How to Close Channel in Go: Syntax and Examples

In Go, you close a channel using the built-in close() function by passing the channel as an argument, like close(ch). Closing a channel signals that no more values will be sent on it, allowing receivers to detect this and stop waiting.

Syntax

The syntax to close a channel in Go is simple. Use the close() function with the channel variable inside the parentheses.

• close(ch): Closes the channel ch.
• Only the sender should close the channel.
• Receivers can still receive remaining values until the channel is empty.

go

close(ch)

Example

This example shows how to create a channel, send values, close it, and receive values until the channel is empty.

go

package main

import "fmt"

func main() {
    ch := make(chan int)

    go func() {
        for i := 1; i <= 3; i++ {
            ch <- i
        }
        close(ch) // Close the channel after sending
    }()

    for val := range ch {
        fmt.Println(val)
    }
    fmt.Println("Channel closed, no more values.")
}

Output

1
2
3
Channel closed, no more values.

Common Pitfalls

Common mistakes when closing channels include:

• Closing a channel more than once causes a panic.
• Closing a channel from the receiver side instead of the sender.
• Sending on a closed channel causes a panic.

Always let the sender close the channel and never send after closing.

go

package main

import "fmt"

func main() {
    ch := make(chan int)

    // Wrong: closing channel twice causes panic
    close(ch)
    // close(ch) // Uncommenting this line will cause panic: close of closed channel

    // Wrong: sending on closed channel causes panic
    // ch <- 1 // Uncommenting this line will cause panic

    fmt.Println("Avoid these mistakes.")
}

Output

Avoid these mistakes.

Quick Reference

Remember these key points when working with channels and closing them:

• Use close(ch) to close a channel.
• Only the sender should close the channel.
• Do not send on a closed channel.
• Receivers can detect closed channels using for val := range ch or by checking the second value from receive.

Key Takeaways

Use close(ch) to close a channel when no more values will be sent.

Only the sender should close the channel to avoid panics.

Do not send values on a closed channel; it causes a runtime panic.

Receivers can detect closed channels by ranging over them or checking the second boolean value.

Closing a channel signals receivers that no more data is coming.