Go by Example: Waiting For Goroutines To Finish
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To wait for multiple goroutines to finish, we can use a sync.WaitGroup. |
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package main
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import (
"fmt"
"math/rand"
"sync"
"time"
)
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This is the function we’ll run in every goroutine. wg is the WaitGroup it uses to notify that it’s done. Note that a WaitGroup must be passed to functions by pointer. |
func worker(id int, wg *sync.WaitGroup) {
fmt.Printf("Worker %d starting\n", id)
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Sleep for a random duration between 500-700 ms to simulate work. See the random numbers example for more details on rand. |
msToSleep := time.Duration(500 + rand.Intn(200))
time.Sleep(msToSleep * time.Millisecond)
fmt.Printf("Worker %d done\n", id)
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Notify the WaitGroup that we’re done. |
wg.Done()
}
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func main() {
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This WaitGroup is used to wait for all the goroutines launched here to finish. |
var wg sync.WaitGroup
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Launch several goroutines and increment the WorkGroup counter for each. |
for i := 1; i <= 5; i++ {
wg.Add(1)
go worker(i, &wg)
}
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Block until the WorkGroup counter goes back to 0; all the workers notified they’re done. |
wg.Wait()
}
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$ go run waiting-for-goroutines-to-finish.go
Worker 5 starting
Worker 3 starting
Worker 4 starting
Worker 1 starting
Worker 2 starting
Worker 4 done
Worker 1 done
Worker 2 done
Worker 5 done
Worker 3 done
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The order of workers starting up and finishing is likely to be different for each invocation. |
Next example: Channel Directions.