context with timeout

.go

package main

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

func main() {
	fmt.Println("testing time out")

	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()

	fmt.Println("before")

	go func() {
		time.Sleep(10 * time.Second)
		cancel()
	}()

	err := example(ctx)
	fmt.Println("---------")
	if err == context.Canceled {
		fmt.Println("done: cancelled")
	} else if err == context.DeadlineExceeded {
		fmt.Println("done: deadline_exceeded")
	} else if err != nil {
		fmt.Println("done: error")
	} else {
		fmt.Println("done: ok")
	}
}

func example(ctx context.Context) (err error) {
	ticker := time.NewTicker(time.Second)
	defer ticker.Stop()

	// count := 0

loop:
	for count := 0; ; count++ {
		select {
		case <-ctx.Done():
			fmt.Println("FINISH in <-ctx.Done()")
			err = ctx.Err()
			break loop
		case <-ticker.C:
			fmt.Println("HERE IN TICKER (waiting 2 sec)")

			// case finish: ok and error
			if count == 3 {
				fmt.Println("FINISH with count")
				err = errors.New("finish with error")
				break loop
			}
		}
	}

	fmt.Println("after the loop")
	return err
}

gistfile1.txt

➜ go run main.go
testing time out
before
HERE IN TICKER (waiting 2 sec)
HERE IN TICKER (waiting 2 sec)
HERE IN TICKER (waiting 2 sec)
HERE IN TICKER (waiting 2 sec)
FINISH with count
after the loop
---------
done: ok

++++++++++++++++++++++++++++++++++++++++

➜ go run main.go
testing time out
before
HERE IN TICKER (waiting 2 sec)
HERE IN TICKER (waiting 2 sec)
HERE IN TICKER (waiting 2 sec)
HERE IN TICKER (waiting 2 sec)
HERE IN TICKER (waiting 2 sec)
FINISH in <-ctx.Done()
after the loop
---------
done: deadline_exceeded

++++++++++++++++++++++++++++++++++++++++

➜ go run main.go
testing time out
before
HERE IN TICKER (waiting 2 sec)
HERE IN TICKER (waiting 2 sec)
FINISH in <-ctx.Done()
after the loop
---------
done: cancelled

+++++++++++++++++++++++++++++++++++++++++ 

➜ go run main.go
testing time out
before
HERE IN TICKER (waiting 2 sec)
HERE IN TICKER (waiting 2 sec)
HERE IN TICKER (waiting 2 sec)
HERE IN TICKER (waiting 2 sec)
FINISH with count
after the loop
---------
done: error