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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(®istry);
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(®istry),
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(®istry.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(®istry.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(®istry.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(®istry.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.
///
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
}
}