How can I sleep with responsive context cancelation?

Question

In Go, I want to time.Sleep for some time (e.g. waiting between retries), but want to return quickly if the context gets canceled (not just from a deadline, but also manually).

What is the right or best way to do that? Thanks!

Answer 1

You can use select to acheive this:

package main

import (
    "fmt"
    "time"
    "context"
)

func main() {
    fmt.Println("Hello, playground")
    ctx, cancel := context.WithCancel(context.Background())
    defer cancel()
    go func(){
        t := time.Now()
        select{
        case <-ctx.Done(): //context cancelled
        case <-time.After(2 * time.Second): //timeout
        }
        fmt.Printf("here after: %v\n", time.Since(t))
    }()

    cancel() //cancel manually, comment out to see timeout kick in
    time.Sleep(3 * time.Second)
    fmt.Println("done")

}

Here is the Go-playground link

Answer 2

Here is a sleepContext function that you can use instead of time.Sleep:

func sleepContext(ctx context.Context, delay time.Duration) {
    select {
    case <-ctx.Done():
    case <-time.After(delay):
    }
}

And some sample usage (full runnable code on the Go Playground):

func main() {
    ctx := context.Background()

    fmt.Println(time.Now())
    sleepContext(ctx, 1*time.Second)
    fmt.Println(time.Now())

    ctxTimeout, cancel := context.WithTimeout(ctx, 500*time.Millisecond)
    sleepContext(ctxTimeout, 1*time.Second)
    cancel()
    fmt.Println(time.Now())
}