fix: Flex with multiple slices opened was always showing slice A s-meter.

singleinstance_windows.go

@@ -0,0 +1,64 @@
+//go:build windows
+
+package main
+
+import (
+	"errors"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+// singleInstanceName is a per-session named mutex. The Windows kernel releases
+// it automatically when the owning process dies (even on a crash), so a
+// lingering/zombie OpsLog can't permanently block future launches — killing it
+// frees the name at once. Session-local (no "Global\\") = one instance per
+// logged-in desktop, which is what we want.
+const singleInstanceName = "OpsLog-SingleInstance-Mutex"
+
+// acquireSingleInstance creates the named mutex. Returns ok=false when another
+// OpsLog already holds it (this instance should exit); on the way out it brings
+// the existing window to the front so a double-click just refocuses OpsLog
+// instead of spawning a duplicate that fights over the CAT / antenna.
+//
+// The mutex handle is deliberately never closed — it must live for the whole
+// process lifetime; the OS reclaims it on exit.
+func acquireSingleInstance() (ok bool) {
+	namePtr, err := windows.UTF16PtrFromString(singleInstanceName)
+	if err != nil {
+		return true // never block launch on an unexpected error
+	}
+	kernel32 := windows.NewLazySystemDLL("kernel32.dll")
+	createMutex := kernel32.NewProc("CreateMutexW")
+	// CreateMutexW(lpSecurityAttributes=NULL, bInitialOwner=FALSE, lpName)
+	h, _, callErr := createMutex.Call(0, 0, uintptr(unsafe.Pointer(namePtr)))
+	if h == 0 {
+		return true // couldn't create the mutex → don't block the app
+	}
+	if errors.Is(callErr, windows.ERROR_ALREADY_EXISTS) {
+		focusExistingWindow()
+		return false
+	}
+	return true
+}
+
+// focusExistingWindow finds the running OpsLog window by its title and restores
+// + foregrounds it. Best-effort; failures are silently ignored.
+func focusExistingWindow() {
+	user32 := windows.NewLazySystemDLL("user32.dll")
+	findWindow := user32.NewProc("FindWindowW")
+	setForeground := user32.NewProc("SetForegroundWindow")
+	showWindow := user32.NewProc("ShowWindow")
+
+	title, err := windows.UTF16PtrFromString("OpsLog")
+	if err != nil {
+		return
+	}
+	hwnd, _, _ := findWindow.Call(0, uintptr(unsafe.Pointer(title)))
+	if hwnd == 0 {
+		return
+	}
+	const swRestore = 9 // SW_RESTORE — un-minimise if needed
+	showWindow.Call(hwnd, swRestore)
+	setForeground.Call(hwnd)
+}