rayon 0.4.3

use latch::Latch;
use std::any::Any;
use std::cell::UnsafeCell;
use std::mem;
use unwind;

enum JobResult<T> {
    None,
    Ok(T),
    Panic(Box<Any + Send>),
}

/// A `Job` is used to advertise work for other threads that they may
/// want to steal. In accordance with time honored tradition, jobs are
/// arranged in a deque, so that thieves can take from the top of the
/// deque while the main worker manages the bottom of the deque. This
/// deque is managed by the `thread_pool` module.
pub trait Job {
    unsafe fn execute(this: *const Self, mode: JobMode);
}

pub enum JobMode {
    Execute,
    Abort,
}

/// Effectively a Job trait object. Each JobRef **must** be executed
/// exactly once, or else data may leak.
///
/// Internally, we store the job's data in a `*const ()` pointer.  The
/// true type is something like `*const StackJob<...>`, but we hide
/// it. We also carry the "execute fn" from the `Job` trait.
#[derive(Copy, Clone)]
pub struct JobRef {
    pointer: *const (),
    execute_fn: unsafe fn(*const (), mode: JobMode),
}

unsafe impl Send for JobRef {}
unsafe impl Sync for JobRef {}

impl JobRef {
    pub unsafe fn new<T>(data: *const T) -> JobRef
        where T: Job
    {
        let fn_ptr: unsafe fn(*const T, JobMode) = <T as Job>::execute;

        // erase types:
        let fn_ptr: unsafe fn(*const (), JobMode) = mem::transmute(fn_ptr);
        let pointer = data as *const ();

        JobRef { pointer: pointer, execute_fn: fn_ptr }
    }

    #[inline]
    pub unsafe fn execute(&self, mode: JobMode) {
        (self.execute_fn)(self.pointer, mode)
    }
}

/// A job that will be owned by a stack slot. This means that when it
/// executes it need not free any heap data, the cleanup occurs when
/// the stack frame is later popped.
pub struct StackJob<L: Latch, F, R> {
    pub latch: L,
    func: UnsafeCell<Option<F>>,
    result: UnsafeCell<JobResult<R>>,
}

impl<L: Latch, F, R> StackJob<L, F, R>
    where F: FnOnce() -> R
{
    pub fn new(func: F, latch: L) -> StackJob<L, F, R> {
        StackJob {
            latch: latch,
            func: UnsafeCell::new(Some(func)),
            result: UnsafeCell::new(JobResult::None),
        }
    }

    pub unsafe fn as_job_ref(&self) -> JobRef {
        JobRef::new(self)
    }

    pub unsafe fn run_inline(self) -> R {
        self.func.into_inner().unwrap()()
    }

    pub unsafe fn into_result(self) -> R {
        match self.result.into_inner() {
            JobResult::None => unreachable!(),
            JobResult::Ok(x) => x,
            JobResult::Panic(x) => unwind::resume_unwinding(x),
        }
    }
}

impl<L: Latch, F, R> Job for StackJob<L, F, R>
    where F: FnOnce() -> R
{
    unsafe fn execute(this: *const Self, mode: JobMode) {
        let this = &*this;
        match mode {
            JobMode::Execute => {
                let abort = unwind::AbortIfPanic;
                let func = (*this.func.get()).take().unwrap();
                (*this.result.get()) = match unwind::halt_unwinding(|| func()) {
                    Ok(x) => JobResult::Ok(x),
                    Err(x) => JobResult::Panic(x),
                };
                this.latch.set();
                mem::forget(abort);
            }
            JobMode::Abort => {
                this.latch.set();
            }
        }
    }
}