let mut workers: Vec<std::thread::JoinHandle<()>> = Vec::new();

        let mut workers: Vec<std::thread::JoinHandle<_>> = Vec::new();

            workers.push(std::thread::spawn(move || loop {
                let (w, stop) = {
                    let mut work = work.lock().unwrap();
                    (work.t.pop_front(), work.stop)
                };
                if let Some((item, vertex, rec, new_papa)) = w {
                    // This parent has changed.
                    info!("record existing file {:?} on thread {:?}", item, t);
                    rec.lock()
                        .unwrap()
                        .record_existing_file(
                            txn.clone(),
                            diff_algorithm,
                            channel.clone(),
                            working_copy.clone(),
                            &changes,
                            &item,
                            new_papa,
                            vertex,
                        )
                        .unwrap();
                } else if stop {
                    info!("stop {:?}", t);
                    break;
                } else {
                    info!("yield {:?}", t);
                    std::thread::park_timeout(std::time::Duration::from_secs(1));

            workers.push(std::thread::spawn(move || {
                loop {
                    let (w, stop) = {
                        let mut work = work.lock().unwrap();
                        (work.t.pop_front(), work.stop)
                    };
                    if let Some((item, vertex, rec, new_papa)) = w {
                        // This parent has changed.
                        info!("record existing file {:?} on thread {:?}", item, t);
                        rec.lock()
                            .unwrap()
                            .record_existing_file(
                                txn.clone(),
                                diff_algorithm,
                                channel.clone(),
                                working_copy.clone(),
                                &changes,
                                &item,
                                new_papa,
                                vertex,
                            )?;
                    } else if stop {
                        info!("stop {:?}", t);
                        break;
                    } else {
                        info!("yield {:?}", t);
                        std::thread::park_timeout(std::time::Duration::from_secs(1));
                    }

                Ok::<_, RecordError<C::Error, W::Error, T::GraphError>>(())

                    )
                    .unwrap();

                    )?;

            t.join().unwrap()

            match t.join() {
                Ok(x) => x?,
                Err(e) => {
                    warn!("Thread error {:?}", e);
                }
            }