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    use job::StackJob;
    use latch::{LatchProbe, SpinLatch};
    use log::Event::*;
    use registry::{self, WorkerThread};
    use std::any::Any;
    use unwind;

    use FnContext;

    #[cfg(test)]
    mod test;

    /// Takes two closures and *potentially* runs them in parallel. It
    /// returns a pair of the results from those closures.
    ///
    /// Conceptually, calling `join()` is similar to spawning two threads,
    /// one executing each of the two closures. However, the
    /// implementation is quite different and incurs very low
    /// overhead. The underlying technique is called "work stealing": the
    /// Rayon runtime uses a fixed pool of worker threads and attempts to
    /// only execute code in parallel when there are idle CPUs to handle
    /// it.
    ///
    /// When `join` is called from outside the thread pool, the calling
    /// thread will block while the closures execute in the pool.  When
    /// `join` is called within the pool, the calling thread still actively
    /// participates in the thread pool. It will begin by executing closure
    /// A (on the current thread). While it is doing that, it will advertise
    /// closure B as being available for other threads to execute. Once closure A
    /// has completed, the current thread will try to execute closure B;
    /// if however closure B has been stolen, then it will look for other work
    /// while waiting for the thief to fully execute closure B. (This is the
    /// typical work-stealing strategy).
    ///
    /// # Examples
    ///
    /// This example uses join to perform a quick-sort (note this is not a
    /// particularly optimized implementation: if you **actually** want to
    /// sort for real, you should prefer [the `par_sort` method] offered
    /// by Rayon).
    ///
    /// [the `par_sort` method]: ../rayon/slice/trait.ParallelSliceMut.html#method.par_sort
    ///
    /// ```rust
    /// # use rayon_core as rayon;
    /// let mut v = vec![5, 1, 8, 22, 0, 44];
    /// quick_sort(&mut v);
    /// assert_eq!(v, vec![0, 1, 5, 8, 22, 44]);
    ///
    /// fn quick_sort<T:PartialOrd+Send>(v: &mut [T]) {
    ///    if v.len() > 1 {
    ///        let mid = partition(v);
    ///        let (lo, hi) = v.split_at_mut(mid);
    ///        rayon::join(|| quick_sort(lo),
    ///                    || quick_sort(hi));
    ///    }
    /// }
    ///
    /// // Partition rearranges all items `<=` to the pivot
    /// // item (arbitrary selected to be the last item in the slice)
    /// // to the first half of the slice. It then returns the
    /// // "dividing point" where the pivot is placed.
    /// fn partition<T:PartialOrd+Send>(v: &mut [T]) -> usize {
    ///     let pivot = v.len() - 1;
    ///     let mut i = 0;
    ///     for j in 0..pivot {
    ///         if v[j] <= v[pivot] {
    ///             v.swap(i, j);
    ///             i += 1;
    ///         }
    ///     }
    ///     v.swap(i, pivot);
    ///     i
    /// }
    /// ```
    ///
    /// # Warning about blocking I/O
    ///
    /// The assumption is that the closures given to `join()` are
    /// CPU-bound tasks that do not perform I/O or other blocking
    /// operations. If you do perform I/O, and that I/O should block
    /// (e.g., waiting for a network request), the overall performance may
    /// be poor.  Moreover, if you cause one closure to be blocked waiting
    /// on another (for example, using a channel), that could lead to a
    /// deadlock.
    ///
    /// # Panics
    ///
    /// No matter what happens, both closures will always be executed.  If
    /// a single closure panics, whether it be the first or second
    /// closure, that panic will be propagated and hence `join()` will
    /// panic with the same panic value. If both closures panic, `join()`
    /// will panic with the panic value from the first closure.
    pub fn join<A, B, RA, RB>(oper_a: A, oper_b: B) -> (RA, RB)
    where
        A: FnOnce() -> RA + Send,
        B: FnOnce() -> RB + Send,
        RA: Send,
        RB: Send,
    {
        join_context(|_| oper_a(), |_| oper_b())
    }

    /// Identical to `join`, except that the closures have a parameter
    /// that provides context for the way the closure has been called,
    /// especially indicating whether they're executing on a different
    /// thread than where `join_context` was called.  This will occur if
    /// the second job is stolen by a different thread, or if
    /// `join_context` was called from outside the thread pool to begin
    /// with.
    pub fn join_context<A, B, RA, RB>(oper_a: A, oper_b: B) -> (RA, RB)
    where
        A: FnOnce(FnContext) -> RA + Send,
        B: FnOnce(FnContext) -> RB + Send,
        RA: Send,
        RB: Send,
    {
        registry::in_worker(|worker_thread, injected| unsafe {
            log!(Join {
                worker: worker_thread.index()
            });

            // Create virtual wrapper for task b; this all has to be
            // done here so that the stack frame can keep it all live
            // long enough.
            let job_b = StackJob::new(
                |migrated| oper_b(FnContext::new(migrated)),
                SpinLatch::new(),
            );
            let job_b_ref = job_b.as_job_ref();
            worker_thread.push(job_b_ref);

            // Execute task a; hopefully b gets stolen in the meantime.
            let status_a = unwind::halt_unwinding(move || oper_a(FnContext::new(injected)));
            let result_a = match status_a {
                Ok(v) => v,
                Err(err) => join_recover_from_panic(worker_thread, &job_b.latch, err),
            };

            // Now that task A has finished, try to pop job B from the
            // local stack.  It may already have been popped by job A; it
            // may also have been stolen. There may also be some tasks
            // pushed on top of it in the stack, and we will have to pop
            // those off to get to it.
            while !job_b.latch.probe() {
                if let Some(job) = worker_thread.take_local_job() {
                    if job == job_b_ref {
                        // Found it! Let's run it.
                        //
                        // Note that this could panic, but it's ok if we unwind here.
                        log!(PoppedRhs {
                            worker: worker_thread.index()
                        });
                        let result_b = job_b.run_inline(injected);
                        return (result_a, result_b);
                    } else {
                        log!(PoppedJob {
                            worker: worker_thread.index()
                        });
                        worker_thread.execute(job);
                    }
                } else {
                    // Local deque is empty. Time to steal from other
                    // threads.
                    log!(LostJob {
                        worker: worker_thread.index()
                    });
                    worker_thread.wait_until(&job_b.latch);
                    debug_assert!(job_b.latch.probe());
                    break;
                }
            }

            (result_a, job_b.into_result())
        })
    }

    /// If job A panics, we still cannot return until we are sure that job
    /// B is complete. This is because it may contain references into the
    /// enclosing stack frame(s).
    #[cold] // cold path
    unsafe fn join_recover_from_panic(
        worker_thread: &WorkerThread,
        job_b_latch: &SpinLatch,
        err: Box<Any + Send>,
    ) -> ! {
        worker_thread.wait_until(job_b_latch);
        unwind::resume_unwinding(err)
    }

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