add util.CancellationChild() and run gofmt

src/util/cancellation.go

@@ -2,9 +2,9 @@ package util
 
 import (
 	"errors"
+	"runtime"
 	"sync"
 	"time"
-  "runtime"
 )
 
 type Cancellation interface {
@@ -63,14 +63,25 @@ func (c *cancellation) Error() error {
 	return err
 }
 
-func CancellationWithTimeout(parent Cancellation, timeout time.Duration) Cancellation {
+func CancellationChild(parent Cancellation) Cancellation {
 	child := NewCancellation()
+	go func() {
+		select {
+		case <-child.Finished():
+		case <-parent.Finished():
+			child.Cancel(parent.Error())
+		}
+	}()
+	return child
+}
+
+func CancellationWithTimeout(parent Cancellation, timeout time.Duration) Cancellation {
+	child := CancellationChild(parent)
 	go func() {
 		timer := time.NewTimer(timeout)
 		defer TimerStop(timer)
 		select {
-    case <-parent.Finished():
-      child.Cancel(parent.Error())
+		case <-child.Finished():
 		case <-timer.C:
 			child.Cancel(errors.New("timeout"))
 		}