smol-rs
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async-executor
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Revert "feat: Use actual thread local queues instead of using a RwLock" 

This reverts commit 7592d4188a.
This commit is contained in:
John Nunley 2024-03-23 16:03:33 -07:00 committed by John Nunley
parent c90fd306cd
commit 00dbbbf85d
4 changed files with 47 additions and 92 deletions
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4
Cargo.toml
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@ -6,7 +6,7 @@ name = "async-executor"
version = "1.9.0"
authors = ["Stjepan Glavina <stjepang@gmail.com>"]
edition = "2021"
rust-version = "1.61"
rust-version = "1.60"
description = "Async executor"
license = "Apache-2.0 OR MIT"
repository = "https://github.com/smol-rs/async-executor"
@ -17,12 +17,10 @@ exclude = ["/.*"]
[dependencies]
async-lock = "3.0.0"
async-task = "4.4.0"
atomic-waker = "1.0"
concurrent-queue = "2.0.0"
fastrand = "2.0.0"
futures-lite = { version = "2.0.0", default-features = false }
slab = "0.4.4"
thread_local = "1.1"
[target.'cfg(target_family = "wasm")'.dependencies]
futures-lite = { version = "2.0.0", default-features = false, features = ["std"] }

1
benches/executor.rs
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@ -1,3 +1,4 @@
use std::future::Future;
use std::thread::available_parallelism;
use async_executor::Executor;

1
examples/priority.rs
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@ -1,5 +1,6 @@
//! An executor with task priorities.
use std::future::Future;
use std::thread;
use async_executor::{Executor, Task};

133
src/lib.rs
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@ -34,20 +34,19 @@
)]
use std::fmt;
use std::future::Future;
use std::marker::PhantomData;
use std::panic::{RefUnwindSafe, UnwindSafe};
use std::rc::Rc;
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::{Arc, Mutex, TryLockError};
use std::sync::{Arc, Mutex, RwLock, TryLockError};
use std::task::{Poll, Waker};
use async_lock::OnceCell;
use async_task::{Builder, Runnable};
use atomic_waker::AtomicWaker;
use concurrent_queue::ConcurrentQueue;
use futures_lite::{future, prelude::*};
use slab::Slab;
use thread_local::ThreadLocal;
#[doc(no_inline)]
pub use async_task::Task;
@ -267,23 +266,8 @@ impl<'a> Executor<'a> {
fn schedule(&self) -> impl Fn(Runnable) + Send + Sync + 'static {
let state = self.state().clone();
move |mut runnable| {
// If possible, push into the current local queue and notify the ticker.
if let Some(local) = state.local_queue.get() {
runnable = if let Err(err) = local.queue.push(runnable) {
err.into_inner()
} else {
// Wake up this thread if it's asleep, otherwise notify another
// thread to try to have the task stolen.
if let Some(waker) = local.waker.take() {
waker.wake();
} else {
state.notify();
}
return;
}
}
// If the local queue is full, fallback to pushing onto the global injector queue.
// TODO: If possible, push into the current local queue and notify the ticker.
move |runnable| {
state.queue.push(runnable).unwrap();
state.notify();
}
@ -526,16 +510,7 @@ struct State {
queue: ConcurrentQueue<Runnable>,
/// Local queues created by runners.
///
/// If possible, tasks are scheduled onto the local queue, and will only defer
/// to other global queue when they're full, or the task is being scheduled from
/// a thread without a runner.
///
/// Note: if a runner terminates and drains its local queue, any subsequent
/// spawn calls from the same thread will be added to the same queue, but won't
/// be executed until `Executor::run` is run on the thread again, or another
/// thread steals the task.
local_queue: ThreadLocal<LocalQueue>,
local_queues: RwLock<Vec<Arc<ConcurrentQueue<Runnable>>>>,
/// Set to `true` when a sleeping ticker is notified or no tickers are sleeping.
notified: AtomicBool,
@ -552,7 +527,7 @@ impl State {
fn new() -> State {
State {
queue: ConcurrentQueue::unbounded(),
local_queue: ThreadLocal::new(),
local_queues: RwLock::new(Vec::new()),
notified: AtomicBool::new(true),
sleepers: Mutex::new(Sleepers {
count: 0,
@ -679,12 +654,6 @@ impl Ticker<'_> {
///
/// Returns `false` if the ticker was already sleeping and unnotified.
fn sleep(&mut self, waker: &Waker) -> bool {
self.state
.local_queue
.get_or_default()
.waker
.register(waker);
let mut sleepers = self.state.sleepers.lock().unwrap();
match self.sleeping {
@ -723,14 +692,7 @@ impl Ticker<'_> {
/// Waits for the next runnable task to run.
async fn runnable(&mut self) -> Runnable {
self.runnable_with(|| {
self.state
.local_queue
.get()
.and_then(|local| local.queue.pop().ok())
.or_else(|| self.state.queue.pop().ok())
})
.await
self.runnable_with(|| self.state.queue.pop().ok()).await
}
/// Waits for the next runnable task to run, given a function that searches for a task.
@ -792,6 +754,9 @@ struct Runner<'a> {
/// Inner ticker.
ticker: Ticker<'a>,
/// The local queue.
local: Arc<ConcurrentQueue<Runnable>>,
/// Bumped every time a runnable task is found.
ticks: usize,
}
@ -802,34 +767,38 @@ impl Runner<'_> {
let runner = Runner {
state,
ticker: Ticker::new(state),
local: Arc::new(ConcurrentQueue::bounded(512)),
ticks: 0,
};
state
.local_queues
.write()
.unwrap()
.push(runner.local.clone());
runner
}
/// Waits for the next runnable task to run.
async fn runnable(&mut self, rng: &mut fastrand::Rng) -> Runnable {
let local = self.state.local_queue.get_or_default();
let runnable = self
.ticker
.runnable_with(|| {
// Try the local queue.
if let Ok(r) = local.queue.pop() {
if let Ok(r) = self.local.pop() {
return Some(r);
}
// Try stealing from the global queue.
if let Ok(r) = self.state.queue.pop() {
steal(&self.state.queue, &local.queue);
steal(&self.state.queue, &self.local);
return Some(r);
}
// Try stealing from other runners.
let local_queues = &self.state.local_queue;
let local_queues = self.state.local_queues.read().unwrap();
// Pick a random starting point in the iterator list and rotate the list.
let n = local_queues.iter().count();
let n = local_queues.len();
let start = rng.usize(..n);
let iter = local_queues
.iter()
@ -838,12 +807,12 @@ impl Runner<'_> {
.take(n);
// Remove this runner's local queue.
let iter = iter.filter(|other| !core::ptr::eq(*other, local));
let iter = iter.filter(|local| !Arc::ptr_eq(local, &self.local));
// Try stealing from each local queue in the list.
for other in iter {
steal(&other.queue, &local.queue);
if let Ok(r) = local.queue.pop() {
for local in iter {
steal(local, &self.local);
if let Ok(r) = self.local.pop() {
return Some(r);
}
}
@ -857,7 +826,7 @@ impl Runner<'_> {
if self.ticks % 64 == 0 {
// Steal tasks from the global queue to ensure fair task scheduling.
steal(&self.state.queue, &local.queue);
steal(&self.state.queue, &self.local);
}
runnable
@ -867,13 +836,15 @@ impl Runner<'_> {
impl Drop for Runner<'_> {
fn drop(&mut self) {
// Remove the local queue.
if let Some(local) = self.state.local_queue.get() {
// Re-schedule remaining tasks in the local queue.
for r in local.queue.try_iter() {
// Explicitly reschedule the runnable back onto the global
// queue to avoid rescheduling onto the local one.
self.state.queue.push(r).unwrap();
}
self.state
.local_queues
.write()
.unwrap()
.retain(|local| !Arc::ptr_eq(local, &self.local));
// Re-schedule remaining tasks in the local queue.
while let Ok(r) = self.local.pop() {
r.schedule();
}
}
}
@ -933,13 +904,18 @@ fn debug_executor(executor: &Executor<'_>, name: &str, f: &mut fmt::Formatter<'_
}
/// Debug wrapper for the local runners.
struct LocalRunners<'a>(&'a ThreadLocal<LocalQueue>);
struct LocalRunners<'a>(&'a RwLock<Vec<Arc<ConcurrentQueue<Runnable>>>>);
impl fmt::Debug for LocalRunners<'_> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_list()
.entries(self.0.iter().map(|local| local.queue.len()))
.finish()
match self.0.try_read() {
Ok(lock) => f
.debug_list()
.entries(lock.iter().map(|queue| queue.len()))
.finish(),
Err(TryLockError::WouldBlock) => f.write_str("<locked>"),
Err(TryLockError::Poisoned(_)) => f.write_str("<poisoned>"),
}
}
}
@ -959,32 +935,11 @@ fn debug_executor(executor: &Executor<'_>, name: &str, f: &mut fmt::Formatter<'_
f.debug_struct(name)
.field("active", &ActiveTasks(&state.active))
.field("global_tasks", &state.queue.len())
.field("local_runners", &LocalRunners(&state.local_queue))
.field("local_runners", &LocalRunners(&state.local_queues))
.field("sleepers", &SleepCount(&state.sleepers))
.finish()
}
/// A queue local to each thread.
///
/// It's Default implementation is used for initializing each
/// thread's queue via `ThreadLocal::get_or_default`.
///
/// The local queue *must* be flushed, and all pending runnables
/// rescheduled onto the global queue when a runner is dropped.
struct LocalQueue {
queue: ConcurrentQueue<Runnable>,
waker: AtomicWaker,
}
impl Default for LocalQueue {
fn default() -> Self {
Self {
queue: ConcurrentQueue::bounded(512),
waker: AtomicWaker::new(),
}
}
}
/// Runs a closure when dropped.
struct CallOnDrop<F: FnMut()>(F);