Closing Channels
fmtClosing a channel indicates that no more values will be sent on it. This can be useful to communicate completion to the channel's receivers.
package main
import "fmt"In this example we'll use a jobs channel to communicate work to be done from the main goroutine to a worker goroutine. When we have no more jobs for the worker we'll close the jobs channel.
func main() {
jobs := make(chan int, 5)
done := make(chan bool)Here's the worker goroutine. It repeatedly receives from jobs with j, more := <-jobs. In this special 2-value form of receive, the more value will be false if jobs has been closed and all values in the channel have already been received. We use this to notify on done when we've worked all our jobs.
go func() {
for {
j, more := <-jobs
if more {
fmt.Println("received job", j)
} else {
fmt.Println("received all jobs")
done <- true
return
}
}
}()This sends 3 jobs to the worker over the jobs channel, then closes it.
for j := 1; j <= 3; j++ {
jobs <- j
fmt.Println("sent job", j)
}
close(jobs)
fmt.Println("sent all jobs")We await the worker using the synchronization approach we saw earlier.
<-doneReading from a closed channel succeeds immediately, returning the zero value of the underlying type.
_, ok := <-jobs
fmt.Println("received more jobs:", ok)Sending on a closed channel panics, so only the sender should close it.
defer func() { fmt.Println("recovered:", recover()) }()
jobs <- 4
}$ go run ./40_closing_channels sent job 1 sent job 2 sent job 3 sent all jobs received job 1 received job 2 received job 3 received all jobs received more jobs: false recovered: send on closed channel