From a806229364c4a668231a8b0b490ef94a63e44e0a Mon Sep 17 00:00:00 2001
From: Nuno Cruces <ncruces@users.noreply.github.com>
Date: Mon, 13 Sep 2021 13:17:15 +0100
Subject: [PATCH] Avoid closures in syscall.NewCallback, #20.

---
 file_windows.go | 14 ++++++++------
 msg_test.go     |  9 +++++++++
 msg_windows.go  | 43 +++++++++++++++++++++++--------------------
 util_windows.go | 30 ++++++++++++++++--------------
 4 files changed, 56 insertions(+), 40 deletions(-)

diff --git a/file_windows.go b/file_windows.go
index aac4577..d80a950 100644
--- a/file_windows.go
+++ b/file_windows.go
@@ -316,12 +316,7 @@ func browseForFolder(opts options) (string, []string, error) {
 	}
 	if opts.filename != "" {
 		args.LParam = strptr(opts.filename)
-		args.CallbackFunc = syscall.NewCallback(func(wnd uintptr, msg uint32, lparam, data uintptr) uintptr {
-			if msg == 1 { // BFFM_INITIALIZED
-				sendMessage.Call(wnd, 1024+103 /* BFFM_SETSELECTIONW */, 1 /* TRUE */, data)
-			}
-			return 0
-		})
+		args.CallbackFunc = syscall.NewCallback(browseForFolderCallback)
 		defer runtime.KeepAlive(opts.filename)
 	}
 
@@ -349,6 +344,13 @@ func browseForFolder(opts options) (string, []string, error) {
 	return str, []string{str}, nil
 }
 
+func browseForFolderCallback(wnd uintptr, msg uint32, lparam, data uintptr) uintptr {
+	if msg == 1 { // BFFM_INITIALIZED
+		sendMessage.Call(wnd, 1024+103 /* BFFM_SETSELECTIONW */, 1 /* TRUE */, data)
+	}
+	return 0
+}
+
 func initDirNameExt(filename string, name []uint16) (dir *uint16, ext *uint16) {
 	d, n := splitDirAndName(filename)
 	e := filepath.Ext(n)
diff --git a/msg_test.go b/msg_test.go
index bd787dd..af122d8 100644
--- a/msg_test.go
+++ b/msg_test.go
@@ -132,3 +132,12 @@ func TestMessage_script(t *testing.T) {
 		})
 	}
 }
+
+func TestMessage_callbacks(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+
+	for i := 0; i < 2000; i++ {
+		zenity.Error("text", zenity.Context(ctx))
+	}
+}
diff --git a/msg_windows.go b/msg_windows.go
index 26a740c..6df6ad5 100644
--- a/msg_windows.go
+++ b/msg_windows.go
@@ -79,25 +79,28 @@ func message(kind messageKind, text string, opts options) error {
 func hookMessageLabels(kind messageKind, opts options) (unhook context.CancelFunc, err error) {
 	return hookDialog(opts.ctx, func(wnd uintptr) {
 		enumChildWindows.Call(wnd,
-			syscall.NewCallback(func(wnd, lparam uintptr) uintptr {
-				var name [8]uint16
-				getClassName.Call(wnd, uintptr(unsafe.Pointer(&name)), uintptr(len(name)))
-				if syscall.UTF16ToString(name[:]) == "Button" {
-					ctl, _, _ := getDlgCtrlID.Call(wnd)
-					var text *string
-					switch ctl {
-					case 1, 6: // IDOK, IDYES
-						text = opts.okLabel
-					case 2: // IDCANCEL
-						text = opts.cancelLabel
-					case 7: // IDNO
-						text = opts.extraButton
-					}
-					if text != nil {
-						setWindowText.Call(wnd, strptr(*text))
-					}
-				}
-				return 1
-			}), 0)
+			syscall.NewCallback(hookMessageLabelsCallback),
+			uintptr(unsafe.Pointer(&opts)))
 	})
 }
+
+func hookMessageLabelsCallback(wnd uintptr, lparam *options) uintptr {
+	var name [8]uint16
+	getClassName.Call(wnd, uintptr(unsafe.Pointer(&name)), uintptr(len(name)))
+	if syscall.UTF16ToString(name[:]) == "Button" {
+		ctl, _, _ := getDlgCtrlID.Call(wnd)
+		var text *string
+		switch ctl {
+		case 1, 6: // IDOK, IDYES
+			text = lparam.okLabel
+		case 2: // IDCANCEL
+			text = lparam.cancelLabel
+		case 7: // IDNO
+			text = lparam.extraButton
+		}
+		if text != nil {
+			setWindowText.Call(wnd, strptr(*text))
+		}
+	}
+	return 1
+}
diff --git a/util_windows.go b/util_windows.go
index 875e044..a406ad7 100644
--- a/util_windows.go
+++ b/util_windows.go
@@ -90,21 +90,13 @@ func strptr(s string) uintptr {
 }
 
 func setup() context.CancelFunc {
-	var hwnd uintptr
-	enumWindows.Call(syscall.NewCallback(func(wnd, lparam uintptr) uintptr {
-		var pid uintptr
-		getWindowThreadProcessId.Call(wnd, uintptr(unsafe.Pointer(&pid)))
-		if int(pid) == os.Getpid() {
-			hwnd = wnd
-			return 0
-		}
-		return 1
-	}), 0)
-	if hwnd == 0 {
-		hwnd, _, _ = getConsoleWindow.Call()
+	var wnd uintptr
+	enumWindows.Call(syscall.NewCallback(setupEnumCallback), uintptr(unsafe.Pointer(&wnd)))
+	if wnd == 0 {
+		wnd, _, _ = getConsoleWindow.Call()
 	}
-	if hwnd != 0 {
-		setForegroundWindow.Call(hwnd)
+	if wnd != 0 {
+		setForegroundWindow.Call(wnd)
 	}
 
 	runtime.LockOSThread()
@@ -140,6 +132,16 @@ func setup() context.CancelFunc {
 	}
 }
 
+func setupEnumCallback(wnd uintptr, lparam *uintptr) uintptr {
+	var pid uintptr
+	getWindowThreadProcessId.Call(wnd, uintptr(unsafe.Pointer(&pid)))
+	if int(pid) == os.Getpid() {
+		*lparam = wnd
+		return 0 // stop enumeration
+	}
+	return 1 // continue enumeration
+}
+
 func commDlgError() error {
 	s, _, _ := commDlgExtendedError.Call()
 	if s == 0 {