What causes "unable to run main eventloop" in espanso/espanso?

Restart espanso after the display session is stable again (`espanso restart`).

unable to run main eventloop

Error message

unable to run main eventloop

What it means

eventloop.run() starts the main UI event loop, dispatching every UI event to the engine through a channel; this expect panics if run returns Err. Once this fails the worker cannot process events at all and must terminate.

Source

Thrown at espanso/src/cli/worker/mod.rs:168

    // terminate the worker if the daemon terminates
    // This is needed to avoid "dangling" worker processes
    // if the daemon crashes or is forcefully terminated.
    if cli_args.is_present("monitor-daemon") {
        daemon_monitor::initialize_and_spawn(&paths.runtime, engine_exit_notify)
            .expect("unable to initialize daemon monitor thread");
    }

    secure_input::initialize_and_spawn(engine_secure_input_sender)
        .expect("unable to initialize secure input watcher");

    eventloop
        .run(Box::new(move |event| {
            if let Err(error) = engine_ui_event_sender.send(event) {
                error!("unable to send UIEvent to engine: {error}");
                panic!("broken UI->Engine channel");
            }
        }))
        .expect("unable to run main eventloop");

    info!("waiting for engine exit mode...");
    match engine_handle.join() {
        Ok(mode) => match mode {
            ExitMode::Exit => {
                info!("exiting worker process...");
                WORKER_SUCCESS
            }
            ExitMode::ExitAllProcesses => {
                info!("exiting worker process and daemon...");
                WORKER_EXIT_ALL_PROCESSES
            }
            ExitMode::RestartWorker => {
                info!("exiting worker (to be restarted)");
                WORKER_RESTART
            }
        },
        Err(err) => {

View on GitHub (pinned to e6c3736675)

Solutions

Restart espanso after the display session is stable again (`espanso restart`).
Check whether the engine thread died first (broken UI->Engine channel panic) and fix the root engine failure seen earlier in logs.
Avoid restarting the display manager/compositor while espanso runs; stop espanso first.
Inspect platform logs for X11/Wayland disconnection errors and fix the session stability issue.

Defensive patterns

Strategy: try-catch

Try / catch

if let Err(err) = eventloop.run(Box::new(move |event| { ... })) {
    error!("main eventloop terminated: {err}");
    // trigger supervised restart via the daemon
    std::process::exit(1);
}

Prevention

Stop espanso before logging out or restarting the display server.
Monitor the engine thread health; a dead engine causes the UI->Engine channel panic inside the callback.
Run the worker under daemon supervision so a fatal eventloop failure triggers a clean restart.

When it happens

Trigger: The platform event loop's run() returns an error — display connection lost mid-run (X server terminated, Wayland compositor restart), the UI subsystem hit a fatal error while pumping events, or the callback panicked (broken UI->Engine channel) propagating failure.

Common situations: Logging out or restarting the display server while espanso runs, X11/Wayland session crashes, desktop environment switching, or the engine thread having exited causing the send in the callback to fail and panic.

Related errors

AI-assisted analysis of espanso/espanso@e6c3736675 (2026-09-06). Data as JSON: /api/errors/f2c042e379aa2e45. Report an issue: GitHub.