Learn X By Example
Learn X By Example

    Go by Example: Select

    Go by Example : Select

    Go’s select lets you wait on multiple channel operations. Combining goroutines and channels with select is a powerful feature of Go.

    package main
    import (
    "fmt"
    "time"
)
    func main() {

    For our example we’ll select across two channels.

        c1 := make(chan string)
    c2 := make(chan string)

    Each channel will receive a value after some amount of time, to simulate e.g. blocking RPC operations executing in concurrent goroutines.

        go func() {
        time.Sleep(1 * time.Second)
        c1 <- "one"
    }()
    go func() {
        time.Sleep(2 * time.Second)
        c2 <- "two"
    }()

    We’ll use select to await both of these values simultaneously, printing each one as it arrives.

        for i := 0; i < 2; i++ {
        select {
        case msg1 := <-c1:
            fmt.Println("received", msg1)
        case msg2 := <-c2:
            fmt.Println("received", msg2)
        }
    }
}

    We receive the values "one" and then "two" as expected.

    $ time go run select.go 
received one
received two

    Note that the total execution time is only ~2 seconds since both the 1 and 2 second Sleeps execute concurrently.

    real    0m2.245s

    Next example: Timeouts .

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