What causes "Failed to start Databento task generation: {e}" in nautechsystems/nautilus_trader?

Confirm the client runs within a tokio runtime (use #[tokio::main] or a runtime handle)

nautechsystems/nautilus_trader · error · anyhow::Error

Failed to start Databento task generation: {e}

Error message

Failed to start Databento task generation: {e}

What it means

After terminating prior tasks, `connect` starts a new task generation via `task_handles.start_generation`. If spawning/starting the generation fails, connect aborts with this error. This means the client cannot establish its background Databento tasks.

Source

Thrown at crates/adapters/databento/src/data.rs:503

        Ok(())
    }

    fn dispose(&mut self) -> anyhow::Result<()> {
        log::debug!("Disposing");
        self.stop()
    }

    async fn connect(&mut self) -> anyhow::Result<()> {
        log::debug!("Connecting...");

        if !self.task_handles.is_open() {
            self.task_handles
                .finish_shutdown(Duration::from_secs(1), Duration::from_secs(2))
                .await
                .map_err(|e| anyhow::anyhow!("Failed to terminate Databento tasks: {e}"))?;
            self.task_handles
                .start_generation()
                .map_err(|e| anyhow::anyhow!("Failed to start Databento task generation: {e}"))?;
            self.cancellation_token = self.task_handles.cancellation_token();
        }

        self.is_connected.store(true, Ordering::Relaxed);

        log::info!("Connected");
        Ok(())
    }

    async fn disconnect(&mut self) -> anyhow::Result<()> {
        log::debug!("Disconnecting...");

        self.send_close_to_active_feeds();
        self.clear_feed_channels();
        self.task_handles.begin_shutdown();

        let tasks_result = self
            .task_handles

View on GitHub (pinned to 18893faf8b)

Solutions

Confirm the client runs within a tokio runtime (use #[tokio::main] or a runtime handle)
Retry connect(); if generation state is stuck, drop and recreate the client
Check for previous shutdown failures (companion 'Failed to terminate Databento tasks' error) and fix that root cause first
Inspect logs from TaskHandleTracker for the underlying spawn error

Example fix

// before
let client = DatabentoDataClient::new(...);
client.connect().await?; // fails outside runtime
// after
#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let client = DatabentoDataClient::new(...);
    client.connect().await
}

Defensive patterns

Strategy: retry

Validate before calling

// ensure a tokio runtime exists before client use
let runtime = tokio::runtime::Handle::try_current()
    .map_err(|_| anyhow::anyhow!("DatabentoDataClient requires a tokio runtime"))?;

Try / catch

match client.connect().await {
    Err(e) if e.to_string().contains("Failed to start Databento task generation") => {
        eprintln!("dropping and recreating client after generation failure: {e}");
        let client = rebuild_client()?;
        client.connect().await?;
    }
    other => other?,
}

Prevention

Run the client inside an active tokio runtime
Check for companion shutdown failures which leave generation state inconsistent
Recreate the client rather than retrying connect() when generation start keeps failing

When it happens

Trigger: Calling connect() when `start_generation` fails — e.g. tokio runtime issues, spawn failures, or internal generation bookkeeping errors in TaskHandleTracker.

Common situations: Running the client outside a tokio runtime context, resource exhaustion preventing task spawn, or a corrupted/overlapping generation state after repeated reconnects.

Related errors

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/30e1e2d7f869984d. Report an issue: GitHub.