What causes "Failed to send order pending cancel event: {e}" in nautechsystems/nautilus_trader?

Keep the execution event loop alive until the adapter is disconnected and all in-flight cancels settle.

nautechsystems/nautilus_trader · error · anyhow::Error

Failed to send order pending cancel event: {e}

Error message

Failed to send order pending cancel event: {e}

What it means

When a pending-cancel state is emitted, the adapter sends an `OrderEventAny::PendingCancel` event over the unbounded mpsc `exec_sender`. Failure means the receiver has been dropped, so the pending-cancel transition cannot be recorded and the error is wrapped and propagated out of the helper.

Source

Thrown at crates/adapters/interactive_brokers/src/execution/core.rs:2429

        let (trader_id, strategy_id) =
            Self::get_required_order_actor_ids(order_id, trader_id_map, strategy_id_map)?;

        let event = OrderPendingCancel::new(
            trader_id,
            strategy_id,
            instrument_id,
            client_order_id,
            Some(account_id),
            UUID4::new(),
            ts_init,
            ts_init,
            false,
            Some(venue_order_id),
        );

        exec_sender
            .send(ExecutionEvent::Order(OrderEventAny::PendingCancel(event)))
            .map_err(|e| anyhow::anyhow!("Failed to send order pending cancel event: {e}"))?;

        Ok(())
    }
}

View on GitHub (pinned to 18893faf8b)

Solutions

Keep the execution event loop alive until the adapter is disconnected and all in-flight cancels settle.
Confirm the exec channel receiver is correctly registered before issuing cancels.
Treat the failure as non-fatal at teardown by logging a warning instead of aborting.

Example fix

// before
exec_sender
    .send(ExecutionEvent::Order(OrderEventAny::PendingCancel(event)))
    .map_err(|e| anyhow::anyhow!("Failed to send order pending cancel event: {e}"))?;
// after
if let Err(e) = exec_sender.send(ExecutionEvent::Order(OrderEventAny::PendingCancel(event))) {
    log::warn!("pending cancel event dropped (receiver closed): {e}");
}

Defensive patterns

Strategy: try-catch

Try / catch

if let Err(e) = client.cancel_order(&cmd).await {
    if e.to_string().contains("Failed to send order pending cancel event") {
        log::warn!("pending cancel event lost (receiver closed): {e}");
    } else {
        return Err(e);
    }
}

Prevention

Keep the execution event loop running until all in-flight cancels reach a terminal state.
Disconnect the adapter only after the engine and its event receiver are still alive to consume final events.
Monitor shutdown logs for late PendingCancel/Denied events to tune teardown ordering.

When it happens

Trigger: The adapter emits PendingCancel (e.g. a cancel request was accepted/queued at IB) while the execution event receiver is closed — during node shutdown or if the channel wiring was torn down early.

Common situations: Cancel in flight at shutdown; IB acknowledging a cancel after the event loop stopped; tests/tools dropping the receiver before replaying queued events.

Related errors

AI-assisted analysis of nautechsystems/nautilus_trader@18893faf8b (2026-09-08). Data as JSON: /api/errors/13f59c02a297452e. Report an issue: GitHub.