Background residency

This example combines background residency with single-instance activation. Closing the last window keeps the application alive, so a later launch can reach the existing instance instead of starting another runtime.

57_background_residency · Source files: main.mbt

Behavior

KeepRunning retains the process. A second launch delivers Reopen; the handler recreates main only when it is absent.

Implementation

Excerpt from the entry point; use the source link above for the complete context.

async fn main {
  @proton.html("Background Residency", page, width=760, height=480)
  ..identifier("com.example.proton.background-residency")
  ..single_instance()
  ..last_window_closed_policy(@proton.LastWindowClosedPolicy::KeepRunning)
  ..on_launch_input(async fn(context, input) noraise {
    if input is Reopen && context.windows().find("main") is None {
      ignore(context.windows().open("main")) catch {
        error => println("failed to reopen main window: " + error.to_string())
      }
    }
  })
  .run_or_abort()
}

KeepRunning changes last-window behavior, while single_instance routes later launches into the existing process. On Reopen, the callback first checks whether main exists and opens a new instance only when absent. Closing a window and quitting the application are deliberately different operations.

A real background application needs an accessible explicit Quit action, such as a tray command. Stopping the development process demonstrates forced termination, not successful lifecycle cleanup. Reopen obtains a fresh window instance; do not keep the previous handle.

Run

After completing source checkout and runtime setup, run from the repository root:

moon -C examples run 57_background_residency --target native

Limits and interpretation

Closing the window intentionally does not quit. End the process using the platform Quit action or stop the development command. This differs from the default last-window policy.