zed-industries/zed · error

main thread message channel, extension {name} (id {id})

Error message

main thread message channel, extension {name} (id {id})

What it means

The return half of the extension main-thread handshake: after posting work, the extension awaits a oneshot receiver for the result. If the main thread dropped the closure without sending a reply (the app quit mid-call), the oneshot sender is destroyed, `await` errors, and the extension panics with the extension name and id.

Source

Thrown at crates/extension_host/src/wasm_host.rs:968

        let (return_tx, return_rx) = oneshot::channel();
        self.host
            .main_thread_message_tx
            .clone()
            .unbounded_send(Box::new(move |cx| {
                async {
                    let result = f(cx).await;
                    return_tx.send(result).ok();
                }
                .boxed_local()
            }))
            .unwrap_or_else(|_| {
                panic!(
                    "main thread message channel should not be closed yet, extension {} (id {})",
                    self.manifest.name, self.manifest.id,
                )
            });
        let name = self.manifest.name.clone();
        let id = self.manifest.id.clone();
        async move {
            return_rx.await.unwrap_or_else(|_| {
                panic!("main thread message channel, extension {name} (id {id})")
            })
        }
    }

    fn work_dir(&self) -> PathBuf {
        self.host.work_dir.join(self.manifest.id.as_ref())
    }

    fn extension_error(&self, message: String) -> anyhow::Error {
        anyhow!(
            "from extension \"{}\" version {}: {}",
            self.manifest.name,
            self.manifest.version,
            message
        )

View on GitHub (pinned to 5a9b9558db)

Solutions

1. Update Zed — the host should stop dispatching extension work before dropping the main-thread channel; such races are fixed upstream
2. Extension authors: make deactivate cancel in-flight tasks so nothing is left awaiting main-thread replies during quit
3. Report with the extension name/id from the message and the exact quit sequence that triggers it

When it happens

Trigger: App shutdown occurring while an extension is awaiting the result of a main-thread API call — the posted closure never runs, so no result is ever sent.

Common situations: Quitting Zed while an extension has an in-flight command or API request; races during rapid window close; extension tasks that outlive deactivate.

Related errors

• main thread message channel should not be closed yet, extens
• blocking sender returned without value
• row out of range
• invalid display row {}
• anchor's path was never added to multibuffer

AI-assisted analysis of zed-industries/zed@5a9b9558db (2026-08-20). Data as JSON: /api/errors/85cd3478252cd842. Report an issue: GitHub.