WaitGroups

Context

sync.WaitGroup waits for a collection of goroutines to finish. Use Add to set the count, Done to decrement, and Wait to block until the count reaches zero.

Example

Start three goroutines and wait for all to complete.

Code example

package main

import (
    "fmt"
    "sync"
    "time"
)

func worker(id int, wg *sync.WaitGroup) {
    defer wg.Done()
    fmt.Printf("Worker %d starting\n", id)
    time.Sleep(time.Second)
    fmt.Printf("Worker %d done\n", id)
}

func main() {
    var wg sync.WaitGroup
    for i := 1; i <= 3; i++ {
        wg.Add(1)
        go worker(i, &wg)
    }
    wg.Wait()
    fmt.Println("All workers finished")
}

Output

Worker 3 starting
Worker 1 starting
Worker 2 starting
Worker 2 done
Worker 1 done
Worker 3 done
All workers finished

Useful links

• sync.WaitGroup documentation
• Go by Example: WaitGroups