Function make_callback_done_handler

dash/backends/ws.py:326–391

Create a done callback handler for executor futures. This factory creates a callback that sends the result back through the WebSocket when an executor future completes. Args: outbound_queue: janus.Queue for sending responses pending_callbacks: Dict tracking pending call

(
    outbound_queue: janus.Queue[str],
    pending_callbacks: Dict[str, concurrent.futures.Future],
    request_id: str,
    renderer_id: str,
    shutdown_event: threading.Event,
)

def make_callback_done_handler(
    outbound_queue: janus.Queue[str],
    pending_callbacks: Dict[str, concurrent.futures.Future],
    request_id: str,
    renderer_id: str,
    shutdown_event: threading.Event,
) -> Callable[[concurrent.futures.Future], None]:
    """Create a done callback handler for executor futures.

    This factory creates a callback that sends the result back through
    the WebSocket when an executor future completes.

    Args:
        outbound_queue: janus.Queue for sending responses
        pending_callbacks: Dict tracking pending callbacks for cleanup
        request_id: The request ID for the callback response
        renderer_id: The renderer ID for routing the response
        shutdown_event: Event signaling the websocket connection has closed.

    Returns:
        A callback function suitable for Future.add_done_callback()
    """

    def on_done(f: concurrent.futures.Future) -> None:
        try:
            if shutdown_event.is_set():
                return
            result = f.result()
            outbound_queue.sync_q.put_nowait(
                cast(
                    str,
                    to_json(
                        {
                            "type": "callback_response",
                            "rendererId": renderer_id,
                            "requestId": request_id,
                            "payload": result,
                        }
                    ),
                )
            )
        except Exception as e:  # pylint: disable=broad-exception-caught
            if shutdown_event.is_set():
                return
            outbound_queue.sync_q.put_nowait(
                cast(
                    str,
                    to_json(
                        {
                            "type": "callback_response",
                            "rendererId": renderer_id,
                            "requestId": request_id,
                            "payload": {
                                "status": "error",
                                "message": str(e),
                            },
                        }
                    ),