Initial vendor packages

Signed-off-by: Valentin Popov <valentin@popov.link>

1 files changed, 995 insertions, 0 deletions

diff --git a/vendor/rayon-core/src/registry.rs b/vendor/rayon-core/src/registry.rs
new file mode 100644
index 0000000..e4f2ac7
--- /dev/null
+++ b/vendor/rayon-core/src/registry.rs
@@ -0,0 +1,995 @@
+use crate::job::{JobFifo, JobRef, StackJob};
+use crate::latch::{AsCoreLatch, CoreLatch, Latch, LatchRef, LockLatch, OnceLatch, SpinLatch};
+use crate::sleep::Sleep;
+use crate::unwind;
+use crate::{
+    ErrorKind, ExitHandler, PanicHandler, StartHandler, ThreadPoolBuildError, ThreadPoolBuilder,
+    Yield,
+};
+use crossbeam_deque::{Injector, Steal, Stealer, Worker};
+use std::cell::Cell;
+use std::collections::hash_map::DefaultHasher;
+use std::fmt;
+use std::hash::Hasher;
+use std::io;
+use std::mem;
+use std::ptr;
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::{Arc, Mutex, Once};
+use std::thread;
+use std::usize;
+
+/// Thread builder used for customization via
+/// [`ThreadPoolBuilder::spawn_handler`](struct.ThreadPoolBuilder.html#method.spawn_handler).
+pub struct ThreadBuilder {
+    name: Option<String>,
+    stack_size: Option<usize>,
+    worker: Worker<JobRef>,
+    stealer: Stealer<JobRef>,
+    registry: Arc<Registry>,
+    index: usize,
+}
+
+impl ThreadBuilder {
+    /// Gets the index of this thread in the pool, within `0..num_threads`.
+    pub fn index(&self) -> usize {
+        self.index
+    }
+
+    /// Gets the string that was specified by `ThreadPoolBuilder::name()`.
+    pub fn name(&self) -> Option<&str> {
+        self.name.as_deref()
+    }
+
+    /// Gets the value that was specified by `ThreadPoolBuilder::stack_size()`.
+    pub fn stack_size(&self) -> Option<usize> {
+        self.stack_size
+    }
+
+    /// Executes the main loop for this thread. This will not return until the
+    /// thread pool is dropped.
+    pub fn run(self) {
+        unsafe { main_loop(self) }
+    }
+}
+
+impl fmt::Debug for ThreadBuilder {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("ThreadBuilder")
+            .field("pool", &self.registry.id())
+            .field("index", &self.index)
+            .field("name", &self.name)
+            .field("stack_size", &self.stack_size)
+            .finish()
+    }
+}
+
+/// Generalized trait for spawning a thread in the `Registry`.
+///
+/// This trait is pub-in-private -- E0445 forces us to make it public,
+/// but we don't actually want to expose these details in the API.
+pub trait ThreadSpawn {
+    private_decl! {}
+
+    /// Spawn a thread with the `ThreadBuilder` parameters, and then
+    /// call `ThreadBuilder::run()`.
+    fn spawn(&mut self, thread: ThreadBuilder) -> io::Result<()>;
+}
+
+/// Spawns a thread in the "normal" way with `std::thread::Builder`.
+///
+/// This type is pub-in-private -- E0445 forces us to make it public,
+/// but we don't actually want to expose these details in the API.
+#[derive(Debug, Default)]
+pub struct DefaultSpawn;
+
+impl ThreadSpawn for DefaultSpawn {
+    private_impl! {}
+
+    fn spawn(&mut self, thread: ThreadBuilder) -> io::Result<()> {
+        let mut b = thread::Builder::new();
+        if let Some(name) = thread.name() {
+            b = b.name(name.to_owned());
+        }
+        if let Some(stack_size) = thread.stack_size() {
+            b = b.stack_size(stack_size);
+        }
+        b.spawn(|| thread.run())?;
+        Ok(())
+    }
+}
+
+/// Spawns a thread with a user's custom callback.
+///
+/// This type is pub-in-private -- E0445 forces us to make it public,
+/// but we don't actually want to expose these details in the API.
+#[derive(Debug)]
+pub struct CustomSpawn<F>(F);
+
+impl<F> CustomSpawn<F>
+where
+    F: FnMut(ThreadBuilder) -> io::Result<()>,
+{
+    pub(super) fn new(spawn: F) -> Self {
+        CustomSpawn(spawn)
+    }
+}
+
+impl<F> ThreadSpawn for CustomSpawn<F>
+where
+    F: FnMut(ThreadBuilder) -> io::Result<()>,
+{
+    private_impl! {}
+
+    #[inline]
+    fn spawn(&mut self, thread: ThreadBuilder) -> io::Result<()> {
+        (self.0)(thread)
+    }
+}
+
+pub(super) struct Registry {
+    thread_infos: Vec<ThreadInfo>,
+    sleep: Sleep,
+    injected_jobs: Injector<JobRef>,
+    broadcasts: Mutex<Vec<Worker<JobRef>>>,
+    panic_handler: Option<Box<PanicHandler>>,
+    start_handler: Option<Box<StartHandler>>,
+    exit_handler: Option<Box<ExitHandler>>,
+
+    // When this latch reaches 0, it means that all work on this
+    // registry must be complete. This is ensured in the following ways:
+    //
+    // - if this is the global registry, there is a ref-count that never
+    //   gets released.
+    // - if this is a user-created thread-pool, then so long as the thread-pool
+    //   exists, it holds a reference.
+    // - when we inject a "blocking job" into the registry with `ThreadPool::install()`,
+    //   no adjustment is needed; the `ThreadPool` holds the reference, and since we won't
+    //   return until the blocking job is complete, that ref will continue to be held.
+    // - when `join()` or `scope()` is invoked, similarly, no adjustments are needed.
+    //   These are always owned by some other job (e.g., one injected by `ThreadPool::install()`)
+    //   and that job will keep the pool alive.
+    terminate_count: AtomicUsize,
+}
+
+/// ////////////////////////////////////////////////////////////////////////
+/// Initialization
+
+static mut THE_REGISTRY: Option<Arc<Registry>> = None;
+static THE_REGISTRY_SET: Once = Once::new();
+
+/// Starts the worker threads (if that has not already happened). If
+/// initialization has not already occurred, use the default
+/// configuration.
+pub(super) fn global_registry() -> &'static Arc<Registry> {
+    set_global_registry(default_global_registry)
+        .or_else(|err| unsafe { THE_REGISTRY.as_ref().ok_or(err) })
+        .expect("The global thread pool has not been initialized.")
+}
+
+/// Starts the worker threads (if that has not already happened) with
+/// the given builder.
+pub(super) fn init_global_registry<S>(
+    builder: ThreadPoolBuilder<S>,
+) -> Result<&'static Arc<Registry>, ThreadPoolBuildError>
+where
+    S: ThreadSpawn,
+{
+    set_global_registry(|| Registry::new(builder))
+}
+
+/// Starts the worker threads (if that has not already happened)
+/// by creating a registry with the given callback.
+fn set_global_registry<F>(registry: F) -> Result<&'static Arc<Registry>, ThreadPoolBuildError>
+where
+    F: FnOnce() -> Result<Arc<Registry>, ThreadPoolBuildError>,
+{
+    let mut result = Err(ThreadPoolBuildError::new(
+        ErrorKind::GlobalPoolAlreadyInitialized,
+    ));
+
+    THE_REGISTRY_SET.call_once(|| {
+        result = registry()
+            .map(|registry: Arc<Registry>| unsafe { &*THE_REGISTRY.get_or_insert(registry) })
+    });
+
+    result
+}
+
+fn default_global_registry() -> Result<Arc<Registry>, ThreadPoolBuildError> {
+    let result = Registry::new(ThreadPoolBuilder::new());
+
+    // If we're running in an environment that doesn't support threads at all, we can fall back to
+    // using the current thread alone. This is crude, and probably won't work for non-blocking
+    // calls like `spawn` or `broadcast_spawn`, but a lot of stuff does work fine.
+    //
+    // Notably, this allows current WebAssembly targets to work even though their threading support
+    // is stubbed out, and we won't have to change anything if they do add real threading.
+    let unsupported = matches!(&result, Err(e) if e.is_unsupported());
+    if unsupported && WorkerThread::current().is_null() {
+        let builder = ThreadPoolBuilder::new().num_threads(1).use_current_thread();
+        let fallback_result = Registry::new(builder);
+        if fallback_result.is_ok() {
+            return fallback_result;
+        }
+    }
+
+    result
+}
+
+struct Terminator<'a>(&'a Arc<Registry>);
+
+impl<'a> Drop for Terminator<'a> {
+    fn drop(&mut self) {
+        self.0.terminate()
+    }
+}
+
+impl Registry {
+    pub(super) fn new<S>(
+        mut builder: ThreadPoolBuilder<S>,
+    ) -> Result<Arc<Self>, ThreadPoolBuildError>
+    where
+        S: ThreadSpawn,
+    {
+        // Soft-limit the number of threads that we can actually support.
+        let n_threads = Ord::min(builder.get_num_threads(), crate::max_num_threads());
+
+        let breadth_first = builder.get_breadth_first();
+
+        let (workers, stealers): (Vec<_>, Vec<_>) = (0..n_threads)
+            .map(|_| {
+                let worker = if breadth_first {
+                    Worker::new_fifo()
+                } else {
+                    Worker::new_lifo()
+                };
+
+                let stealer = worker.stealer();
+                (worker, stealer)
+            })
+            .unzip();
+
+        let (broadcasts, broadcast_stealers): (Vec<_>, Vec<_>) = (0..n_threads)
+            .map(|_| {
+                let worker = Worker::new_fifo();
+                let stealer = worker.stealer();
+                (worker, stealer)
+            })
+            .unzip();
+
+        let registry = Arc::new(Registry {
+            thread_infos: stealers.into_iter().map(ThreadInfo::new).collect(),
+            sleep: Sleep::new(n_threads),
+            injected_jobs: Injector::new(),
+            broadcasts: Mutex::new(broadcasts),
+            terminate_count: AtomicUsize::new(1),
+            panic_handler: builder.take_panic_handler(),
+            start_handler: builder.take_start_handler(),
+            exit_handler: builder.take_exit_handler(),
+        });
+
+        // If we return early or panic, make sure to terminate existing threads.
+        let t1000 = Terminator(&registry);
+
+        for (index, (worker, stealer)) in workers.into_iter().zip(broadcast_stealers).enumerate() {
+            let thread = ThreadBuilder {
+                name: builder.get_thread_name(index),
+                stack_size: builder.get_stack_size(),
+                registry: Arc::clone(&registry),
+                worker,
+                stealer,
+                index,
+            };
+
+            if index == 0 && builder.use_current_thread {
+                if !WorkerThread::current().is_null() {
+                    return Err(ThreadPoolBuildError::new(
+                        ErrorKind::CurrentThreadAlreadyInPool,
+                    ));
+                }
+                // Rather than starting a new thread, we're just taking over the current thread
+                // *without* running the main loop, so we can still return from here.
+                // The WorkerThread is leaked, but we never shutdown the global pool anyway.
+                let worker_thread = Box::into_raw(Box::new(WorkerThread::from(thread)));
+
+                unsafe {
+                    WorkerThread::set_current(worker_thread);
+                    Latch::set(&registry.thread_infos[index].primed);
+                }
+                continue;
+            }
+
+            if let Err(e) = builder.get_spawn_handler().spawn(thread) {
+                return Err(ThreadPoolBuildError::new(ErrorKind::IOError(e)));
+            }
+        }
+
+        // Returning normally now, without termination.
+        mem::forget(t1000);
+
+        Ok(registry)
+    }
+
+    pub(super) fn current() -> Arc<Registry> {
+        unsafe {
+            let worker_thread = WorkerThread::current();
+            let registry = if worker_thread.is_null() {
+                global_registry()
+            } else {
+                &(*worker_thread).registry
+            };
+            Arc::clone(registry)
+        }
+    }
+
+    /// Returns the number of threads in the current registry.  This
+    /// is better than `Registry::current().num_threads()` because it
+    /// avoids incrementing the `Arc`.
+    pub(super) fn current_num_threads() -> usize {
+        unsafe {
+            let worker_thread = WorkerThread::current();
+            if worker_thread.is_null() {
+                global_registry().num_threads()
+            } else {
+                (*worker_thread).registry.num_threads()
+            }
+        }
+    }
+
+    /// Returns the current `WorkerThread` if it's part of this `Registry`.
+    pub(super) fn current_thread(&self) -> Option<&WorkerThread> {
+        unsafe {
+            let worker = WorkerThread::current().as_ref()?;
+            if worker.registry().id() == self.id() {
+                Some(worker)
+            } else {
+                None
+            }
+        }
+    }
+
+    /// Returns an opaque identifier for this registry.
+    pub(super) fn id(&self) -> RegistryId {
+        // We can rely on `self` not to change since we only ever create
+        // registries that are boxed up in an `Arc` (see `new()` above).
+        RegistryId {
+            addr: self as *const Self as usize,
+        }
+    }
+
+    pub(super) fn num_threads(&self) -> usize {
+        self.thread_infos.len()
+    }
+
+    pub(super) fn catch_unwind(&self, f: impl FnOnce()) {
+        if let Err(err) = unwind::halt_unwinding(f) {
+            // If there is no handler, or if that handler itself panics, then we abort.
+            let abort_guard = unwind::AbortIfPanic;
+            if let Some(ref handler) = self.panic_handler {
+                handler(err);
+                mem::forget(abort_guard);
+            }
+        }
+    }
+
+    /// Waits for the worker threads to get up and running.  This is
+    /// meant to be used for benchmarking purposes, primarily, so that
+    /// you can get more consistent numbers by having everything
+    /// "ready to go".
+    pub(super) fn wait_until_primed(&self) {
+        for info in &self.thread_infos {
+            info.primed.wait();
+        }
+    }
+
+    /// Waits for the worker threads to stop. This is used for testing
+    /// -- so we can check that termination actually works.
+    #[cfg(test)]
+    pub(super) fn wait_until_stopped(&self) {
+        for info in &self.thread_infos {
+            info.stopped.wait();
+        }
+    }
+
+    /// ////////////////////////////////////////////////////////////////////////
+    /// MAIN LOOP
+    ///
+    /// So long as all of the worker threads are hanging out in their
+    /// top-level loop, there is no work to be done.
+
+    /// Push a job into the given `registry`. If we are running on a
+    /// worker thread for the registry, this will push onto the
+    /// deque. Else, it will inject from the outside (which is slower).
+    pub(super) fn inject_or_push(&self, job_ref: JobRef) {
+        let worker_thread = WorkerThread::current();
+        unsafe {
+            if !worker_thread.is_null() && (*worker_thread).registry().id() == self.id() {
+                (*worker_thread).push(job_ref);
+            } else {
+                self.inject(job_ref);
+            }
+        }
+    }
+
+    /// Push a job into the "external jobs" queue; it will be taken by
+    /// whatever worker has nothing to do. Use this if you know that
+    /// you are not on a worker of this registry.
+    pub(super) fn inject(&self, injected_job: JobRef) {
+        // It should not be possible for `state.terminate` to be true
+        // here. It is only set to true when the user creates (and
+        // drops) a `ThreadPool`; and, in that case, they cannot be
+        // calling `inject()` later, since they dropped their
+        // `ThreadPool`.
+        debug_assert_ne!(
+            self.terminate_count.load(Ordering::Acquire),
+            0,
+            "inject() sees state.terminate as true"
+        );
+
+        let queue_was_empty = self.injected_jobs.is_empty();
+
+        self.injected_jobs.push(injected_job);
+        self.sleep.new_injected_jobs(1, queue_was_empty);
+    }
+
+    fn has_injected_job(&self) -> bool {
+        !self.injected_jobs.is_empty()
+    }
+
+    fn pop_injected_job(&self) -> Option<JobRef> {
+        loop {
+            match self.injected_jobs.steal() {
+                Steal::Success(job) => return Some(job),
+                Steal::Empty => return None,
+                Steal::Retry => {}
+            }
+        }
+    }
+
+    /// Push a job into each thread's own "external jobs" queue; it will be
+    /// executed only on that thread, when it has nothing else to do locally,
+    /// before it tries to steal other work.
+    ///
+    /// **Panics** if not given exactly as many jobs as there are threads.
+    pub(super) fn inject_broadcast(&self, injected_jobs: impl ExactSizeIterator<Item = JobRef>) {
+        assert_eq!(self.num_threads(), injected_jobs.len());
+        {
+            let broadcasts = self.broadcasts.lock().unwrap();
+
+            // It should not be possible for `state.terminate` to be true
+            // here. It is only set to true when the user creates (and
+            // drops) a `ThreadPool`; and, in that case, they cannot be
+            // calling `inject_broadcast()` later, since they dropped their
+            // `ThreadPool`.
+            debug_assert_ne!(
+                self.terminate_count.load(Ordering::Acquire),
+                0,
+                "inject_broadcast() sees state.terminate as true"
+            );
+
+            assert_eq!(broadcasts.len(), injected_jobs.len());
+            for (worker, job_ref) in broadcasts.iter().zip(injected_jobs) {
+                worker.push(job_ref);
+            }
+        }
+        for i in 0..self.num_threads() {
+            self.sleep.notify_worker_latch_is_set(i);
+        }
+    }
+
+    /// If already in a worker-thread of this registry, just execute `op`.
+    /// Otherwise, inject `op` in this thread-pool. Either way, block until `op`
+    /// completes and return its return value. If `op` panics, that panic will
+    /// be propagated as well.  The second argument indicates `true` if injection
+    /// was performed, `false` if executed directly.
+    pub(super) fn in_worker<OP, R>(&self, op: OP) -> R
+    where
+        OP: FnOnce(&WorkerThread, bool) -> R + Send,
+        R: Send,
+    {
+        unsafe {
+            let worker_thread = WorkerThread::current();
+            if worker_thread.is_null() {
+                self.in_worker_cold(op)
+            } else if (*worker_thread).registry().id() != self.id() {
+                self.in_worker_cross(&*worker_thread, op)
+            } else {
+                // Perfectly valid to give them a `&T`: this is the
+                // current thread, so we know the data structure won't be
+                // invalidated until we return.
+                op(&*worker_thread, false)
+            }
+        }
+    }
+
+    #[cold]
+    unsafe fn in_worker_cold<OP, R>(&self, op: OP) -> R
+    where
+        OP: FnOnce(&WorkerThread, bool) -> R + Send,
+        R: Send,
+    {
+        thread_local!(static LOCK_LATCH: LockLatch = LockLatch::new());
+
+        LOCK_LATCH.with(|l| {
+            // This thread isn't a member of *any* thread pool, so just block.
+            debug_assert!(WorkerThread::current().is_null());
+            let job = StackJob::new(
+                |injected| {
+                    let worker_thread = WorkerThread::current();
+                    assert!(injected && !worker_thread.is_null());
+                    op(&*worker_thread, true)
+                },
+                LatchRef::new(l),
+            );
+            self.inject(job.as_job_ref());
+            job.latch.wait_and_reset(); // Make sure we can use the same latch again next time.
+
+            job.into_result()
+        })
+    }
+
+    #[cold]
+    unsafe fn in_worker_cross<OP, R>(&self, current_thread: &WorkerThread, op: OP) -> R
+    where
+        OP: FnOnce(&WorkerThread, bool) -> R + Send,
+        R: Send,
+    {
+        // This thread is a member of a different pool, so let it process
+        // other work while waiting for this `op` to complete.
+        debug_assert!(current_thread.registry().id() != self.id());
+        let latch = SpinLatch::cross(current_thread);
+        let job = StackJob::new(
+            |injected| {
+                let worker_thread = WorkerThread::current();
+                assert!(injected && !worker_thread.is_null());
+                op(&*worker_thread, true)
+            },
+            latch,
+        );
+        self.inject(job.as_job_ref());
+        current_thread.wait_until(&job.latch);
+        job.into_result()
+    }
+
+    /// Increments the terminate counter. This increment should be
+    /// balanced by a call to `terminate`, which will decrement. This
+    /// is used when spawning asynchronous work, which needs to
+    /// prevent the registry from terminating so long as it is active.
+    ///
+    /// Note that blocking functions such as `join` and `scope` do not
+    /// need to concern themselves with this fn; their context is
+    /// responsible for ensuring the current thread-pool will not
+    /// terminate until they return.
+    ///
+    /// The global thread-pool always has an outstanding reference
+    /// (the initial one). Custom thread-pools have one outstanding
+    /// reference that is dropped when the `ThreadPool` is dropped:
+    /// since installing the thread-pool blocks until any joins/scopes
+    /// complete, this ensures that joins/scopes are covered.
+    ///
+    /// The exception is `::spawn()`, which can create a job outside
+    /// of any blocking scope. In that case, the job itself holds a
+    /// terminate count and is responsible for invoking `terminate()`
+    /// when finished.
+    pub(super) fn increment_terminate_count(&self) {
+        let previous = self.terminate_count.fetch_add(1, Ordering::AcqRel);
+        debug_assert!(previous != 0, "registry ref count incremented from zero");
+        assert!(
+            previous != std::usize::MAX,
+            "overflow in registry ref count"
+        );
+    }
+
+    /// Signals that the thread-pool which owns this registry has been
+    /// dropped. The worker threads will gradually terminate, once any
+    /// extant work is completed.
+    pub(super) fn terminate(&self) {
+        if self.terminate_count.fetch_sub(1, Ordering::AcqRel) == 1 {
+            for (i, thread_info) in self.thread_infos.iter().enumerate() {
+                unsafe { OnceLatch::set_and_tickle_one(&thread_info.terminate, self, i) };
+            }
+        }
+    }
+
+    /// Notify the worker that the latch they are sleeping on has been "set".
+    pub(super) fn notify_worker_latch_is_set(&self, target_worker_index: usize) {
+        self.sleep.notify_worker_latch_is_set(target_worker_index);
+    }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
+pub(super) struct RegistryId {
+    addr: usize,
+}
+
+struct ThreadInfo {
+    /// Latch set once thread has started and we are entering into the
+    /// main loop. Used to wait for worker threads to become primed,
+    /// primarily of interest for benchmarking.
+    primed: LockLatch,
+
+    /// Latch is set once worker thread has completed. Used to wait
+    /// until workers have stopped; only used for tests.
+    stopped: LockLatch,
+
+    /// The latch used to signal that terminated has been requested.
+    /// This latch is *set* by the `terminate` method on the
+    /// `Registry`, once the registry's main "terminate" counter
+    /// reaches zero.
+    terminate: OnceLatch,
+
+    /// the "stealer" half of the worker's deque
+    stealer: Stealer<JobRef>,
+}
+
+impl ThreadInfo {
+    fn new(stealer: Stealer<JobRef>) -> ThreadInfo {
+        ThreadInfo {
+            primed: LockLatch::new(),
+            stopped: LockLatch::new(),
+            terminate: OnceLatch::new(),
+            stealer,
+        }
+    }
+}
+
+/// ////////////////////////////////////////////////////////////////////////
+/// WorkerThread identifiers
+
+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()) };
+}
+
+impl From<ThreadBuilder> for WorkerThread {
+    fn from(thread: ThreadBuilder) -> Self {
+        Self {
+            worker: thread.worker,
+            stealer: thread.stealer,
+            fifo: JobFifo::new(),
+            index: thread.index,
+            rng: XorShift64Star::new(),
+            registry: thread.registry,
+        }
+    }
+}
+
+impl Drop for WorkerThread {
+    fn drop(&mut self) {
+        // Undo `set_current`
+        WORKER_THREAD_STATE.with(|t| {
+            assert!(t.get().eq(&(self as *const _)));
+            t.set(ptr::null());
+        });
+    }
+}
+
+impl WorkerThread {
+    /// Gets the `WorkerThread` index for the current thread; returns
+    /// NULL if this is not a worker thread. This pointer is valid
+    /// anywhere on the current thread.
+    #[inline]
+    pub(super) fn current() -> *const WorkerThread {
+        WORKER_THREAD_STATE.with(Cell::get)
+    }
+
+    /// Sets `self` as the worker thread index for the current thread.
+    /// This is done during worker thread startup.
+    unsafe fn set_current(thread: *const WorkerThread) {
+        WORKER_THREAD_STATE.with(|t| {
+            assert!(t.get().is_null());
+            t.set(thread);
+        });
+    }
+
+    /// Returns the registry that owns this worker thread.
+    #[inline]
+    pub(super) fn registry(&self) -> &Arc<Registry> {
+        &self.registry
+    }
+
+    /// Our index amongst the worker threads (ranges from `0..self.num_threads()`).
+    #[inline]
+    pub(super) fn index(&self) -> usize {
+        self.index
+    }
+
+    #[inline]
+    pub(super) unsafe fn push(&self, job: JobRef) {
+        let queue_was_empty = self.worker.is_empty();
+        self.worker.push(job);
+        self.registry.sleep.new_internal_jobs(1, queue_was_empty);
+    }
+
+    #[inline]
+    pub(super) unsafe fn push_fifo(&self, job: JobRef) {
+        self.push(self.fifo.push(job));
+    }
+
+    #[inline]
+    pub(super) fn local_deque_is_empty(&self) -> bool {
+        self.worker.is_empty()
+    }
+
+    /// Attempts to obtain a "local" job -- typically this means
+    /// popping from the top of the stack, though if we are configured
+    /// for breadth-first execution, it would mean dequeuing from the
+    /// bottom.
+    #[inline]
+    pub(super) fn take_local_job(&self) -> Option<JobRef> {
+        let popped_job = self.worker.pop();
+
+        if popped_job.is_some() {
+            return popped_job;
+        }
+
+        loop {
+            match self.stealer.steal() {
+                Steal::Success(job) => return Some(job),
+                Steal::Empty => return None,
+                Steal::Retry => {}
+            }
+        }
+    }
+
+    fn has_injected_job(&self) -> bool {
+        !self.stealer.is_empty() || self.registry.has_injected_job()
+    }
+
+    /// Wait until the latch is set. Try to keep busy by popping and
+    /// stealing tasks as necessary.
+    #[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
+    }
+
+    unsafe fn wait_until_out_of_work(&self) {
+        debug_assert_eq!(self as *const _, WorkerThread::current());
+        let registry = &*self.registry;
+        let index = self.index;
+
+        self.wait_until(&registry.thread_infos[index].terminate);
+
+        // Should not be any work left in our queue.
+        debug_assert!(self.take_local_job().is_none());
+
+        // Let registry know we are done
+        Latch::set(&registry.thread_infos[index].stopped);
+    }
+
+    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())
+    }
+
+    pub(super) fn yield_now(&self) -> Yield {
+        match self.find_work() {
+            Some(job) => unsafe {
+                self.execute(job);
+                Yield::Executed
+            },
+            None => Yield::Idle,
+        }
+    }
+
+    pub(super) fn yield_local(&self) -> Yield {
+        match self.take_local_job() {
+            Some(job) => unsafe {
+                self.execute(job);
+                Yield::Executed
+            },
+            None => Yield::Idle,
+        }
+    }
+
+    #[inline]
+    pub(super) unsafe fn execute(&self, job: JobRef) {
+        job.execute();
+    }
+
+    /// Try to steal a single job and return it.
+    ///
+    /// This should only be done as a last resort, when there is no
+    /// local work to do.
+    fn steal(&self) -> Option<JobRef> {
+        // we only steal when we don't have any work to do locally
+        debug_assert!(self.local_deque_is_empty());
+
+        // otherwise, try to steal
+        let thread_infos = &self.registry.thread_infos.as_slice();
+        let num_threads = thread_infos.len();
+        if num_threads <= 1 {
+            return None;
+        }
+
+        loop {
+            let mut retry = false;
+            let start = self.rng.next_usize(num_threads);
+            let job = (start..num_threads)
+                .chain(0..start)
+                .filter(move |&i| i != self.index)
+                .find_map(|victim_index| {
+                    let victim = &thread_infos[victim_index];
+                    match victim.stealer.steal() {
+                        Steal::Success(job) => Some(job),
+                        Steal::Empty => None,
+                        Steal::Retry => {
+                            retry = true;
+                            None
+                        }
+                    }
+                });
+            if job.is_some() || !retry {
+                return job;
+            }
+        }
+    }
+}
+
+/// ////////////////////////////////////////////////////////////////////////
+
+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 threadpool 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.
+    }
+}
+
+/// If already in a worker-thread, just execute `op`.  Otherwise,
+/// execute `op` in the default thread-pool. Either way, block until
+/// `op` completes and return its return value. If `op` panics, that
+/// panic will be propagated as well.  The second argument indicates
+/// `true` if injection was performed, `false` if executed directly.
+pub(super) fn in_worker<OP, R>(op: OP) -> R
+where
+    OP: FnOnce(&WorkerThread, bool) -> R + Send,
+    R: Send,
+{
+    unsafe {
+        let owner_thread = WorkerThread::current();
+        if !owner_thread.is_null() {
+            // Perfectly valid to give them a `&T`: this is the
+            // current thread, so we know the data structure won't be
+            // invalidated until we return.
+            op(&*owner_thread, false)
+        } else {
+            global_registry().in_worker(op)
+        }
+    }
+}
+
+/// [xorshift*] is a fast pseudorandom number generator which will
+/// even tolerate weak seeding, as long as it's not zero.
+///
+/// [xorshift*]: https://en.wikipedia.org/wiki/Xorshift#xorshift*
+struct XorShift64Star {
+    state: Cell<u64>,
+}
+
+impl XorShift64Star {
+    fn new() -> Self {
+        // Any non-zero seed will do -- this uses the hash of a global counter.
+        let mut seed = 0;
+        while seed == 0 {
+            let mut hasher = DefaultHasher::new();
+            static COUNTER: AtomicUsize = AtomicUsize::new(0);
+            hasher.write_usize(COUNTER.fetch_add(1, Ordering::Relaxed));
+            seed = hasher.finish();
+        }
+
+        XorShift64Star {
+            state: Cell::new(seed),
+        }
+    }
+
+    fn next(&self) -> u64 {
+        let mut x = self.state.get();
+        debug_assert_ne!(x, 0);
+        x ^= x >> 12;
+        x ^= x << 25;
+        x ^= x >> 27;
+        self.state.set(x);
+        x.wrapping_mul(0x2545_f491_4f6c_dd1d)
+    }
+
+    /// Return a value from `0..n`.
+    fn next_usize(&self, n: usize) -> usize {
+        (self.next() % n as u64) as usize
+    }
+}