Goroutines¶

• Creating goroutines
  • Use go keyword in front of function call
  • When using anonymous functions, pass data as local variables
• Synchronization
  • Use sync.WaitGroup to wait for groups of goroutines to complete
  • Use sync.Mutex and sync.RWMutes to protect data access
• Parallelism
  • By default, Go will use CPU threads equal to available cores
  • Change with runtime.GOMAXPROCS
  • More threads can increase performance, but too many can slow it down
• Best Practices
  • Don't create goroutines in libraries
    • Let consumer control concurrency
  • When creating a goroutine, know how it will end
    • Avoids subtle memory leaks

  • Check for race conditions at compile time ``` ➜ daviskregers git:(master) ✗ go run -race ./13_goroutines/Main.go Hello #0 ================== WARNING: DATA RACE Write at 0x0000005fe178 by goroutine 8: main.increment() /home/davis/projects/learning/golang/src/github.com/daviskregers/13_goroutines/Main.go:46 +0x5a

    Previous read at 0x0000005fe178 by goroutine 7: main.sayHello() /home/davis/projects/learning/golang/src/github.com/daviskregers/13_goroutines/Main.go:35 +0x3e

    Goroutine 8 (running) created at: main.main() /home/davis/projects/learning/golang/src/github.com/daviskregers/13_goroutines/Main.go:17 +0x80

    Goroutine 7 (finished) created at: main.main() /home/davis/projects/learning/golang/src/github.com/daviskregers/13_goroutines/Main.go:16 +0x68 ================== Hello #1 Hello #2 Hello #3 Hello #4 Hello #5 Hello #6 Hello #7 Hello #8 Hello #9 Threads: 8 Hello #10 Hello #11 Hello #12 Hello #13 Hello #14 Hello #15 Hello #16 Hello #17 Hello #18 Hello #19 Found 1 data race(s) exit status 66

    ```

package main

import (
        "fmt"
        "runtime"
        "sync"
)

var wg = sync.WaitGroup{}
var counter = 0
var m = sync.RWMutex{}

func main() {
    for i := 0; i < 10; i++ {
        wg.Add(2)
        go sayHello()
        go increment()
    }
    wg.Wait()

   // 
   fmt.Printf("Threads: %v\n", runtime.GOMAXPROCS(-1))
   for i := 0; i < 10; i++ {
       wg.Add(2)
       m.RLock()
       go sayHelloM()
       m.Lock()
       go incrementM()
   }
   wg.Wait()

}

func sayHello() {
    fmt.Printf("Hello #%v\n", counter)
    wg.Done()
}

func sayHelloM() {
    fmt.Printf("Hello #%v\n", counter)
    m.RUnlock()
    wg.Done()
}

func increment() {
    counter++
    wg.Done()
}

func incrementM() {
    counter++
    m.Unlock()
    wg.Done()
}

Hello #2
Hello #4
Hello #0
Hello #2
Hello #5
Hello #5
Hello #7
Hello #8
Hello #8
Hello #9
Threads: 8
Hello #10
Hello #11
Hello #12
Hello #13
Hello #14
Hello #15
Hello #16
Hello #17
Hello #18
Hello #19