# Concurrency on GTK GTK apps run on GLib’s main loop, not `DispatchQueue.main`. ## The important rule Do **not** schedule GTK work with `Task { @MainActor in ... }` inside a running GTK application. Swift’s default main-actor executor uses the dispatch main queue, which GLib does not drain. Use `MainContext` instead. ## One-shot UI work ```swift MainContext.task { statusLabel.text = "Saved" } ``` ## Delayed work ```swift MainContext.task(after: .seconds(1)) { banner.revealed = false } ``` ## Async code that needs a main-loop hop ```swift let width = await MainContext.run { content.measure(orientation: .horizontal, forSize: -1).natural } ``` ## Repeating work ```swift MainContext.task(every: .milliseconds(250)) { spinner.spinning } ``` Return `true` to keep the task scheduled, `false` to stop it. ## Dialogs and async APIs Many wrappers expose both callback-based and `async` APIs. In GTK apps, run `async` dialog calls from `MainContext.task(priority:operation:)` so resumptions stay on the GLib-driven main loop. See [Working with Dialogs](/documentation/Adwaita/WorkingWithDialogs) for concrete file-dialog patterns.