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Mastering Concurrency in Go

Select Statement

This lesson will introduce you to multi-way concurrent control in Go: the select statement.

We'll cover the following...

The select statement blocks the code and waits for multiple channel opera­tions simul­taneously.

Syntax

The syntax for the select statement is as follows:

C++
select {   
  case channel operation:     
    statement(s);     
       . //more cases
       .
       .      
  default : //Optional
    statement(s); 
}

Example

Let’s try to understand the usage of a select statement with a simple example consisting of two channels which are communicating using send/receive operations:

Go (1.6.2)
package main
import (
	"fmt"
	"time"
)
func main() {
	channel1 := make(chan string)
	channel2 := make(chan string)
	go func() {
		for i := 0; i < 5; i++ {
			channel1 <- "I'll print every 100ms"
			time.Sleep(time.Millisecond * 100)
			
		}
	}()
	go func() {
		for i := 0; i < 5; i++ {
			channel2 <- "I'll print every 1s"
			time.Sleep(time.Second * 1)
			
		}
	}()
	for i := 0; i < 5; i++ {
		
		fmt.Println(<-channel1)
		fmt.Println(<-channel2)
		
	}
}

In the code above, we have two goroutines, each of which is sending messages on each of the two channels.

The first goroutine sends a message I'll print every 100ms and then waits for 100ms before sending the message again in the next iteration.

go func() {
	for i := 0; i < 5; i++
...