Add a flag to prevent launching twice.

lib/launcher/error.go

@@ -0,0 +1,6 @@
+package launcher
+
+import "errors"
+
+// ErrAlreadyLaunched is an error that indicates the launcher has already been launched.
+var ErrAlreadyLaunched = errors.New("already launched")

lib/launcher/launcher.go

@@ -13,6 +13,7 @@ import (
 	"path/filepath"
 	"sort"
 	"strings"
+	"sync/atomic"
 
 	"github.com/go-rod/rod/lib/defaults"
 	"github.com/go-rod/rod/lib/launcher/flags"
@@ -39,6 +40,8 @@ type Launcher struct {
 
 	managed    bool
 	serviceURL string
+
+	isLaunched int32 // zero means not launched
 }
 
 // New returns the default arguments to start browser.
@@ -377,7 +380,13 @@ func (l *Launcher) MustLaunch() string {
 // Launch a standalone temp browser instance and returns the debug url.
 // bin and profileDir are optional, set them to empty to use the default values.
 // If you want to reuse sessions, such as cookies, set the [Launcher.UserDataDir] to the same location.
+//
+// Please note launcher can only be used once.
 func (l *Launcher) Launch() (string, error) {
+	if l.hasLaunched() {
+		return "", ErrAlreadyLaunched
+	}
+
 	defer l.ctxCancel()
 
 	bin, err := l.getBin()
@@ -430,6 +439,10 @@ func (l *Launcher) Launch() (string, error) {
 	return ResolveURL(u)
 }
 
+func (l *Launcher) hasLaunched() bool {
+	return !atomic.CompareAndSwapInt32(&l.isLaunched, 0, 1)
+}
+
 func (l *Launcher) setupCmd(cmd *exec.Cmd) {
 	l.osSetupCmd(cmd)
 

lib/launcher/launcher_test.go

@@ -310,3 +310,17 @@ func TestBrowserDownloadErr(t *testing.T) {
 	}}
 	g.Err(b.Download())
 }
+
+func TestLaunchMultiTimes(t *testing.T) {
+	g := setup(t)
+
+	// first time launch, success.
+	l := launcher.New()
+	u, e := l.Launch()
+	g.Neq(u, "")
+	g.E(e)
+
+	// second time launch, failed with ErrAlreadyLaunched.
+	_, e = l.Launch()
+	g.Eq(e, launcher.ErrAlreadyLaunched)
+}