add util.CancellationChild() and run gofmt

src/util/cancellation.go

@@ -1,83 +1,94 @@
 package util
 
 import (
-  "errors"
-  "sync"
-  "time"
-  "runtime"
+	"errors"
+	"runtime"
+	"sync"
+	"time"
 )
 
 type Cancellation interface {
-  Finished() <-chan struct{}
-  Cancel(error) error
-  Error() error
+	Finished() <-chan struct{}
+	Cancel(error) error
+	Error() error
 }
 
 func CancellationFinalizer(c Cancellation) {
-  c.Cancel(errors.New("finalizer called"))
+	c.Cancel(errors.New("finalizer called"))
 }
 
 type cancellation struct {
-  signal chan error
-  cancel chan struct{}
-  errMtx sync.RWMutex
-  err error
+	signal chan error
+	cancel chan struct{}
+	errMtx sync.RWMutex
+	err    error
 }
 
 func (c *cancellation) worker() {
-    // Launch this in a separate goroutine when creating a cancellation
-    err := <-c.signal
-    c.errMtx.Lock()
-    c.err = err
-    c.errMtx.Unlock()
-    close(c.cancel)
+	// Launch this in a separate goroutine when creating a cancellation
+	err := <-c.signal
+	c.errMtx.Lock()
+	c.err = err
+	c.errMtx.Unlock()
+	close(c.cancel)
 }
 
 func NewCancellation() Cancellation {
-  c := cancellation{
-    signal: make(chan error),
-    cancel: make(chan struct{}),
-  }
-  runtime.SetFinalizer(&c, CancellationFinalizer)
-  go c.worker()
-  return &c
+	c := cancellation{
+		signal: make(chan error),
+		cancel: make(chan struct{}),
+	}
+	runtime.SetFinalizer(&c, CancellationFinalizer)
+	go c.worker()
+	return &c
 }
 
 func (c *cancellation) Finished() <-chan struct{} {
-  return c.cancel
+	return c.cancel
 }
 
 func (c *cancellation) Cancel(err error) error {
-  select {
-  case c.signal<-err:
-    return nil
-  case <-c.cancel:
-    return c.Error()
-  }
+	select {
+	case c.signal <- err:
+		return nil
+	case <-c.cancel:
+		return c.Error()
+	}
 }
 
 func (c *cancellation) Error() error {
-  c.errMtx.RLock()
-  err := c.err
-  c.errMtx.RUnlock()
-  return err
+	c.errMtx.RLock()
+	err := c.err
+	c.errMtx.RUnlock()
+	return err
+}
+
+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 := NewCancellation()
-  go func() {
-    timer := time.NewTimer(timeout)
-    defer TimerStop(timer)
-    select {
-    case <-parent.Finished():
-      child.Cancel(parent.Error())
-    case <-timer.C:
-      child.Cancel(errors.New("timeout"))
-    }
-  }()
-  return child
+	child := CancellationChild(parent)
+	go func() {
+		timer := time.NewTimer(timeout)
+		defer TimerStop(timer)
+		select {
+		case <-child.Finished():
+		case <-timer.C:
+			child.Cancel(errors.New("timeout"))
+		}
+	}()
+	return child
 }
 
 func CancellationWithDeadline(parent Cancellation, deadline time.Time) Cancellation {
-  return CancellationWithTimeout(parent, deadline.Sub(time.Now()))
+	return CancellationWithTimeout(parent, deadline.Sub(time.Now()))
 }