WorkerThread 主循环

pub(super) struct WorkerThread {
    /// the "worker" half of our local deque
    worker: Worker<JobRef>,

    /// the "stealer" half of the worker's broadcast deque
    stealer: Stealer<JobRef>,

    /// local queue used for `spawn_fifo` indirection
    fifo: JobFifo,

    index: usize,

    /// A weak random number generator.
    rng: XorShift64Star,

    registry: Arc<Registry>,
}

// This is a bit sketchy, but basically: the WorkerThread is
// allocated on the stack of the worker on entry and stored into this
// thread-local variable. So it will remain valid at least until the
// worker is fully unwound. Using an unsafe pointer avoids the need
// for a RefCell<T> etc.
thread_local! {
    static WORKER_THREAD_STATE: Cell<*const WorkerThread> = const { Cell::new(ptr::null()) };
}

unsafe fn main_loop(thread: ThreadBuilder) {
    let worker_thread = &WorkerThread::from(thread);
    WorkerThread::set_current(worker_thread);
    let registry = &*worker_thread.registry;
    let index = worker_thread.index;

    // let registry know we are ready to do work
    Latch::set(&registry.thread_infos[index].primed);

    // Worker threads should not panic. If they do, just abort, as the
    // internal state of the thread pool is corrupted. Note that if
    // **user code** panics, we should catch that and redirect.
    let abort_guard = unwind::AbortIfPanic;

    // Inform a user callback that we started a thread.
    if let Some(ref handler) = registry.start_handler {
        registry.catch_unwind(|| handler(index));
    }

    worker_thread.wait_until_out_of_work();

    // Normal termination, do not abort.
    mem::forget(abort_guard);

    // Inform a user callback that we exited a thread.
    if let Some(ref handler) = registry.exit_handler {
        registry.catch_unwind(|| handler(index));
        // We're already exiting the thread, there's nothing else to do.
    }
}

    fn find_work(&self) -> Option<JobRef> {
        // Try to find some work to do. We give preference first
        // to things in our local deque, then in other workers
        // deques, and finally to injected jobs from the
        // outside. The idea is to finish what we started before
        // we take on something new.
        self.take_local_job()
            .or_else(|| self.steal())
            .or_else(|| self.registry.pop_injected_job())
    }

    #[inline]
    pub(super) unsafe fn wait_until<L: AsCoreLatch + ?Sized>(&self, latch: &L) {
        let latch = latch.as_core_latch();
        if !latch.probe() {
            self.wait_until_cold(latch);
        }
    }

    #[cold]
    unsafe fn wait_until_cold(&self, latch: &CoreLatch) {
        // the code below should swallow all panics and hence never
        // unwind; but if something does wrong, we want to abort,
        // because otherwise other code in rayon may assume that the
        // latch has been signaled, and that can lead to random memory
        // accesses, which would be *very bad*
        let abort_guard = unwind::AbortIfPanic;

        'outer: while !latch.probe() {
            // Check for local work *before* we start marking ourself idle,
            // especially to avoid modifying shared sleep state.
            if let Some(job) = self.take_local_job() {
                self.execute(job);
                continue;
            }

            let mut idle_state = self.registry.sleep.start_looking(self.index);
            while !latch.probe() {
                if let Some(job) = self.find_work() {
                    self.registry.sleep.work_found();
                    self.execute(job);
                    // The job might have injected local work, so go back to the outer loop.
                    continue 'outer;
                } else {
                    self.registry
                        .sleep
                        .no_work_found(&mut idle_state, latch, || self.has_injected_job())
                }
            }

            // If we were sleepy, we are not anymore. We "found work" --
            // whatever the surrounding thread was doing before it had to wait.
            self.registry.sleep.work_found();
            break;
        }

        mem::forget(abort_guard); // successful execution, do not abort
    }