Function _handle_rest_background_callback

dash/_callback.py:522–577

(
    output_value,
    callback_manager,
    response,
    error_handler,
    callback_ctx,
    multi,
    has_update=False,
    cache_key=None,
    job_id=None,
)

def _handle_rest_background_callback(
    output_value,
    callback_manager,
    response,
    error_handler,
    callback_ctx,
    multi,
    has_update=False,
    cache_key=None,
    job_id=None,
):
    if cache_key is None or job_id is None:
        adapter = get_app().backend.request_adapter()
        cache_key = cache_key or (adapter.args.get("cacheKey") if adapter else None)
        job_id = job_id or (adapter.args.get("job") if adapter else None)
    # Must get job_running after get_result since get_results terminates it.
    job_running = callback_manager.job_running(job_id)
    if not job_running and output_value is callback_manager.UNDEFINED:
        # Job canceled -> no output to close the loop.
        output_value = NoUpdate()

    elif isinstance(output_value, dict) and "background_callback_error" in output_value:
        error = output_value.get("background_callback_error", {})
        exc = BackgroundCallbackError(
            f"An error occurred inside a background callback: {error['msg']}\n{error['tb']}"
        )
        if error_handler:
            output_value = error_handler(exc)

            if output_value is None:
                output_value = NoUpdate()
            # set_props from the error handler uses the original ctx
            # instead of manager.get_updated_props since it runs in the
            # request process.
            has_update = (
                _set_side_update(callback_ctx, response) or output_value is not None
            )
        else:
            raise exc

    if job_running and output_value is not callback_manager.UNDEFINED:
        # cached results.
        callback_manager.terminate_job(job_id)

    if multi and isinstance(output_value, (list, tuple)):
        output_value = [
            NoUpdate() if NoUpdate.is_no_update(r) else r for r in output_value
        ]
    updated_props = callback_manager.get_updated_props(cache_key)
    if len(updated_props) > 0:
        response["sideUpdate"] = updated_props
        has_update = True

    if output_value is callback_manager.UNDEFINED:
        return to_json(response), has_update, True
    return output_value, has_update, False