What is select?

Learn to wait on multiple channels with select.

What is select?

select waits on multiple channel operations at once. It looks like switch but each case is a channel operation. The ready case runs; if several are ready one is picked at random.

select lets a goroutine react to many events. It is the standard tool for timeouts, cancellation or multiple data sources.

select structure

A select block has cases. Each case is a channel operation: case v := <-ch1: or case ch2 <- 1:. The body of the ready case runs.

If no case is ready and there is a default, it runs; otherwise select blocks. If several cases are ready Go picks one at random; this gives fair scheduling.

Exercise Wait with select

Inside main, add a select { ... } block and print select ready with fmt.Println.

Show example solution

package main

import "fmt"

func main() {
    ch := make(chan string)
    go func() { ch <- "select hazır" }()
    select {
    case m := <-ch:
        fmt.Println(m)
    }
}

Test yourself

What does select wait on?
- Loops
- Multiple channels
- A single channel
- Errors
Show answer

Multiple channels — multiple channels. For one channel <-ch is enough.

select block

____ {
    case v := <-ch1:
        fmt.Println(v)
    case ch2 <- 1:
        fmt.Println("sent")
}

Show answer

select {
    case v := <-ch1:
        fmt.Println(v)
    case ch2 <- 1:
        fmt.Println("sent")
}

Match select concepts

select

Multi-wait
case

Channel op
default

When none ready
random

Several ready

Next lesson: Multiple channels

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