Repository: tokio-rs/tokio
File: tokio/src/runtime/blocking/pool.rs (Rust)

Code before:

impl Drop for BlockingPool {
    fn drop(&mut self) {
        self.shutdown(None);
    }
}

impl fmt::Debug for BlockingPool {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt.debug_struct("BlockingPool").finish()
    }
}

// ===== impl Spawner =====

impl Spawner {
    pub(crate) fn spawn(&self, task: Task, rt: &Handle) -> Result<(), ()> {
        let shutdown_tx = {
            let mut shared = self.inner.shared.lock();

            if shared.shutdown {
                // Shutdown the task
                task.task.shutdown();

                // no need to even push this task; it would never get picked up
                return Err(());
            }

            shared.queue.push_back(task);

            if shared.num_idle == 0 {
                // No threads are able to process the task.

                if shared.num_th == self.inner.thread_cap {
                    // At max number of threads
                    None
                } else {
                    shared.num_th += 1;
                    assert!(shared.shutdown_tx.is_some());
                    shared.shutdown_tx.clone()
                }
            } else {
                // Notify an idle worker thread. The notification counter
                // is used to count the needed amount of notifications
                // exactly. Thread libraries may generate spurious
                // wakeups, this counter is used to keep us in a
                // consistent state.
                shared.num_idle -= 1;
                shared.num_notify += 1;
                self.inner.condvar.notify_one();
                None

Review comment (suggestion):
Perhaps include a comment here that it is ok to shut down a mandatory task here without running it because this only happens if the runtime has already started shutdown.

Code after:
}

impl Drop for BlockingPool {
    fn drop(&mut self) {
        self.shutdown(None);
    }
}

impl fmt::Debug for BlockingPool {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt.debug_struct("BlockingPool").finish()
    }
}

// ===== impl Spawner =====

impl Spawner {
    pub(crate) fn spawn(&self, task: Task, rt: &Handle) -> Result<(), ()> {
        let shutdown_tx = {
            let mut shared = self.inner.shared.lock();

            if shared.shutdown {
                // Shutdown the task: it's fine to shutdown this task (even if
                // mandatory) because it was scheduled after the shutdown of the
                // runtime began.
                task.task.shutdown();

                // no need to even push this task; it would never get picked up
                return Err(());
            }

            shared.queue.push_back(task);

            if shared.num_idle == 0 {
                // No threads are able to process the task.

                if shared.num_th == self.inner.thread_cap {
                    // At max number of threads
                    None
                } else {
                    shared.num_th += 1;
                    assert!(shared.shutdown_tx.is_some());
                    shared.shutdown_tx.clone()
                }
            } else {
                // Notify an idle worker thread. The notification counter
                // is used to count the needed amount of notifications
                // exactly. Thread libraries may generate spurious
                // wakeups, this counter is used to keep us in a
                // consistent state.
                shared.num_idle -= 1;