Go by Example: WaitGroups
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To wait for multiple goroutines to finish, we can use a wait group. |
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package main |
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import ( "fmt" "sync" "time" ) |
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This is the function we’ll run in every goroutine. Note that a WaitGroup must be passed to functions by pointer. |
func worker(id int, wg *sync.WaitGroup) { |
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On return, notify the WaitGroup that we’re done. |
defer wg.Done()
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fmt.Printf("Worker %d starting\n", id) |
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Sleep to simulate an expensive task. |
time.Sleep(time.Second)
fmt.Printf("Worker %d done\n", id)
}
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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 WaitGroup counter for each. |
for i := 1; i <= 5; i++ {
wg.Add(1)
go worker(i, &wg)
}
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Block until the WaitGroup counter goes back to 0; all the workers notified they’re done. |
wg.Wait()
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Note that this approach has no straightforward way to propagate errors from workers. For more advanced use cases, consider using the errgroup package. |
}
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$ go run waitgroups.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: Rate Limiting.