flxzt/rnote · error · anyhow::Error

Channel closed before receiving a response from loader…

Error message

Channel closed before receiving a response from loader thread.

What it means

Thrown when the async channel (`rx_import`) used to receive the import result from the spawned PDF loader thread is dropped/closed before sending a value, so `rx_import.next().await` yields None. Indicates the loader task panicked, was cancelled, or the sender was dropped without emitting a result.

Solutions

Inspect the loader thread for panics/early returns — wrap the task body so a result (including error) is always sent through the channel.
Ensure `tx_import` is not dropped before the load completes (keep it alive via move into the task and send in all branches).
Retry the import; if reproducible, reproduce with the specific PDF and report/fix the parser panic.
Replace bare None handling with logging the loader-side error to diagnose which path dropped the sender.

Example fix

// before
match rx_import.next().await {
    Some(res) => res,
    None => Err(anyhow::anyhow!("Channel closed before receiving a response from loader thread.")),
}
// after
match rx_import.next().await {
    Some(res) => res,
    None => {
        tracing::error!("PDF loader thread ended without sending a result");
        Err(anyhow::anyhow!("Channel closed before receiving a response from loader thread."))
    }
}
// loader side: guarantee a send in every branch
gstd::panic::catch_unwind(...); tx_import.send(result).await.ok();

Defensive patterns

Strategy: try-catch

Try / catch

match rx_import.next().await {
    Some(res) => res,
    None => { tracing::error!("loader thread dropped sender"); Err(anyhow!("loader ended without result")) }
}

Prevention

Always send a Result through the channel in every loader branch
Catch panics in the loader task and convert them to Err results
Keep the sender alive for the whole task lifetime (move into closure)

When it happens

Trigger: In `dialog_import_pdf_w_prefs`, the spawned loader thread/task ends without sending on `tx_import` (panic inside PDF parsing, early return, or sender dropped), leaving `rx_import.next()` to return None.

Common situations: Loader thread panics on a malformed PDF; task aborted due to app shutdown or window close mid-import; a code change introduces a code path that drops the sender before `send`.

Related errors

AI-assisted analysis of flxzt/rnote@bbc5354502 (2026-09-08). Data as JSON: /api/errors/2c86b4526cf96d17. Report an issue: GitHub.

Appendix: source

Thrown at crates/rnote-ui/src/dialogs/import.rs:556

                            && let Err(e) = tx_import.unbounded_send(Err(e))
                        {
                            error!(
                                "Failed to load PDF, but failed to send signal through channel. Err: {e:?}"
                            );
                            return;
                        };

                        if let Err(e) = tx_import.unbounded_send(Ok(true)) {
                            error!(
                                "PDF file imported, but failed to send signal through channel. Err: {e:?}"
                            );
                        }
                    }
                ));

                match rx_import.next().await {
                    Some(res) => res,
                    None => Err(anyhow::anyhow!(
                        "Channel closed before receiving a response from loader thread."
                    )),
                }
            } else {
                Ok(false)
            }
        }
        None => Err(anyhow::anyhow!(
            "Channel closed before receiving a response from dialog."
        )),
    }
}

/// Imports the file as Xopp with an import dialog.
///
/// Returns true when the file was imported, else false.
pub(crate) async fn dialog_import_xopp_w_prefs(
    appwindow: &RnAppWindow,

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