Jeff Vander Stoep | bf37273 | 2021-02-18 09:39:46 +0100 | [diff] [blame] | 1 | //! Futures task based helpers |
| 2 | |
| 3 | #![allow(clippy::mutex_atomic)] |
| 4 | |
| 5 | use std::future::Future; |
| 6 | use std::mem; |
| 7 | use std::ops; |
| 8 | use std::pin::Pin; |
| 9 | use std::sync::{Arc, Condvar, Mutex}; |
| 10 | use std::task::{Context, Poll, RawWaker, RawWakerVTable, Waker}; |
| 11 | |
| 12 | use tokio_stream::Stream; |
| 13 | |
| 14 | /// TODO: dox |
| 15 | pub fn spawn<T>(task: T) -> Spawn<T> { |
| 16 | Spawn { |
| 17 | task: MockTask::new(), |
| 18 | future: Box::pin(task), |
| 19 | } |
| 20 | } |
| 21 | |
| 22 | /// Future spawned on a mock task |
| 23 | #[derive(Debug)] |
| 24 | pub struct Spawn<T> { |
| 25 | task: MockTask, |
| 26 | future: Pin<Box<T>>, |
| 27 | } |
| 28 | |
| 29 | /// Mock task |
| 30 | /// |
| 31 | /// A mock task is able to intercept and track wake notifications. |
| 32 | #[derive(Debug, Clone)] |
| 33 | struct MockTask { |
| 34 | waker: Arc<ThreadWaker>, |
| 35 | } |
| 36 | |
| 37 | #[derive(Debug)] |
| 38 | struct ThreadWaker { |
| 39 | state: Mutex<usize>, |
| 40 | condvar: Condvar, |
| 41 | } |
| 42 | |
| 43 | const IDLE: usize = 0; |
| 44 | const WAKE: usize = 1; |
| 45 | const SLEEP: usize = 2; |
| 46 | |
| 47 | impl<T> Spawn<T> { |
| 48 | /// Consumes `self` returning the inner value |
| 49 | pub fn into_inner(self) -> T |
| 50 | where |
| 51 | T: Unpin, |
| 52 | { |
| 53 | *Pin::into_inner(self.future) |
| 54 | } |
| 55 | |
| 56 | /// Returns `true` if the inner future has received a wake notification |
| 57 | /// since the last call to `enter`. |
| 58 | pub fn is_woken(&self) -> bool { |
| 59 | self.task.is_woken() |
| 60 | } |
| 61 | |
| 62 | /// Returns the number of references to the task waker |
| 63 | /// |
| 64 | /// The task itself holds a reference. The return value will never be zero. |
| 65 | pub fn waker_ref_count(&self) -> usize { |
| 66 | self.task.waker_ref_count() |
| 67 | } |
| 68 | |
| 69 | /// Enter the task context |
| 70 | pub fn enter<F, R>(&mut self, f: F) -> R |
| 71 | where |
| 72 | F: FnOnce(&mut Context<'_>, Pin<&mut T>) -> R, |
| 73 | { |
| 74 | let fut = self.future.as_mut(); |
| 75 | self.task.enter(|cx| f(cx, fut)) |
| 76 | } |
| 77 | } |
| 78 | |
| 79 | impl<T: Unpin> ops::Deref for Spawn<T> { |
| 80 | type Target = T; |
| 81 | |
| 82 | fn deref(&self) -> &T { |
| 83 | &self.future |
| 84 | } |
| 85 | } |
| 86 | |
| 87 | impl<T: Unpin> ops::DerefMut for Spawn<T> { |
| 88 | fn deref_mut(&mut self) -> &mut T { |
| 89 | &mut self.future |
| 90 | } |
| 91 | } |
| 92 | |
| 93 | impl<T: Future> Spawn<T> { |
| 94 | /// Polls a future |
| 95 | pub fn poll(&mut self) -> Poll<T::Output> { |
| 96 | let fut = self.future.as_mut(); |
| 97 | self.task.enter(|cx| fut.poll(cx)) |
| 98 | } |
| 99 | } |
| 100 | |
| 101 | impl<T: Stream> Spawn<T> { |
| 102 | /// Polls a stream |
| 103 | pub fn poll_next(&mut self) -> Poll<Option<T::Item>> { |
| 104 | let stream = self.future.as_mut(); |
| 105 | self.task.enter(|cx| stream.poll_next(cx)) |
| 106 | } |
| 107 | } |
| 108 | |
| 109 | impl<T: Future> Future for Spawn<T> { |
| 110 | type Output = T::Output; |
| 111 | |
| 112 | fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { |
| 113 | self.future.as_mut().poll(cx) |
| 114 | } |
| 115 | } |
| 116 | |
| 117 | impl<T: Stream> Stream for Spawn<T> { |
| 118 | type Item = T::Item; |
| 119 | |
| 120 | fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> { |
| 121 | self.future.as_mut().poll_next(cx) |
| 122 | } |
| 123 | } |
| 124 | |
| 125 | impl MockTask { |
| 126 | /// Creates new mock task |
| 127 | fn new() -> Self { |
| 128 | MockTask { |
| 129 | waker: Arc::new(ThreadWaker::new()), |
| 130 | } |
| 131 | } |
| 132 | |
| 133 | /// Runs a closure from the context of the task. |
| 134 | /// |
| 135 | /// Any wake notifications resulting from the execution of the closure are |
| 136 | /// tracked. |
| 137 | fn enter<F, R>(&mut self, f: F) -> R |
| 138 | where |
| 139 | F: FnOnce(&mut Context<'_>) -> R, |
| 140 | { |
| 141 | self.waker.clear(); |
| 142 | let waker = self.waker(); |
| 143 | let mut cx = Context::from_waker(&waker); |
| 144 | |
| 145 | f(&mut cx) |
| 146 | } |
| 147 | |
| 148 | /// Returns `true` if the inner future has received a wake notification |
| 149 | /// since the last call to `enter`. |
| 150 | fn is_woken(&self) -> bool { |
| 151 | self.waker.is_woken() |
| 152 | } |
| 153 | |
| 154 | /// Returns the number of references to the task waker |
| 155 | /// |
| 156 | /// The task itself holds a reference. The return value will never be zero. |
| 157 | fn waker_ref_count(&self) -> usize { |
| 158 | Arc::strong_count(&self.waker) |
| 159 | } |
| 160 | |
| 161 | fn waker(&self) -> Waker { |
| 162 | unsafe { |
| 163 | let raw = to_raw(self.waker.clone()); |
| 164 | Waker::from_raw(raw) |
| 165 | } |
| 166 | } |
| 167 | } |
| 168 | |
| 169 | impl Default for MockTask { |
| 170 | fn default() -> Self { |
| 171 | Self::new() |
| 172 | } |
| 173 | } |
| 174 | |
| 175 | impl ThreadWaker { |
| 176 | fn new() -> Self { |
| 177 | ThreadWaker { |
| 178 | state: Mutex::new(IDLE), |
| 179 | condvar: Condvar::new(), |
| 180 | } |
| 181 | } |
| 182 | |
| 183 | /// Clears any previously received wakes, avoiding potential spurrious |
| 184 | /// wake notifications. This should only be called immediately before running the |
| 185 | /// task. |
| 186 | fn clear(&self) { |
| 187 | *self.state.lock().unwrap() = IDLE; |
| 188 | } |
| 189 | |
| 190 | fn is_woken(&self) -> bool { |
| 191 | match *self.state.lock().unwrap() { |
| 192 | IDLE => false, |
| 193 | WAKE => true, |
| 194 | _ => unreachable!(), |
| 195 | } |
| 196 | } |
| 197 | |
| 198 | fn wake(&self) { |
| 199 | // First, try transitioning from IDLE -> NOTIFY, this does not require a lock. |
| 200 | let mut state = self.state.lock().unwrap(); |
| 201 | let prev = *state; |
| 202 | |
| 203 | if prev == WAKE { |
| 204 | return; |
| 205 | } |
| 206 | |
| 207 | *state = WAKE; |
| 208 | |
| 209 | if prev == IDLE { |
| 210 | return; |
| 211 | } |
| 212 | |
| 213 | // The other half is sleeping, so we wake it up. |
| 214 | assert_eq!(prev, SLEEP); |
| 215 | self.condvar.notify_one(); |
| 216 | } |
| 217 | } |
| 218 | |
| 219 | static VTABLE: RawWakerVTable = RawWakerVTable::new(clone, wake, wake_by_ref, drop_waker); |
| 220 | |
| 221 | unsafe fn to_raw(waker: Arc<ThreadWaker>) -> RawWaker { |
| 222 | RawWaker::new(Arc::into_raw(waker) as *const (), &VTABLE) |
| 223 | } |
| 224 | |
| 225 | unsafe fn from_raw(raw: *const ()) -> Arc<ThreadWaker> { |
| 226 | Arc::from_raw(raw as *const ThreadWaker) |
| 227 | } |
| 228 | |
| 229 | unsafe fn clone(raw: *const ()) -> RawWaker { |
| 230 | let waker = from_raw(raw); |
| 231 | |
| 232 | // Increment the ref count |
| 233 | mem::forget(waker.clone()); |
| 234 | |
| 235 | to_raw(waker) |
| 236 | } |
| 237 | |
| 238 | unsafe fn wake(raw: *const ()) { |
| 239 | let waker = from_raw(raw); |
| 240 | waker.wake(); |
| 241 | } |
| 242 | |
| 243 | unsafe fn wake_by_ref(raw: *const ()) { |
| 244 | let waker = from_raw(raw); |
| 245 | waker.wake(); |
| 246 | |
| 247 | // We don't actually own a reference to the unparker |
| 248 | mem::forget(waker); |
| 249 | } |
| 250 | |
| 251 | unsafe fn drop_waker(raw: *const ()) { |
| 252 | let _ = from_raw(raw); |
| 253 | } |