nautechsystems/nautilus_trader · error

Failed to register Betfair race fatal task: {e}

Error message

Failed to register Betfair race fatal task: {e}

What it means

Registering the race stream's fatal-error monitoring task failed; the underlying error `{e}` is re-wrapped. This task watches the race stream for fatal conditions and triggers reconnection/shutdown; without it, a dead race stream would go undetected, so connect aborts.

Source

Thrown at crates/adapters/betfair/src/data.rs:883

                            .push(BetfairStreamShutdown::Auxiliary(Arc::clone(&race_client)));

                        let race_socket_control = self.race_socket_control.as_ref().map(Arc::clone);

                        self.session_tasks
                        .spawn(async move {
                            if race_fatal_rx.recv().await.is_some() {
                                log::error!(
                                    "Betfair race stream permanently disabled due to fatal error"
                                );
                                race_client.close().await;

                                if let Some(control) = race_socket_control {
                                    control.deregister();
                                }
                            }
                        })
                        .map_err(|e| {
                            anyhow::anyhow!("Failed to register Betfair race fatal task: {e}")
                        })?;

                        log::debug!("Betfair race stream connected");
                    }
                    Err(e) => {
                        log::warn!("Betfair race stream connect failed: {e}");

                        if let Some(control) = &self.race_socket_control {
                            control.deregister();
                        }
                        self.race_stream_client = None;
                    }
                }
            }

            if self.config.subscribe_cricket_data {
                let cricket_config = BetfairStreamConfig {
                    host: BETFAIR_RACE_STREAM_HOST.to_string(),

View on GitHub (pinned to 18893faf8b)

Solutions

  1. Read the inner `{e}` for the exact registration failure (likely TaskGroup spawn error)
  2. Ensure connect is not racing disconnect/shutdown on the same client
  3. Retry connect so the race stream and its fatal watcher are registered in the same generation
  4. Note: race stream connect failure itself is only a warning; only the fatal-task registration aborts — check whether the race stream endpoint actually connected
Defensive patterns

Strategy: try-catch

Validate before calling

// ensure no shutdown in progress before connect
if client.is_shutting_down() { return Err(anyhow::anyhow!("connect during shutdown")); }

Try / catch

match client.connect().await {
    Err(e) if e.to_string().contains("Failed to register Betfair race fatal task") => {
        log::error!("race fatal watcher not registered: {e:#}");
        // retry connect; ensure disconnect() isn't running concurrently
    }
    other => other,
}

Prevention

When it happens

Trigger: connect() -> after spawning the race stream task, .map_err wraps the registration (spawn onto a task group / stream shutdown registry) error. Typically occurs when the target TaskGroup is not open (shutdown in progress) or the spawn fails because the group was closed concurrently.

Common situations: Connect racing a disconnect that closed the task group; reconnect loops where the group generation ended before registration; internal spawn failure.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/51667dc0fdd9ef15. Report an issue: GitHub.