Merge from trunk revision 104c05c5284b7822d770ee51a7d91946c7e56d50.

3 files changed, 34 insertions, 16 deletions

diff --git a/libgo/go/context/benchmark_test.go b/libgo/go/context/benchmark_test.go
index 5d56863..69d75ff 100644
--- a/libgo/go/context/benchmark_test.go
+++ b/libgo/go/context/benchmark_test.go
@@ -138,3 +138,17 @@ func BenchmarkCheckCanceled(b *testing.B) {
 		}
 	})
 }
+
+func BenchmarkContextCancelDone(b *testing.B) {
+	ctx, cancel := WithCancel(Background())
+	defer cancel()
+
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			select {
+			case <-ctx.Done():
+			default:
+			}
+		}
+	})
+}
diff --git a/libgo/go/context/context.go b/libgo/go/context/context.go
index b3fdb82..733c5f5 100644
--- a/libgo/go/context/context.go
+++ b/libgo/go/context/context.go
@@ -303,10 +303,8 @@ func parentCancelCtx(parent Context) (*cancelCtx, bool) {
 	if !ok {
 		return nil, false
 	}
-	p.mu.Lock()
-	ok = p.done == done
-	p.mu.Unlock()
-	if !ok {
+	pdone, _ := p.done.Load().(chan struct{})
+	if pdone != done {
 		return nil, false
 	}
 	return p, true
@@ -345,7 +343,7 @@ type cancelCtx struct {
 	Context
 
 	mu       sync.Mutex            // protects following fields
-	done     chan struct{}         // created lazily, closed by first cancel call
+	done     atomic.Value          // of chan struct{}, created lazily, closed by first cancel call
 	children map[canceler]struct{} // set to nil by the first cancel call
 	err      error                 // set to non-nil by the first cancel call
 }
@@ -358,13 +356,18 @@ func (c *cancelCtx) Value(key interface{}) interface{} {
 }
 
 func (c *cancelCtx) Done() <-chan struct{} {
+	d := c.done.Load()
+	if d != nil {
+		return d.(chan struct{})
+	}
 	c.mu.Lock()
-	if c.done == nil {
-		c.done = make(chan struct{})
+	defer c.mu.Unlock()
+	d = c.done.Load()
+	if d == nil {
+		d = make(chan struct{})
+		c.done.Store(d)
 	}
-	d := c.done
-	c.mu.Unlock()
-	return d
+	return d.(chan struct{})
 }
 
 func (c *cancelCtx) Err() error {
@@ -401,10 +404,11 @@ func (c *cancelCtx) cancel(removeFromParent bool, err error) {
 		return // already canceled
 	}
 	c.err = err
-	if c.done == nil {
-		c.done = closedchan
+	d, _ := c.done.Load().(chan struct{})
+	if d == nil {
+		c.done.Store(closedchan)
 	} else {
-		close(c.done)
+		close(d)
 	}
 	for child := range c.children {
 		// NOTE: acquiring the child's lock while holding parent's lock.
diff --git a/libgo/go/context/context_test.go b/libgo/go/context/context_test.go
index 6b392a2..a2e2324 100644
--- a/libgo/go/context/context_test.go
+++ b/libgo/go/context/context_test.go
@@ -525,7 +525,7 @@ func XTestInterlockedCancels(t testingT) {
 	parent, cancelParent := WithCancel(Background())
 	child, cancelChild := WithCancel(parent)
 	go func() {
-		parent.Done()
+		<-parent.Done()
 		cancelChild()
 	}()
 	cancelParent()
@@ -661,7 +661,7 @@ func XTestWithCancelCanceledParent(t testingT) {
 		t.Errorf("child not done immediately upon construction")
 	}
 	if got, want := c.Err(), Canceled; got != want {
-		t.Errorf("child not cancelled; got = %v, want = %v", got, want)
+		t.Errorf("child not canceled; got = %v, want = %v", got, want)
 	}
 }
 
@@ -779,7 +779,7 @@ func XTestCustomContextGoroutines(t testingT) {
 	defer cancel6()
 	checkNoGoroutine()
 
-	// Check applied to cancelled context.
+	// Check applied to canceled context.
 	cancel6()
 	cancel1()
 	_, cancel7 := WithCancel(ctx5)