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smol
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This commit is contained in:
Stjepan Glavina 2020-06-05 14:23:02 +02:00
parent e6bd9229f7
commit 0408c19531
4 changed files with 225 additions and 58 deletions
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187
src/io_parking.rs Normal file
View File

@ -0,0 +1,187 @@
use std::fmt;
use std::marker::PhantomData;
use std::sync::atomic::AtomicUsize;
use std::sync::atomic::Ordering::SeqCst;
use std::sync::{Arc, Condvar, Mutex};
use std::time::{Duration, Instant};
use crate::reactor::{Reactor, ReactorLock};
pub(crate) struct IoParker {
unparker: IoUnparker,
_marker: PhantomData<*const ()>,
}
unsafe impl Send for IoParker {}
impl IoParker {
pub fn new() -> IoParker {
IoParker {
unparker: IoUnparker {
inner: Arc::new(Inner {
state: AtomicUsize::new(EMPTY),
lock: Mutex::new(()),
cvar: Condvar::new(),
}),
},
_marker: PhantomData,
}
}
pub fn park(&self) {
self.unparker.inner.park(None);
}
pub fn park_timeout(&self, timeout: Duration) -> bool {
self.unparker.inner.park(Some(timeout))
}
pub fn park_deadline(&self, deadline: Instant) -> bool {
self.unparker
.inner
.park(Some(deadline.saturating_duration_since(Instant::now())))
}
pub fn unpark(&self) {
self.unparker.unpark()
}
pub fn unparker(&self) -> IoUnparker {
self.unparker.clone()
}
}
impl fmt::Debug for IoParker {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.pad("IoParker { .. }")
}
}
pub(crate) struct IoUnparker {
inner: Arc<Inner>,
}
unsafe impl Send for IoUnparker {}
unsafe impl Sync for IoUnparker {}
impl IoUnparker {
pub fn unpark(&self) {
self.inner.unpark()
}
}
impl fmt::Debug for IoUnparker {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.pad("IoUnparker { .. }")
}
}
impl Clone for IoUnparker {
fn clone(&self) -> IoUnparker {
IoUnparker {
inner: self.inner.clone(),
}
}
}
const EMPTY: usize = 0;
const PARKED: usize = 1;
const NOTIFIED: usize = 2;
struct Inner {
state: AtomicUsize,
lock: Mutex<()>,
cvar: Condvar,
}
impl Inner {
fn park(&self, timeout: Option<Duration>) -> bool {
// If we were previously notified then we consume this notification and return quickly.
if self
.state
.compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst)
.is_ok()
{
return true;
}
// If the timeout is zero, then there is no need to actually block.
if let Some(dur) = timeout {
if dur == Duration::from_millis(0) {
if let Some(mut reactor_lock) = Reactor::get().try_lock() {
reactor_lock.poll().expect("failure while polling I/O");
}
return false;
}
}
// Otherwise we need to coordinate going to sleep.
let mut m = self.lock.lock().unwrap();
match self.state.compare_exchange(EMPTY, PARKED, SeqCst, SeqCst) {
Ok(_) => {}
// Consume this notification to avoid spurious wakeups in the next park.
Err(NOTIFIED) => {
// We must read `state` here, even though we know it will be `NOTIFIED`. This is
// because `unpark` may have been called again since we read `NOTIFIED` in the
// `compare_exchange` above. We must perform an acquire operation that synchronizes
// with that `unpark` to observe any writes it made before the call to `unpark`. To
// do that we must read from the write it made to `state`.
let old = self.state.swap(EMPTY, SeqCst);
assert_eq!(old, NOTIFIED, "park state changed unexpectedly");
return true;
}
Err(n) => panic!("inconsistent park_timeout state: {}", n),
}
match timeout {
None => {
loop {
// Block the current thread on the conditional variable.
m = self.cvar.wait(m).unwrap();
match self.state.compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst) {
Ok(_) => return true, // got a notification
Err(_) => {} // spurious wakeup, go back to sleep
}
}
}
Some(timeout) => {
// Wait with a timeout, and if we spuriously wake up or otherwise wake up from a
// notification we just want to unconditionally set `state` back to `EMPTY`, either
// consuming a notification or un-flagging ourselves as parked.
let (_m, _result) = self.cvar.wait_timeout(m, timeout).unwrap();
match self.state.swap(EMPTY, SeqCst) {
NOTIFIED => true, // got a notification
PARKED => false, // no notification
n => panic!("inconsistent park_timeout state: {}", n),
}
}
}
}
pub fn unpark(&self) {
// To ensure the unparked thread will observe any writes we made before this call, we must
// perform a release operation that `park` can synchronize with. To do that we must write
// `NOTIFIED` even if `state` is already `NOTIFIED`. That is why this must be a swap rather
// than a compare-and-swap that returns if it reads `NOTIFIED` on failure.
match self.state.swap(NOTIFIED, SeqCst) {
EMPTY => return, // no one was waiting
NOTIFIED => return, // already unparked
PARKED => {} // gotta go wake someone up
_ => panic!("inconsistent state in unpark"),
}
// There is a period between when the parked thread sets `state` to `PARKED` (or last
// checked `state` in the case of a spurious wakeup) and when it actually waits on `cvar`.
// If we were to notify during this period it would be ignored and then when the parked
// thread went to sleep it would never wake up. Fortunately, it has `lock` locked at this
// stage so we can acquire `lock` to wait until it is ready to receive the notification.
//
// Releasing `lock` before the call to `notify_one` means that when the parked thread wakes
// it doesn't get woken only to have to wait for us to release `lock`.
drop(self.lock.lock().unwrap());
self.cvar.notify_one();
}
}

1
src/lib.rs
View File

@ -120,6 +120,7 @@ mod block_on;
mod blocking;
mod context;
mod io_event;
mod io_parking;
mod reactor;
mod run;
mod sys;

69
src/run.rs
View File

@ -14,7 +14,7 @@ use crate::io_event::IoEvent;
use crate::reactor::{Reactor, ReactorLock};
use crate::thread_local::ThreadLocalExecutor;
use crate::throttle;
use crate::work_stealing::WorkStealingExecutor;
use crate::work_stealing::{WorkStealingExecutor, Worker};
/// Runs executors and polls the reactor.
///
@ -95,30 +95,22 @@ use crate::work_stealing::WorkStealingExecutor;
/// }
/// ```
pub fn run<T>(future: impl Future<Output = T>) -> T {
// Create a thread-local executor and a worker in the work-stealing executor.
let local = ThreadLocalExecutor::new();
let event = IoEvent::new().expect("cannot create an `IoEvent`");
let ws_executor = WorkStealingExecutor::get();
let worker = ws_executor.worker();
let reactor = Reactor::get();
// Create a waker that triggers an I/O event in the thread-local scheduler.
let ev = local.event().clone();
let ev = event.clone();
let waker = async_task::waker_fn(move || ev.notify());
let cx = &mut Context::from_waker(&waker);
futures_util::pin_mut!(future);
// Set up tokio (if enabled) and the thread-locals before execution begins.
let enter = context::enter;
let enter = |f| local.enter(|| enter(f));
let enter = |f| worker.enter(|| enter(f));
enter(|| {
// A list of I/O events that indicate there is work to do.
let io_events = [local.event(), ws_executor.event()];
// Number of times this thread has yielded because it didn't find any work.
let mut yields = 0;
// We run four components at the same time, treating them all fairly and making sure none
// of them get starved:
//
@ -140,39 +132,25 @@ pub fn run<T>(future: impl Future<Output = T>) -> T {
// This way we make sure that if any changes happen that might give us new work will
// unblock epoll/kevent/wepoll and let us continue the loop.
loop {
// 1. Poll the main future.
if let Poll::Ready(val) = throttle::setup(|| future.as_mut().poll(cx)) {
return val;
}
// 2. Run a batch of tasks in the thread-local executor.
let more_local = local.execute();
// 3. Run a batch of tasks in the work-stealing executor.
let more_worker = worker.execute();
let more = worker.execute();
if more {
if let Some(mut reactor_lock) = reactor.try_lock() {
reactor_lock.poll().expect("failure while polling I/O");
}
continue;
}
// 4. Poll the reactor.
if let Some(reactor_lock) = reactor.try_lock() {
yields = 0;
react(reactor_lock, &io_events, more_local || more_worker);
react(&worker, reactor_lock, &event);
continue;
}
// If there is more work in the thread-local or the work-stealing executor, continue.
if more_local || more_worker {
yields = 0;
continue;
}
// Yield a few times if no work is found.
yields += 1;
if yields <= 2 {
thread::yield_now();
continue;
}
// If still no work is found, stop yielding and block the thread.
yields = 0;
// Prepare for blocking until the reactor is locked or `local.event()` is triggered.
//
// Note that there is no need to wait for `ws_executor.event()`. If we lock the reactor
@ -183,16 +161,16 @@ pub fn run<T>(future: impl Future<Output = T>) -> T {
// and will unlock it if there is more work to do because every worker triggers the I/O
// event whenever it finds a runnable task.
let lock = reactor.lock();
let notified = local.event().notified();
let notified = event.notified();
futures_util::pin_mut!(lock);
futures_util::pin_mut!(notified);
// Block until either the reactor is locked or `local.event()` is triggered.
if let Either::Left((reactor_lock, _)) = block_on(future::select(lock, notified)) {
react(reactor_lock, &io_events, false);
react(&worker, reactor_lock, &event);
} else {
// Clear `local.event()` because it was triggered.
local.event().clear();
event.clear();
}
}
})
@ -204,25 +182,14 @@ pub fn run<T>(future: impl Future<Output = T>) -> T {
/// Otherwise, the current thread waits on it until a timer fires or an I/O event occurs.
///
/// I/O events are cleared at the end of this function.
fn react(mut reactor_lock: ReactorLock<'_>, io_events: &[&IoEvent], mut more_tasks: bool) {
// Clear all I/O events and check if any of them were triggered.
for ev in io_events {
if ev.clear() {
more_tasks = true;
}
}
if more_tasks {
fn react(worker: &Worker<'_>, mut reactor_lock: ReactorLock<'_>, event: &IoEvent) {
if event.clear() {
// If there might be more tasks to run, just poll without blocking.
reactor_lock.poll().expect("failure while polling I/O");
} else {
// Otherwise, block until the first I/O event or a timer.
reactor_lock.wait().expect("failure while waiting on I/O");
// Clear all I/O events before dropping the lock. This is not really necessary, but
// clearing flags here might prevent a redundant wakeup in the future.
for ev in io_events {
ev.clear();
}
event.clear();
}
}

26
src/work_stealing.rs
View File

@ -21,7 +21,8 @@
use std::cell::Cell;
use std::future::Future;
use std::panic;
use std::sync::{Arc, RwLock};
use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
use std::sync::{Arc, Mutex, RwLock};
use concurrent_queue::ConcurrentQueue;
use once_cell::sync::Lazy;
@ -53,6 +54,10 @@ pub(crate) struct WorkStealingExecutor {
/// An I/O event that is triggered whenever there might be available tasks to run.
event: IoEvent,
notified: AtomicBool,
sleeping: Mutex<Vec<Arc<dyn Fn() + Send + Sync>>>,
}
impl WorkStealingExecutor {
@ -62,13 +67,20 @@ impl WorkStealingExecutor {
injector: ConcurrentQueue::unbounded(),
stealers: RwLock::new(Slab::new()),
event: IoEvent::new().expect("cannot create an `IoEvent`"),
notified: AtomicBool::new(false),
sleeping: Mutex::new(Vec::new()),
});
&EXECUTOR
}
/// Returns the event indicating there is a scheduled task.
pub fn event(&self) -> &IoEvent {
&self.event
fn notify(&self) {
// if !self.notified.compare_and_swap(false, true, Ordering::SeqCst) {
// let mut sleeping = self.sleeping.lock().unwrap();
// if let Some(callback) = sleeping.pop() {
// callback();
// }
// }
self.event.notify();
}
/// Spawns a future onto this executor.
@ -88,7 +100,7 @@ impl WorkStealingExecutor {
self.injector.push(runnable).unwrap();
// Notify workers that there is a task in the injector queue.
self.event.notify();
self.notify();
}
};
@ -169,7 +181,7 @@ impl Worker<'_> {
// need to worry about `search()` re-shuffling tasks between queues, which
// races with other workers searching for tasks. Other workers might not
// find a task while there is one! Notifying here avoids this problem.
self.executor.event.notify();
self.executor.notify();
// Run the task.
if throttle::setup(|| r.run()) {
@ -325,6 +337,6 @@ impl Drop for Worker<'_> {
// This task will not search for tasks anymore and therefore won't notify other workers if
// new tasks are found. Notify another worker to start searching right away.
self.executor.event.notify();
self.executor.notify();
}
}