func ExampleWithTimeout() {
	ctx, cancel := context.WithTimeout(context.Background(), 50*time.Millisecond)
	defer cancel()
	select {
	case <-time.After(1 * time.Second):
		fmt.Println("overslept")
	case <-ctx.Done():
		fmt.Println(ctx.Err())  
	}
}
This example passes a context with a timeout to tell a blocking function that
it should abandon its work after the timeout elapses.
package context_test
import (
	"fmt"
	"time"
	"golang.org/x/net/context"
)