Closing a channel
- Go course
- Intermediate
- Lesson 17/80
- 4 min
Learn to close a channel with close and detect closure.
Closing a channel
You close a channel with close(ch). Sending on a closed channel panics; receiving from a closed channel returns the zero value. This is how you signal that no more data will come.
With v, ok := <-ch you learn if the channel is open. If ok is false the channel is closed and drained. The for v := range ch loop ends automatically when the channel closes.
close and range
Closing a channel pairs with for v := range ch. The sender calls close(ch) after all data is sent; the receiver's range loop ends automatically.
The sender, not the receiver, should close the channel; if the receiver closes it the sender may panic. Following this principle is key for safe concurrency.
Practice Close a channel and print
Inside main, add a make(chan string) call and print closed with fmt.Println.
Starter code
package main
import "fmt"
func main() {
// buraya yaz
}Sample solution
package main
import "fmt"
func main() {
ch := make(chan string, 1)
ch <- "kapatıldı"
close(ch)
fmt.Println(<-ch)
}Expected output
kapatıldı
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What happens when you send on a closed channel?
- Silently ignored
- It panics Correct answer
- It blocks
- Returns zero value
Explanation: it panics. RECEIVING from a closed channel returns zero value.
2 Closing a channel
ch := make(chan int, 2)
ch <- 1
ch <- 2
____
for v := range ch {
fmt.Println(v)
}ch := make(chan int, 2)
ch <- 1
ch <- 2
close(ch)
for v := range ch {
fmt.Println(v)
}Explanation: In Go close is a function, not a method.
3 Match close concepts
| Term | Meaning |
|---|---|
close(ch) |
Close |
v, ok |
Status |
range |
Auto-end |
panic |
Send on closed |