nautechsystems/nautilus_trader · error

Failed to start AX data session generation: {e}

Error message

Failed to start AX data session generation: {e}

What it means

On connect, if the client detects stale state (existing session/pending tasks or funding-rate cancellations), it tears down the partial connection and starts a fresh session-task generation. If start_generation fails, connect aborts with "Failed to start AX data session generation". This means the task group could not be reset for a clean session.

Source

Thrown at crates/adapters/architect_ax/src/data.rs:457

            && !self.cancellation_token.is_cancelled()
            && self.pending_tasks.is_open()
            && self.session_tasks.is_open()
        {
            log::debug!("Already connected {}", self.client_id);
            return Ok(());
        }

        log::info!("Connecting {}", self.client_id);

        if self.cancellation_token.is_cancelled()
            || !self.pending_tasks.is_open()
            || !self.session_tasks.is_open()
            || !self.funding_rate_cancellations.is_empty()
        {
            self.teardown_partial_connect().await?;
            self.session_tasks
                .start_generation()
                .map_err(|e| anyhow::anyhow!("Failed to start AX data session generation: {e}"))?;
            self.pending_tasks
                .start_generation()
                .map_err(|e| anyhow::anyhow!("Failed to start AX data task generation: {e}"))?;
            self.cancellation_token = CancellationToken::new();
        }
        let cancellation_token = self.cancellation_token.clone();
        let ws_client = self.ws_client.clone();
        let setup_guard =
            TaskGroupGuard::new(&[&self.session_tasks, &self.pending_tasks], move || {
                cancellation_token.cancel();
                ws_client.begin_shutdown();
            });

        let credential = if self.config.has_api_credentials() {
            let credential = Credential::resolve(
                self.config.api_key.clone().map(|value| value.into_inner()),
                self.config
                    .api_secret

View on GitHub (pinned to 18893faf8b)

Solutions

1. Ensure disconnect/teardown_partial_connect completed before reconnecting; await it fully
2. Avoid calling connect concurrently from multiple tasks (serialize with a lock/flag)
3. Retry connect after inspecting task group state; recreate the client if state is corrupted
4. Check the inner error text for the specific start_generation failure

Example fix

// before
client.connect().await?;
// after
drop(client); // or ensure previous disconnect completed
let client = AXDataClient::new(...); // fresh client on repeated start_generation failures
client.connect().await?;

// Rust
// single-owner pattern: never call connect concurrently
// if reconnecting, await previous disconnect() fully first

// Rust
loop {
    match client.connect().await {
        Ok(()) => break,
        Err(e) if e.to_string().contains("session generation") && retries < 3 => {
            client.disconnect().await.ok();
            retries += 1;
        }
        Err(e) => return Err(e),
    }
}

When it happens

Trigger: Calling connect when prior session_tasks are still open/registered and the session task group's start_generation returns an error (e.g. generation already in progress or group in an inconsistent state).

Common situations: Reconnecting after a previous disconnect that left tasks behind; concurrent connect calls racing on the same client; a previous teardown that did not fully complete.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• Failed to start AX data task generation: {e}
• std::mem::take(&mut self.shutdown_errors).join("; ")
• std::mem::take(&mut self.shutdown_errors).join("; ")
• Blockchain execution client is not connected
• WebSocket output receiver not available

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/9c9c5ff8afaf8530. Report an issue: GitHub.