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82 lines
3.7 KiB
Plaintext
82 lines
3.7 KiB
Plaintext
# Single Instance Lock
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Single instance lock is a mechanism that allows you to prevent multiple instances of your app from running at the same time.
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It is useful for apps that are designed to open files from the command line or from the OS file explorer.
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## Important
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Single Instance Lock does not implement a secure communications protocol between instances. When using single instance lock,
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your app should treat any data passed to it from second instance callback as untrusted.
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You should verify that args that you receive are valid and don't contain any malicious data.
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## How it works
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Windows: Single instance lock is implemented using a named mutex. The mutex name is generated from the unique id that you provide. Data is passed to the first instance via a shared window using [SendMessage](https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-sendmessage)
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macOS: Single instance lock is implemented using a named mutex. The mutex name is generated from the unique id that you provide. Data is passed to the first instance via [NSDistributedNotificationCenter](https://developer.apple.com/documentation/foundation/nsdistributednotificationcenter)
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Linux: Single instance lock is implemented using [dbus](https://www.freedesktop.org/wiki/Software/dbus/). The dbus name is generated from the unique id that you provide. Data is passed to the first instance via [dbus](https://www.freedesktop.org/wiki/Software/dbus/)
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## Usage
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When creating your app, you can enable single instance lock by passing a `SingleInstanceLock` struct to the `App` struct.
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Use the `UniqueId` field to specify a unique id for your app.
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This id is used to generate the mutex name on Windows and macOS and the dbus name on Linux. Use a UUID to ensure that the id is unique.
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The `OnSecondInstanceLaunch` field is used to specify a callback that is called when a second instance of your app is launched.
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The callback receives a `SecondInstanceData` struct that contains the command line arguments passed to the second instance and the working directory of the second instance.
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Note that OnSecondInstanceLaunch don't trigger windows focus.
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You need to call `runtime.WindowUnminimise` and `runtime.Show` to bring your app to the front.
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Note that on linux systems window managers may prevent your app from being brought to the front to avoid stealing focus.
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```go title="main.go"
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var wailsContext *context.Context
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// NewApp creates a new App application struct
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func NewApp() *App {
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return &App{}
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}
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// startup is called when the app starts. The context is saved
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// so we can call the runtime methods
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func (a *App) startup(ctx context.Context) {
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wailsContext = &ctx
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}
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func (a *App) onSecondInstanceLaunch(secondInstanceData options.SecondInstanceData) {
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secondInstanceArgs = secondInstanceData.Args
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println("user opened second instance", strings.Join(secondInstanceData.Args, ","))
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println("user opened second from", secondInstanceData.WorkingDirectory)
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runtime.WindowUnminimise(*wailsContext)
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runtime.Show(*wailsContext)
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go runtime.EventsEmit(*wailsContext, "launchArgs", secondInstanceArgs)
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}
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func main() {
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// Create an instance of the app structure
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app := NewApp()
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// Create application with options
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err := wails.Run(&options.App{
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Title: "wails-open-file",
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Width: 1024,
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Height: 768,
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AssetServer: &assetserver.Options{
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Assets: assets,
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},
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BackgroundColour: &options.RGBA{R: 27, G: 38, B: 54, A: 1},
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OnStartup: app.startup,
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SingleInstanceLock: &options.SingleInstanceLock{
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UniqueId: "e3984e08-28dc-4e3d-b70a-45e961589cdc",
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OnSecondInstanceLaunch: app.onSecondInstanceLaunch,
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},
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Bind: []interface{}{
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app,
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},
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})
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if err != nil {
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println("Error:", err.Error())
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}
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}
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```
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