics Goroutines, channels and standard library By Vitalii Perehonchuk, Software Developer
- 2. www.eliftech.com Go provides Concurrent execution Synchronization and messaging Multi-way concurrent control
- 3. www.eliftech.com Go does NOT provide direct thread manipulation Go multithreading is fully managed by Go runtime. In Go you use goroutines in place of threads
- 4. www.eliftech.com Go provides a race detector Ran with “-race” flag. It watches for unsynchronized access to shared variables.
- 5. www.eliftech.com Goroutine ▪ A lightweight “thread” of execution managed by Go runtime. ▪ A function ran independently in the same address space as other goroutines. ▪ It’s routine to create thousands of goroutines. ▪ Go web servers usually process each request in a separate goroutine.
- 6. www.eliftech.com Goroutine func sidekick() { // Will be never executed. fmt.Println("Sidekick arrived") } func main() { go sidekick() fmt.Println("Hero arrived") }
- 7. www.eliftech.com Goroutine func sidekick() { // Will be executed this time. fmt.Println("Sidekick arrived") } func main() { go sidekick() runtime.Gosched() fmt.Println("Hero arrived") }
- 8. www.eliftech.com Goroutine anti-pattern Do not create functions whose only purpose is to run a goroutine.
- 9. www.eliftech.com Channel Imagine it as a pipe <- <- for communication of goroutines
- 10. www.eliftech.com Channel Imagine it as a pipe for communication of goroutines
- 11. www.eliftech.com Channel A goroutine can wait for a value from a channel
- 12. www.eliftech.com Channel A goroutine can wait for a value from a channel func main() { myChan := make(chan int) <- myChan // deadlock fmt.Println("Hi everyone") }
- 13. www.eliftech.com Channel A goroutine can wait to send a value to a channel func main() { myChan := make(chan int) myChan <- 1 // deadlock fmt.Println("Hi everyone") }
- 14. www.eliftech.com Channel A goroutine can close a channel func sidekick(mChan chan<- string) { mChan <- "I have not so much to say" mChan <- "Sorry" close(mChan) } func main() { wfm := true var m string mChan := make(chan string) go sidekick(mChan) for { m, wfm = <-mChan if !wfm { break } fmt.Printf("Message from the sidekick: %sn", m) } fmt.Println("Thanks for your attention.") }
- 15. www.eliftech.com Channel A deadlock can occur when sending into channel func sidekick(taskChannel <-chan string) { task := <- taskChannel fmt.Printf(“Done: %sn”, task) fmt.Println(“Enough work for today”) } func main() { taskChannel := make(chan string) go sidekick(taskChannel) taskChannel <- “Wash the dishes” // deadlock taskChannel <- “Do laundry” }
- 16. www.eliftech.com Channel A channel can have a buffer func sidekick(taskChannel <-chan string) { task := <- taskChannel fmt.Printf(“Done: %sn”, task) fmt.Println(“Enough work for today”) } func main() { taskChannel := make(chan string, 1) go sidekick(taskChannel) taskChannel <- “Wash the dishes” taskChannel <- “Do laundry” }
- 17. www.eliftech.com Channel “select” waits for a value from a set of channels func sidekick() { task := <-taskChan time.Sleep(2 * time.Second) resChan <- fmt.Sprintf( "Done: %sn", task, ) } func main() { // channels initialization omitted go sidekick(taskChan, resChan) taskChan <- "Wash the dishes" timer := time.NewTimer(1 * time.Second) var res string select { ...
- 18. www.eliftech.com Channel “select” waits for a value from a set of channels func sidekick() { task := <-taskChan time.Sleep(2 * time.Second) resChan <- fmt.Sprintf( "Done: %sn", task, ) } ... select { case res = <- resChan: fmt.Println(res) case <- timer.C: fmt.Println("SIDEKICK!") fmt.Println("What are you doing?") } }
- 19. www.eliftech.com Channel anti-pattern Do not guard channels with mutexes. Channels don’t need concurrency control. They are concurrency control.
- 21. www.eliftech.com type sync.Mutex ▪ Mutual exclusion lock. ▪ Zero value is unlocked
- 22. www.eliftech.com type sync.WaitGroup Makes a goroutine block until some work is done
- 23. www.eliftech.com type sync.Mutex, type sync.WaitGroup var c = 0 var cMutex sync.Mutex var waitGroup sync.WaitGroup func sidekick() { cMutex.Lock() c ++ cMutex.Unlock() waitGroup.Done() } func main() { waitGroup.Add(n) for i := 0; i < n; i++ { go sidekick() } waitGroup.Wait() cMutex.Lock() fmt.Printf("Counter's value: %dn", c) cMutex.Unlock() }
- 24. www.eliftech.com type sync.RWMutex Reader / writer mutual exclusion lock. Many readers, single writer simultaneously type sync.Once Performs only one action only once
- 25. www.eliftech.com type sync.Pool type sync.Map type sync.Cond Thread-safe collection of temporary objects Map safe for concurrent use Condition object used to announce an event
- 26. www.eliftech.com runtime.GOMAXPROCS(int) int ▪ Function to set maximum number of native threads run simultaneously. ▪ Defaults to number of CPUs (since Go 1.6, previously defaulted to 1)
- 27. www.eliftech.com runtime.NumGoroutine() int Returns the number of goroutines that currently exist.
- 28. www.eliftech.com runtime.Gosched() Explicitly make Go scheduler switch contexts - let other goroutines run
- 29. www.eliftech.com Conclusion Go concurrency is cheap Go concurrency is complicated (as any concurrency) Go concurrency is powerful
- 30. www.eliftech.com Sources ▪ “Mastering concurrency in Go” by Nathan Kozyra ▪ Golang.org ▪ “Learning Go’s concurrency through illustrations” by Trevor Forrey ▪ “Go Antipatterns” at hackmongo.com
- 31. www.eliftech.com Don't forget to subscribe not to miss our next presentations! Find us at eliftech.com Have a question? Contact us: [email protected]