zed-industries/zed · error

failed to spawn dedicated thread

Error message

failed to spawn dedicated thread

What it means

Raised in spawn_dedicated_os_thread(): std::thread::Builder::spawn for the dedicated scheduler thread failed (thread creation error, e.g. resource limits), so the dedicated executor session cannot start.

Source

Thrown at crates/scheduler/src/scheduler.rs:212

        // lives inside a spawned task or a user-held executor clone. The
        // recv loop exits once all of those are gone.
        drop(executor);

        while let Ok(runnable) = runnable_receiver.recv() {
            runnable.run();
        }
    };
    spawn_dedicated_os_thread(session_id, thread_body);
    task
}

fn spawn_dedicated_os_thread(session_id: SessionId, thread_body: impl FnOnce() + Send + 'static) {
    let thread_name = format!("spawn_dedicated session {:?}", session_id);
    #[cfg(not(target_family = "wasm"))]
    std::thread::Builder::new()
        .name(thread_name)
        .spawn(thread_body)
        .expect("failed to spawn dedicated thread");
    #[cfg(all(target_family = "wasm", feature = "wasm-threads"))]
    wasm_thread::Builder::new()
        .name(thread_name)
        .spawn(thread_body)
        .expect("failed to spawn dedicated thread");
    #[cfg(all(target_family = "wasm", not(feature = "wasm-threads")))]
    {
        let _ = (thread_name, thread_body);
        panic!("spawn_dedicated on wasm requires the scheduler crate's `wasm-threads` feature");
    }
}

#[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
pub struct SessionId(u16);

impl SessionId {
    pub fn new(id: u16) -> Self {
        SessionId(id)

View on GitHub (pinned to f4178619ac)

Solutions

1. Reduce concurrent thread usage in the process
2. Check ulimit -u / pthread limits on the host
3. Retry after load subsides or fall back to a shared thread pool

When it happens

Trigger: Thrown at crates/scheduler/src/scheduler.rs:212 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of zed-industries/zed@f4178619ac (2026-08-20). Data as JSON: /api/errors/293472c391cbe859. Report an issue: GitHub.