Merge pull request #8871 from tonistiigi/start-wait-hijack

Wait for hijack on docker start command

api/client/commands.go

@@ -627,6 +627,8 @@ func (cli *DockerCli) CmdStart(args ...string) error {
 		return nil
 	}
 
+	hijacked := make(chan io.Closer)
+
 	if *attach || *openStdin {
 		if cmd.NArg() > 1 {
 			return fmt.Errorf("You cannot start and attach multiple containers at once.")
@@ -663,8 +665,24 @@ func (cli *DockerCli) CmdStart(args ...string) error {
 		v.Set("stderr", "1")
 
 		cErr = promise.Go(func() error {
-			return cli.hijack("POST", "/containers/"+cmd.Arg(0)+"/attach?"+v.Encode(), tty, in, cli.out, cli.err, nil, nil)
+			return cli.hijack("POST", "/containers/"+cmd.Arg(0)+"/attach?"+v.Encode(), tty, in, cli.out, cli.err, hijacked, nil)
 		})
+	} else {
+		close(hijacked)
+	}
+
+	// Acknowledge the hijack before starting
+	select {
+	case closer := <-hijacked:
+		// Make sure that the hijack gets closed when returning (results
+		// in closing the hijack chan and freeing server's goroutines)
+		if closer != nil {
+			defer closer.Close()
+		}
+	case err := <-cErr:
+		if err != nil {
+			return err
+		}
 	}
 
 	var encounteredError error