1use anyhow::{anyhow, Result};
2use async_task::Runnable;
3use backtrace::{Backtrace, BacktraceFmt, BytesOrWideString};
4use parking_lot::Mutex;
5use postage::{barrier, prelude::Stream as _};
6use rand::prelude::*;
7use smol::{channel, prelude::*, Executor, Timer};
8use std::{
9 any::Any,
10 fmt::{self, Debug},
11 marker::PhantomData,
12 mem,
13 ops::RangeInclusive,
14 pin::Pin,
15 rc::Rc,
16 sync::{
17 atomic::{AtomicBool, Ordering::SeqCst},
18 Arc,
19 },
20 task::{Context, Poll},
21 thread,
22 time::{Duration, Instant},
23};
24use waker_fn::waker_fn;
25
26use crate::{
27 platform::{self, Dispatcher},
28 util,
29};
30
31pub enum Foreground {
32 Platform {
33 dispatcher: Arc<dyn platform::Dispatcher>,
34 _not_send_or_sync: PhantomData<Rc<()>>,
35 },
36 Test(smol::LocalExecutor<'static>),
37 Deterministic(Arc<Deterministic>),
38}
39
40pub enum Background {
41 Deterministic {
42 executor: Arc<Deterministic>,
43 },
44 Production {
45 executor: Arc<smol::Executor<'static>>,
46 _stop: channel::Sender<()>,
47 },
48}
49
50type AnyLocalFuture = Pin<Box<dyn 'static + Future<Output = Box<dyn Any + 'static>>>>;
51type AnyFuture = Pin<Box<dyn 'static + Send + Future<Output = Box<dyn Any + Send + 'static>>>>;
52type AnyTask = async_task::Task<Box<dyn Any + Send + 'static>>;
53type AnyLocalTask = async_task::Task<Box<dyn Any + 'static>>;
54
55#[must_use]
56pub enum Task<T> {
57 Ready(Option<T>),
58 Local {
59 any_task: AnyLocalTask,
60 result_type: PhantomData<T>,
61 },
62 Send {
63 any_task: AnyTask,
64 result_type: PhantomData<T>,
65 },
66}
67
68unsafe impl<T: Send> Send for Task<T> {}
69
70struct DeterministicState {
71 rng: StdRng,
72 seed: u64,
73 scheduled_from_foreground: Vec<(Runnable, Backtrace)>,
74 scheduled_from_background: Vec<(Runnable, Backtrace)>,
75 spawned_from_foreground: Vec<(Runnable, Backtrace)>,
76 forbid_parking: bool,
77 block_on_ticks: RangeInclusive<usize>,
78 now: Instant,
79 pending_timers: Vec<(Instant, barrier::Sender)>,
80}
81
82pub struct Deterministic {
83 state: Arc<Mutex<DeterministicState>>,
84 parker: Mutex<parking::Parker>,
85}
86
87impl Deterministic {
88 fn new(seed: u64) -> Self {
89 Self {
90 state: Arc::new(Mutex::new(DeterministicState {
91 rng: StdRng::seed_from_u64(seed),
92 seed,
93 scheduled_from_foreground: Default::default(),
94 scheduled_from_background: Default::default(),
95 spawned_from_foreground: Default::default(),
96 forbid_parking: false,
97 block_on_ticks: 0..=1000,
98 now: Instant::now(),
99 pending_timers: Default::default(),
100 })),
101 parker: Default::default(),
102 }
103 }
104
105 fn spawn_from_foreground(&self, future: AnyLocalFuture) -> AnyLocalTask {
106 let backtrace = Backtrace::new_unresolved();
107 let scheduled_once = AtomicBool::new(false);
108 let state = self.state.clone();
109 let unparker = self.parker.lock().unparker();
110 let (runnable, task) = async_task::spawn_local(future, move |runnable| {
111 let mut state = state.lock();
112 let backtrace = backtrace.clone();
113 if scheduled_once.fetch_or(true, SeqCst) {
114 state.scheduled_from_foreground.push((runnable, backtrace));
115 } else {
116 state.spawned_from_foreground.push((runnable, backtrace));
117 }
118 unparker.unpark();
119 });
120 runnable.schedule();
121 task
122 }
123
124 fn spawn(&self, future: AnyFuture) -> AnyTask {
125 let backtrace = Backtrace::new_unresolved();
126 let state = self.state.clone();
127 let unparker = self.parker.lock().unparker();
128 let (runnable, task) = async_task::spawn(future, move |runnable| {
129 let mut state = state.lock();
130 state
131 .scheduled_from_background
132 .push((runnable, backtrace.clone()));
133 unparker.unpark();
134 });
135 runnable.schedule();
136 task
137 }
138
139 fn run(&self, mut future: AnyLocalFuture) -> Box<dyn Any> {
140 let woken = Arc::new(AtomicBool::new(false));
141 loop {
142 if let Some(result) = self.run_internal(woken.clone(), &mut future) {
143 return result;
144 }
145
146 if !woken.load(SeqCst) && self.state.lock().forbid_parking {
147 panic!("deterministic executor parked after a call to forbid_parking");
148 }
149
150 woken.store(false, SeqCst);
151 self.parker.lock().park();
152 }
153 }
154
155 fn run_until_parked(&self) {
156 let woken = Arc::new(AtomicBool::new(false));
157 let mut future = any_local_future(std::future::pending::<()>());
158 self.run_internal(woken, &mut future);
159 }
160
161 fn run_internal(
162 &self,
163 woken: Arc<AtomicBool>,
164 future: &mut AnyLocalFuture,
165 ) -> Option<Box<dyn Any>> {
166 let unparker = self.parker.lock().unparker();
167 let waker = waker_fn(move || {
168 woken.store(true, SeqCst);
169 unparker.unpark();
170 });
171
172 let mut cx = Context::from_waker(&waker);
173 let mut trace = Trace::default();
174 loop {
175 let mut state = self.state.lock();
176 let runnable_count = state.scheduled_from_foreground.len()
177 + state.scheduled_from_background.len()
178 + state.spawned_from_foreground.len();
179
180 let ix = state.rng.gen_range(0..=runnable_count);
181 if ix < state.scheduled_from_foreground.len() {
182 let (_, backtrace) = &state.scheduled_from_foreground[ix];
183 trace.record(&state, backtrace.clone());
184 let runnable = state.scheduled_from_foreground.remove(ix).0;
185 drop(state);
186 runnable.run();
187 } else if ix - state.scheduled_from_foreground.len()
188 < state.scheduled_from_background.len()
189 {
190 let ix = ix - state.scheduled_from_foreground.len();
191 let (_, backtrace) = &state.scheduled_from_background[ix];
192 trace.record(&state, backtrace.clone());
193 let runnable = state.scheduled_from_background.remove(ix).0;
194 drop(state);
195 runnable.run();
196 } else if ix < runnable_count {
197 let (_, backtrace) = &state.spawned_from_foreground[0];
198 trace.record(&state, backtrace.clone());
199 let runnable = state.spawned_from_foreground.remove(0).0;
200 drop(state);
201 runnable.run();
202 } else {
203 drop(state);
204 if let Poll::Ready(result) = future.poll(&mut cx) {
205 return Some(result);
206 }
207
208 let state = self.state.lock();
209 if state.scheduled_from_foreground.is_empty()
210 && state.scheduled_from_background.is_empty()
211 && state.spawned_from_foreground.is_empty()
212 {
213 return None;
214 }
215 }
216 }
217 }
218
219 fn block_on(&self, future: &mut AnyLocalFuture) -> Option<Box<dyn Any>> {
220 let unparker = self.parker.lock().unparker();
221 let waker = waker_fn(move || {
222 unparker.unpark();
223 });
224 let max_ticks = {
225 let mut state = self.state.lock();
226 let range = state.block_on_ticks.clone();
227 state.rng.gen_range(range)
228 };
229
230 let mut cx = Context::from_waker(&waker);
231 let mut trace = Trace::default();
232 for _ in 0..max_ticks {
233 let mut state = self.state.lock();
234 let runnable_count = state.scheduled_from_background.len();
235 let ix = state.rng.gen_range(0..=runnable_count);
236 if ix < state.scheduled_from_background.len() {
237 let (_, backtrace) = &state.scheduled_from_background[ix];
238 trace.record(&state, backtrace.clone());
239 let runnable = state.scheduled_from_background.remove(ix).0;
240 drop(state);
241 runnable.run();
242 } else {
243 drop(state);
244 if let Poll::Ready(result) = future.as_mut().poll(&mut cx) {
245 return Some(result);
246 }
247 let state = self.state.lock();
248 if state.scheduled_from_background.is_empty() {
249 if state.forbid_parking {
250 panic!("deterministic executor parked after a call to forbid_parking");
251 }
252 drop(state);
253 self.parker.lock().park();
254 }
255
256 continue;
257 }
258 }
259
260 None
261 }
262}
263
264#[derive(Default)]
265struct Trace {
266 executed: Vec<Backtrace>,
267 scheduled: Vec<Vec<Backtrace>>,
268 spawned_from_foreground: Vec<Vec<Backtrace>>,
269}
270
271impl Trace {
272 fn record(&mut self, state: &DeterministicState, executed: Backtrace) {
273 self.scheduled.push(
274 state
275 .scheduled_from_foreground
276 .iter()
277 .map(|(_, backtrace)| backtrace.clone())
278 .collect(),
279 );
280 self.spawned_from_foreground.push(
281 state
282 .spawned_from_foreground
283 .iter()
284 .map(|(_, backtrace)| backtrace.clone())
285 .collect(),
286 );
287 self.executed.push(executed);
288 }
289
290 fn resolve(&mut self) {
291 for backtrace in &mut self.executed {
292 backtrace.resolve();
293 }
294
295 for backtraces in &mut self.scheduled {
296 for backtrace in backtraces {
297 backtrace.resolve();
298 }
299 }
300
301 for backtraces in &mut self.spawned_from_foreground {
302 for backtrace in backtraces {
303 backtrace.resolve();
304 }
305 }
306 }
307}
308
309impl Debug for Trace {
310 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
311 struct FirstCwdFrameInBacktrace<'a>(&'a Backtrace);
312
313 impl<'a> Debug for FirstCwdFrameInBacktrace<'a> {
314 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> std::fmt::Result {
315 let cwd = std::env::current_dir().unwrap();
316 let mut print_path = |fmt: &mut fmt::Formatter<'_>, path: BytesOrWideString<'_>| {
317 fmt::Display::fmt(&path, fmt)
318 };
319 let mut fmt = BacktraceFmt::new(f, backtrace::PrintFmt::Full, &mut print_path);
320 for frame in self.0.frames() {
321 let mut formatted_frame = fmt.frame();
322 if frame
323 .symbols()
324 .iter()
325 .any(|s| s.filename().map_or(false, |f| f.starts_with(&cwd)))
326 {
327 formatted_frame.backtrace_frame(frame)?;
328 break;
329 }
330 }
331 fmt.finish()
332 }
333 }
334
335 for ((backtrace, scheduled), spawned_from_foreground) in self
336 .executed
337 .iter()
338 .zip(&self.scheduled)
339 .zip(&self.spawned_from_foreground)
340 {
341 writeln!(f, "Scheduled")?;
342 for backtrace in scheduled {
343 writeln!(f, "- {:?}", FirstCwdFrameInBacktrace(backtrace))?;
344 }
345 if scheduled.is_empty() {
346 writeln!(f, "None")?;
347 }
348 writeln!(f, "==========")?;
349
350 writeln!(f, "Spawned from foreground")?;
351 for backtrace in spawned_from_foreground {
352 writeln!(f, "- {:?}", FirstCwdFrameInBacktrace(backtrace))?;
353 }
354 if spawned_from_foreground.is_empty() {
355 writeln!(f, "None")?;
356 }
357 writeln!(f, "==========")?;
358
359 writeln!(f, "Run: {:?}", FirstCwdFrameInBacktrace(backtrace))?;
360 writeln!(f, "+++++++++++++++++++")?;
361 }
362
363 Ok(())
364 }
365}
366
367impl Drop for Trace {
368 fn drop(&mut self) {
369 let trace_on_panic = if let Ok(trace_on_panic) = std::env::var("EXECUTOR_TRACE_ON_PANIC") {
370 trace_on_panic == "1" || trace_on_panic == "true"
371 } else {
372 false
373 };
374 let trace_always = if let Ok(trace_always) = std::env::var("EXECUTOR_TRACE_ALWAYS") {
375 trace_always == "1" || trace_always == "true"
376 } else {
377 false
378 };
379
380 if trace_always || (trace_on_panic && thread::panicking()) {
381 self.resolve();
382 dbg!(self);
383 }
384 }
385}
386
387impl Foreground {
388 pub fn platform(dispatcher: Arc<dyn platform::Dispatcher>) -> Result<Self> {
389 if dispatcher.is_main_thread() {
390 Ok(Self::Platform {
391 dispatcher,
392 _not_send_or_sync: PhantomData,
393 })
394 } else {
395 Err(anyhow!("must be constructed on main thread"))
396 }
397 }
398
399 pub fn test() -> Self {
400 Self::Test(smol::LocalExecutor::new())
401 }
402
403 pub fn spawn<T: 'static>(&self, future: impl Future<Output = T> + 'static) -> Task<T> {
404 let future = any_local_future(future);
405 let any_task = match self {
406 Self::Deterministic(executor) => executor.spawn_from_foreground(future),
407 Self::Platform { dispatcher, .. } => {
408 fn spawn_inner(
409 future: AnyLocalFuture,
410 dispatcher: &Arc<dyn Dispatcher>,
411 ) -> AnyLocalTask {
412 let dispatcher = dispatcher.clone();
413 let schedule =
414 move |runnable: Runnable| dispatcher.run_on_main_thread(runnable);
415 let (runnable, task) = async_task::spawn_local(future, schedule);
416 runnable.schedule();
417 task
418 }
419 spawn_inner(future, dispatcher)
420 }
421 Self::Test(executor) => executor.spawn(future),
422 };
423 Task::local(any_task)
424 }
425
426 pub fn run<T: 'static>(&self, future: impl 'static + Future<Output = T>) -> T {
427 let future = any_local_future(future);
428 let any_value = match self {
429 Self::Deterministic(executor) => executor.run(future),
430 Self::Platform { .. } => panic!("you can't call run on a platform foreground executor"),
431 Self::Test(executor) => smol::block_on(executor.run(future)),
432 };
433 *any_value.downcast().unwrap()
434 }
435
436 pub fn forbid_parking(&self) {
437 match self {
438 Self::Deterministic(executor) => {
439 let mut state = executor.state.lock();
440 state.forbid_parking = true;
441 state.rng = StdRng::seed_from_u64(state.seed);
442 }
443 _ => panic!("this method can only be called on a deterministic executor"),
444 }
445 }
446
447 pub async fn timer(&self, duration: Duration) {
448 match self {
449 Self::Deterministic(executor) => {
450 let (tx, mut rx) = barrier::channel();
451 {
452 let mut state = executor.state.lock();
453 let wakeup_at = state.now + duration;
454 state.pending_timers.push((wakeup_at, tx));
455 }
456 rx.recv().await;
457 }
458 _ => {
459 Timer::after(duration).await;
460 }
461 }
462 }
463
464 pub fn advance_clock(&self, duration: Duration) {
465 match self {
466 Self::Deterministic(executor) => {
467 executor.run_until_parked();
468
469 let mut state = executor.state.lock();
470 state.now += duration;
471 let now = state.now;
472 let mut pending_timers = mem::take(&mut state.pending_timers);
473 drop(state);
474
475 pending_timers.retain(|(wakeup, _)| *wakeup > now);
476 executor.state.lock().pending_timers.extend(pending_timers);
477 }
478 _ => panic!("this method can only be called on a deterministic executor"),
479 }
480 }
481
482 pub fn set_block_on_ticks(&self, range: RangeInclusive<usize>) {
483 match self {
484 Self::Deterministic(executor) => executor.state.lock().block_on_ticks = range,
485 _ => panic!("this method can only be called on a deterministic executor"),
486 }
487 }
488}
489
490impl Background {
491 pub fn new() -> Self {
492 let executor = Arc::new(Executor::new());
493 let stop = channel::unbounded::<()>();
494
495 for i in 0..2 * num_cpus::get() {
496 let executor = executor.clone();
497 let stop = stop.1.clone();
498 thread::Builder::new()
499 .name(format!("background-executor-{}", i))
500 .spawn(move || smol::block_on(executor.run(stop.recv())))
501 .unwrap();
502 }
503
504 Self::Production {
505 executor,
506 _stop: stop.0,
507 }
508 }
509
510 pub fn num_cpus(&self) -> usize {
511 num_cpus::get()
512 }
513
514 pub fn spawn<T, F>(&self, future: F) -> Task<T>
515 where
516 T: 'static + Send,
517 F: Send + Future<Output = T> + 'static,
518 {
519 let future = any_future(future);
520 let any_task = match self {
521 Self::Production { executor, .. } => executor.spawn(future),
522 Self::Deterministic { executor, .. } => executor.spawn(future),
523 };
524 Task::send(any_task)
525 }
526
527 pub fn block_with_timeout<F, T>(
528 &self,
529 timeout: Duration,
530 future: F,
531 ) -> Result<T, impl Future<Output = T>>
532 where
533 T: 'static,
534 F: 'static + Unpin + Future<Output = T>,
535 {
536 let mut future = any_local_future(future);
537 if !timeout.is_zero() {
538 let output = match self {
539 Self::Production { .. } => smol::block_on(util::timeout(timeout, &mut future)).ok(),
540 Self::Deterministic { executor, .. } => executor.block_on(&mut future),
541 };
542 if let Some(output) = output {
543 return Ok(*output.downcast().unwrap());
544 }
545 }
546 Err(async { *future.await.downcast().unwrap() })
547 }
548
549 pub async fn scoped<'scope, F>(&self, scheduler: F)
550 where
551 F: FnOnce(&mut Scope<'scope>),
552 {
553 let mut scope = Scope {
554 futures: Default::default(),
555 _phantom: PhantomData,
556 };
557 (scheduler)(&mut scope);
558 let spawned = scope
559 .futures
560 .into_iter()
561 .map(|f| self.spawn(f))
562 .collect::<Vec<_>>();
563 for task in spawned {
564 task.await;
565 }
566 }
567}
568
569pub struct Scope<'a> {
570 futures: Vec<Pin<Box<dyn Future<Output = ()> + Send + 'static>>>,
571 _phantom: PhantomData<&'a ()>,
572}
573
574impl<'a> Scope<'a> {
575 pub fn spawn<F>(&mut self, f: F)
576 where
577 F: Future<Output = ()> + Send + 'a,
578 {
579 let f = unsafe {
580 mem::transmute::<
581 Pin<Box<dyn Future<Output = ()> + Send + 'a>>,
582 Pin<Box<dyn Future<Output = ()> + Send + 'static>>,
583 >(Box::pin(f))
584 };
585 self.futures.push(f);
586 }
587}
588
589pub fn deterministic(seed: u64) -> (Rc<Foreground>, Arc<Background>) {
590 let executor = Arc::new(Deterministic::new(seed));
591 (
592 Rc::new(Foreground::Deterministic(executor.clone())),
593 Arc::new(Background::Deterministic { executor }),
594 )
595}
596
597impl<T> Task<T> {
598 pub fn ready(value: T) -> Self {
599 Self::Ready(Some(value))
600 }
601
602 fn local(any_task: AnyLocalTask) -> Self {
603 Self::Local {
604 any_task,
605 result_type: PhantomData,
606 }
607 }
608
609 pub fn detach(self) {
610 match self {
611 Task::Ready(_) => {}
612 Task::Local { any_task, .. } => any_task.detach(),
613 Task::Send { any_task, .. } => any_task.detach(),
614 }
615 }
616}
617
618impl<T: Send> Task<T> {
619 fn send(any_task: AnyTask) -> Self {
620 Self::Send {
621 any_task,
622 result_type: PhantomData,
623 }
624 }
625}
626
627impl<T: fmt::Debug> fmt::Debug for Task<T> {
628 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
629 match self {
630 Task::Ready(value) => value.fmt(f),
631 Task::Local { any_task, .. } => any_task.fmt(f),
632 Task::Send { any_task, .. } => any_task.fmt(f),
633 }
634 }
635}
636
637impl<T: 'static> Future for Task<T> {
638 type Output = T;
639
640 fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
641 match unsafe { self.get_unchecked_mut() } {
642 Task::Ready(value) => Poll::Ready(value.take().unwrap()),
643 Task::Local { any_task, .. } => {
644 any_task.poll(cx).map(|value| *value.downcast().unwrap())
645 }
646 Task::Send { any_task, .. } => {
647 any_task.poll(cx).map(|value| *value.downcast().unwrap())
648 }
649 }
650 }
651}
652
653fn any_future<T, F>(future: F) -> AnyFuture
654where
655 T: 'static + Send,
656 F: Future<Output = T> + Send + 'static,
657{
658 async { Box::new(future.await) as Box<dyn Any + Send> }.boxed()
659}
660
661fn any_local_future<T, F>(future: F) -> AnyLocalFuture
662where
663 T: 'static,
664 F: Future<Output = T> + 'static,
665{
666 async { Box::new(future.await) as Box<dyn Any> }.boxed_local()
667}