Go by Example: WaitGroup
+ +|
+ To wait for multiple goroutines to finish, we can +use a wait group. + + |
+ + + + | +
| + + | +
+ 
+ package main
+ |
+
| + + | +
+
+ import (
+ "fmt"
+ "sync"
+ "time"
+)
+ |
+
|
+ 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) {
+ fmt.Printf("Worker %d starting\n", id)
+ |
+
|
+ Sleep to simulate an expensive task. + + |
+
+
+ time.Sleep(time.Second)
+ fmt.Printf("Worker %d done\n", id)
+ |
+
|
+ Notify the WaitGroup that we’re done. + + |
+
+
+ wg.Done()
+}
+ |
+
| + + | +
+
+ func main() {
+ |
+
|
+ This WaitGroup is used to wait for all the +goroutines launched here to finish. + + |
+
+
+ var wg sync.WaitGroup
+ |
+
|
+ Launch several goroutines and increment the WorkGroup +counter for each. + + |
+
+
+ for i := 1; i <= 5; i++ {
+ wg.Add(1)
+ go worker(i, &wg)
+ }
+ |
+
|
+ Block until the WorkGroup counter goes back to 0; +all the workers notified they’re done. + + |
+
+
+ wg.Wait()
+}
+ |
+
| + + | +
+
+ $ go run waitgroup.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
+ |
+
|
+ The order of workers starting up and finishing +is likely to be different for each invocation. + + |
+ + + + | +
+ Next example: Rate Limiting. +
+ + +