Exiting Multiple Goroutines Simultaneously

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The ability to close channels (using Go’s builtin close() function) forms the basis of a useful pattern in Go: using a single channel to exit multiple goroutines.

Let’s say we have launched a variable number of goroutines in the background as follows:

shutdown := make(chan struct{})
done := make(chan int)

for i := 0; i < n; i++ {
	i := i
	go func() {
		select {
		case <-shutdown:
			done <- i
		}
	}()
}

Once started, each goroutine will wait for a signal from a single shutdown channel before exiting. We would like to signal all n goroutines to be shut down at once in the most elegant way possible. To do so, we can make use of the fact that receiving on a closed channel will never block. Simply by closing the shutdown channel, we can signal all goroutines to “unblock,” causing them to immediately exit. A complete example is given below:

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package main

import (
"fmt"
"time"
)

var (
shutdown = make(chan struct{})
done = make(chan int)
)

func main() {
const n = 5

// Start up the goroutines...
for i := 0; i < n; i++ {
i := i
go func() {
select {
case <-shutdown:
done <- i
}
}()
}

time.Sleep(2 * time.Second)

// Close the channel. All goroutines will immediately "unblock".
close(shutdown)

for i := 0; i < n; i++ {
fmt.Println("routine", <-done, "has exited!")
}
}

You can also view and run the above example on the Go Playground.

Let me know if you found this pattern helpful in the comments below, and don’t forget to +1 this post!

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