Fix bufconn.Close to not be blocking. (#1377)

test/bufconn/bufconn.go

@@ -31,10 +31,10 @@ import (
 // Listener implements a net.Listener that creates local, buffered net.Conns
 // via its Accept and Dial method.
 type Listener struct {
-	mu     sync.Mutex
-	sz     int
-	ch     chan net.Conn
-	closed bool
+	mu   sync.Mutex
+	sz   int
+	ch   chan net.Conn
+	done chan struct{}
 }
 
 var errClosed = fmt.Errorf("Closed")
@@ -42,28 +42,31 @@ var errClosed = fmt.Errorf("Closed")
 // Listen returns a Listener that can only be contacted by its own Dialers and
 // creates buffered connections between the two.
 func Listen(sz int) *Listener {
-	return &Listener{sz: sz, ch: make(chan net.Conn)}
+	return &Listener{sz: sz, ch: make(chan net.Conn), done: make(chan struct{})}
 }
 
 // Accept blocks until Dial is called, then returns a net.Conn for the server
 // half of the connection.
 func (l *Listener) Accept() (net.Conn, error) {
-	c := <-l.ch
-	if c == nil {
+	select {
+	case <-l.done:
 		return nil, errClosed
+	case c := <-l.ch:
+		return c, nil
 	}
-	return c, nil
 }
 
 // Close stops the listener.
 func (l *Listener) Close() error {
 	l.mu.Lock()
 	defer l.mu.Unlock()
-	if l.closed {
-		return nil
+	select {
+	case <-l.done:
+		// Already closed.
+		break
+	default:
+		close(l.done)
 	}
-	l.closed = true
-	close(l.ch)
 	return nil
 }
 
@@ -74,14 +77,13 @@ func (l *Listener) Addr() net.Addr { return addr{} }
 // providing it the server half of the connection, and returns the client half
 // of the connection.
 func (l *Listener) Dial() (net.Conn, error) {
-	l.mu.Lock()
-	defer l.mu.Unlock()
-	if l.closed {
-		return nil, errClosed
-	}
 	p1, p2 := newPipe(l.sz), newPipe(l.sz)
-	l.ch <- &conn{p1, p2}
-	return &conn{p2, p1}, nil
+	select {
+	case <-l.done:
+		return nil, errClosed
+	case l.ch <- &conn{p1, p2}:
+		return &conn{p2, p1}, nil
+	}
 }
 
 type pipe struct {

test/bufconn/bufconn_test.go

@@ -115,3 +115,35 @@ func TestListener(t *testing.T) {
 		t.Fatalf(err.Error())
 	}
 }
+
+func TestCloseWhileDialing(t *testing.T) {
+	l := Listen(7)
+	var c net.Conn
+	var err error
+	done := make(chan struct{})
+	go func() {
+		c, err = l.Dial()
+		close(done)
+	}()
+	l.Close()
+	<-done
+	if c != nil || err != errClosed {
+		t.Fatalf("c, err = %v, %v; want nil, %v", c, err, errClosed)
+	}
+}
+
+func TestCloseWhileAccepting(t *testing.T) {
+	l := Listen(7)
+	var c net.Conn
+	var err error
+	done := make(chan struct{})
+	go func() {
+		c, err = l.Accept()
+		close(done)
+	}()
+	l.Close()
+	<-done
+	if c != nil || err != errClosed {
+		t.Fatalf("c, err = %v, %v; want nil, %v", c, err, errClosed)
+	}
+}