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Go Concurrency

Go Channels

Send values between goroutines with channels: unbuffered, buffered, close and range.

  • Advanced
  • 3 min read
  • 1 runnable example
What you'll learn
  • Send and receive
  • close and range
  • Buffered channels
Run code →
Producer to main
  1. 1out <- messageproducer goroutine
  2. 2chan stringstep 1, step 2, step 3
  3. 3range messagesmain

A pipe between goroutines

A channel is a pipe that carries values from one goroutine to another. Sending and receiving wait for each other, so channels also keep goroutines in step.

out <- value sends and <-channel receives. An unbuffered channel hands each message directly to the receiver. close tells the receiver that nothing more will come, which ends the range loop. A buffered channel holds up to its capacity without a receiver.

Key points

  1. ch <- v sends and <-ch receives.
  2. close ends a range loop.
  3. A buffered channel holds values without a receiver.

Runnable Go example

Go
Run code →
main.go
package main

import "fmt"

func produce(steps int, out chan<- string) {
	for step := 1; step <= steps; step++ {
		out <- fmt.Sprintf("step %d done", step)
	}
	close(out) // tells the receiver there is nothing more
}

func main() {
	messages := make(chan string)
	go produce(3, messages)

	for message := range messages {
		fmt.Println("received:", message)
	}

	buffered := make(chan int, 2)
	buffered <- 1
	buffered <- 2
	fmt.Println(len(buffered), <-buffered, <-buffered)
}
Get a Run button for this example Result of running the code
received: step 1 done
received: step 2 done
received: step 3 done
2 1 2

Practice

Open the example in the online compiler, change a value or add a line, and predict the output before you run it. Then break the code on purpose and read the compiler's message.

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