Fix test race: Atomically access minConnecTimout in testing environme…

…nt. (grpc#1897)

clientconn.go

@@ -45,6 +45,11 @@ import (
 	"google.golang.org/grpc/transport"
 )
 
+const (
+	// minimum time to give a connection to complete
+	minConnectTimeout = 20 * time.Second
+)
+
 var (
 	// ErrClientConnClosing indicates that the operation is illegal because
 	// the ClientConn is closing.
@@ -60,8 +65,11 @@ var (
 	errConnUnavailable = errors.New("grpc: the connection is unavailable")
 	// errBalancerClosed indicates that the balancer is closed.
 	errBalancerClosed = errors.New("grpc: balancer is closed")
-	// minimum time to give a connection to complete
-	minConnectTimeout = 20 * time.Second
+	// We use an accessor so that minConnectTimeout can be
+	// atomically read and updated while testing.
+	getMinConnectTimeout = func() time.Duration {
+		return minConnectTimeout
+	}
 )
 
 // The following errors are returned from Dial and DialContext
@@ -1055,7 +1063,7 @@ func (ac *addrConn) resetTransport() error {
 			// connection.
 			backoffFor := ac.dopts.bs.backoff(connectRetryNum) // time.Duration.
 			// This will be the duration that dial gets to finish.
-			dialDuration := minConnectTimeout
+			dialDuration := getMinConnectTimeout()
 			if backoffFor > dialDuration {
 				// Give dial more time as we keep failing to connect.
 				dialDuration = backoffFor

clientconn_test.go

@@ -39,6 +39,16 @@ import (
 	"google.golang.org/grpc/testdata"
 )
 
+var (
+	mutableMinConnectTimeout = time.Second * 20
+)
+
+func init() {
+	getMinConnectTimeout = func() time.Duration {
+		return time.Duration(atomic.LoadInt64((*int64)(&mutableMinConnectTimeout)))
+	}
+}
+
 func assertState(wantState connectivity.State, cc *ClientConn) (connectivity.State, bool) {
 	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
 	defer cancel()
@@ -169,13 +179,14 @@ func TestDialWaitsForServerSettings(t *testing.T) {
 }
 
 func TestCloseConnectionWhenServerPrefaceNotReceived(t *testing.T) {
-	mctBkp := minConnectTimeout
+	mctBkp := getMinConnectTimeout()
 	// Call this only after transportMonitor goroutine has ended.
 	defer func() {
-		minConnectTimeout = mctBkp
+		atomic.StoreInt64((*int64)(&mutableMinConnectTimeout), int64(mctBkp))
+
 	}()
 	defer leakcheck.Check(t)
-	minConnectTimeout = time.Millisecond * 500
+	atomic.StoreInt64((*int64)(&mutableMinConnectTimeout), int64(time.Millisecond)*500)
 	lis, err := net.Listen("tcp", "localhost:0")
 	if err != nil {
 		t.Fatalf("Error while listening. Err: %v", err)