_ Git - rust-lightning/blob - lightning/src/util/wakers.rs

   1 // This file is Copyright its original authors, visible in version control
   2 // history.
   3 //
   4 // This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
   5 // or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
   7 // You may not use this file except in accordance with one or both of these
   8 // licenses.
   9
  10 //! Utilities which allow users to block on some future notification from LDK. These are
  11 //! specifically used by [`ChannelManager`] to allow waiting until the [`ChannelManager`] needs to
  12 //! be re-persisted.
  13 //!
  14 //! [`ChannelManager`]: crate::ln::channelmanager::ChannelManager
  15
  16 use alloc::sync::Arc;
  17 use core::mem;
  18 use crate::sync::{Condvar, Mutex, MutexGuard};
  19
  20 use crate::prelude::*;
  21
  22 #[cfg(any(test, feature = "std"))]
  23 use std::time::{Duration, Instant};
  24
  25 use core::future::Future as StdFuture;
  26 use core::task::{Context, Poll};
  27 use core::pin::Pin;
  28
  29
  30 /// Used to signal to one of many waiters that the condition they're waiting on has happened.
  31 pub(crate) struct Notifier {
  32         notify_pending: Mutex<(bool, Option<Arc<Mutex<FutureState>>>)>,
  33         condvar: Condvar,
  34 }
  35
  36 macro_rules! check_woken {
  37         ($guard: expr, $retval: expr) => { {
  38                 if $guard.0 {
  39                         $guard.0 = false;
  40                         if $guard.1.as_ref().map(|l| l.lock().unwrap().complete).unwrap_or(false) {
  41                                 // If we're about to return as woken, and the future state is marked complete, wipe
  42                                 // the future state and let the next future wait until we get a new notify.
  43                                 $guard.1.take();
  44                         }
  45                         return $retval;
  46                 }
  47         } }
  48 }
  49
  50 impl Notifier {
  51         pub(crate) fn new() -> Self {
  52                 Self {
  53                         notify_pending: Mutex::new((false, None)),
  54                         condvar: Condvar::new(),
  55                 }
  56         }
  57
  58         fn propagate_future_state_to_notify_flag(&self) -> MutexGuard<(bool, Option<Arc<Mutex<FutureState>>>)> {
  59                 let mut lock = self.notify_pending.lock().unwrap();
  60                 if let Some(existing_state) = &lock.1 {
  61                         if existing_state.lock().unwrap().callbacks_made {
  62                                 // If the existing `FutureState` has completed and actually made callbacks,
  63                                 // consider the notification flag to have been cleared and reset the future state.
  64                                 lock.1.take();
  65                                 lock.0 = false;
  66                         }
  67                 }
  68                 lock
  69         }
  70
  71         pub(crate) fn wait(&self) {
  72                 loop {
  73                         let mut guard = self.propagate_future_state_to_notify_flag();
  74                         check_woken!(guard, ());
  75                         guard = self.condvar.wait(guard).unwrap();
  76                         check_woken!(guard, ());
  77                 }
  78         }
  79
  80         #[cfg(any(test, feature = "std"))]
  81         pub(crate) fn wait_timeout(&self, max_wait: Duration) -> bool {
  82                 let current_time = Instant::now();
  83                 loop {
  84                         let mut guard = self.propagate_future_state_to_notify_flag();
  85                         check_woken!(guard, true);
  86                         guard = self.condvar.wait_timeout(guard, max_wait).unwrap().0;
  87                         check_woken!(guard, true);
  88                         // Due to spurious wakeups that can happen on `wait_timeout`, here we need to check if the
  89                         // desired wait time has actually passed, and if not then restart the loop with a reduced wait
  90                         // time. Note that this logic can be highly simplified through the use of
  91                         // `Condvar::wait_while` and `Condvar::wait_timeout_while`, if and when our MSRV is raised to
  92                         // 1.42.0.
  93                         let elapsed = current_time.elapsed();
  94                         if elapsed >= max_wait {
  95                                 return false;
  96                         }
  97                         match max_wait.checked_sub(elapsed) {
  98                                 None => return false,
  99                                 Some(_) => continue
 100                         }
 101                 }
 102         }
 103
 104         /// Wake waiters, tracking that wake needs to occur even if there are currently no waiters.
 105         pub(crate) fn notify(&self) {
 106                 let mut lock = self.notify_pending.lock().unwrap();
 107                 if let Some(future_state) = &lock.1 {
 108                         future_state.lock().unwrap().complete();
 109                 }
 110                 lock.0 = true;
 111                 mem::drop(lock);
 112                 self.condvar.notify_all();
 113         }
 114
 115         /// Gets a [`Future`] that will get woken up with any waiters
 116         pub(crate) fn get_future(&self) -> Future {
 117                 let mut lock = self.propagate_future_state_to_notify_flag();
 118                 if let Some(existing_state) = &lock.1 {
 119                         Future { state: Arc::clone(&existing_state) }
 120                 } else {
 121                         let state = Arc::new(Mutex::new(FutureState {
 122                                 callbacks: Vec::new(),
 123                                 complete: lock.0,
 124                                 callbacks_made: false,
 125                         }));
 126                         lock.1 = Some(Arc::clone(&state));
 127                         Future { state }
 128                 }
 129         }
 130
 131         #[cfg(any(test, feature = "_test_utils"))]
 132         pub fn notify_pending(&self) -> bool {
 133                 self.notify_pending.lock().unwrap().0
 134         }
 135 }
 136
 137 /// A callback which is called when a [`Future`] completes.
 138 ///
 139 /// Note that this MUST NOT call back into LDK directly, it must instead schedule actions to be
 140 /// taken later. Rust users should use the [`std::future::Future`] implementation for [`Future`]
 141 /// instead.
 142 ///
 143 /// Note that the [`std::future::Future`] implementation may only work for runtimes which schedule
 144 /// futures when they receive a wake, rather than immediately executing them.
 145 pub trait FutureCallback : Send {
 146         /// The method which is called.
 147         fn call(&self);
 148 }
 149
 150 impl<F: Fn() + Send> FutureCallback for F {
 151         fn call(&self) { (self)(); }
 152 }
 153
 154 pub(crate) struct FutureState {
 155         // When we're tracking whether a callback counts as having woken the user's code, we check the
 156         // first bool - set to false if we're just calling a Waker, and true if we're calling an actual
 157         // user-provided function.
 158         callbacks: Vec<(bool, Box<dyn FutureCallback>)>,
 159         complete: bool,
 160         callbacks_made: bool,
 161 }
 162
 163 impl FutureState {
 164         fn complete(&mut self) {
 165                 for (counts_as_call, callback) in self.callbacks.drain(..) {
 166                         callback.call();
 167                         self.callbacks_made |= counts_as_call;
 168                 }
 169                 self.complete = true;
 170         }
 171 }
 172
 173 /// A simple future which can complete once, and calls some callback(s) when it does so.
 174 pub struct Future {
 175         state: Arc<Mutex<FutureState>>,
 176 }
 177
 178 impl Future {
 179         /// Registers a callback to be called upon completion of this future. If the future has already
 180         /// completed, the callback will be called immediately.
 181         ///
 182         /// (C-not exported) use the bindings-only `register_callback_fn` instead
 183         pub fn register_callback(&self, callback: Box<dyn FutureCallback>) {
 184                 let mut state = self.state.lock().unwrap();
 185                 if state.complete {
 186                         state.callbacks_made = true;
 187                         mem::drop(state);
 188                         callback.call();
 189                 } else {
 190                         state.callbacks.push((true, callback));
 191                 }
 192         }
 193
 194         // C bindings don't (currently) know how to map `Box<dyn Trait>`, and while it could add the
 195         // following wrapper, doing it in the bindings is currently much more work than simply doing it
 196         // here.
 197         /// Registers a callback to be called upon completion of this future. If the future has already
 198         /// completed, the callback will be called immediately.
 199         #[cfg(c_bindings)]
 200         pub fn register_callback_fn<F: 'static + FutureCallback>(&self, callback: F) {
 201                 self.register_callback(Box::new(callback));
 202         }
 203 }
 204
 205 use core::task::Waker;
 206 struct StdWaker(pub Waker);
 207 impl FutureCallback for StdWaker {
 208         fn call(&self) { self.0.wake_by_ref() }
 209 }
 210
 211 /// (C-not exported) as Rust Futures aren't usable in language bindings.
 212 impl<'a> StdFuture for Future {
 213         type Output = ();
 214
 215         fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
 216                 let mut state = self.state.lock().unwrap();
 217                 if state.complete {
 218                         state.callbacks_made = true;
 219                         Poll::Ready(())
 220                 } else {
 221                         let waker = cx.waker().clone();
 222                         state.callbacks.push((false, Box::new(StdWaker(waker))));
 223                         Poll::Pending
 224                 }
 225         }
 226 }
 227
 228 #[cfg(test)]
 229 mod tests {
 230         use super::*;
 231         use core::sync::atomic::{AtomicBool, Ordering};
 232         use core::future::Future as FutureTrait;
 233         use core::task::{Context, Poll, RawWaker, RawWakerVTable, Waker};
 234
 235         #[test]
 236         fn notifier_pre_notified_future() {
 237                 // Previously, if we generated a future after a `Notifier` had been notified, the future
 238                 // would never complete. This tests this behavior, ensuring the future instead completes
 239                 // immediately.
 240                 let notifier = Notifier::new();
 241                 notifier.notify();
 242
 243                 let callback = Arc::new(AtomicBool::new(false));
 244                 let callback_ref = Arc::clone(&callback);
 245                 notifier.get_future().register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 246                 assert!(callback.load(Ordering::SeqCst));
 247         }
 248
 249         #[test]
 250         fn notifier_future_completes_wake() {
 251                 // Previously, if we were only using the `Future` interface to learn when a `Notifier` has
 252                 // been notified, we'd never mark the notifier as not-awaiting-notify. This caused the
 253                 // `lightning-background-processor` to persist in a tight loop.
 254                 let notifier = Notifier::new();
 255
 256                 // First check the simple case, ensuring if we get notified a new future isn't woken until
 257                 // a second `notify`.
 258                 let callback = Arc::new(AtomicBool::new(false));
 259                 let callback_ref = Arc::clone(&callback);
 260                 notifier.get_future().register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 261                 assert!(!callback.load(Ordering::SeqCst));
 262
 263                 notifier.notify();
 264                 assert!(callback.load(Ordering::SeqCst));
 265
 266                 let callback = Arc::new(AtomicBool::new(false));
 267                 let callback_ref = Arc::clone(&callback);
 268                 notifier.get_future().register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 269                 assert!(!callback.load(Ordering::SeqCst));
 270
 271                 notifier.notify();
 272                 assert!(callback.load(Ordering::SeqCst));
 273
 274                 // Then check the case where the future is fetched before the notification, but a callback
 275                 // is only registered after the `notify`, ensuring that it is still sufficient to ensure we
 276                 // don't get an instant-wake when we get a new future.
 277                 let future = notifier.get_future();
 278                 notifier.notify();
 279
 280                 let callback = Arc::new(AtomicBool::new(false));
 281                 let callback_ref = Arc::clone(&callback);
 282                 future.register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 283                 assert!(callback.load(Ordering::SeqCst));
 284
 285                 let callback = Arc::new(AtomicBool::new(false));
 286                 let callback_ref = Arc::clone(&callback);
 287                 notifier.get_future().register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 288                 assert!(!callback.load(Ordering::SeqCst));
 289         }
 290
 291         #[test]
 292         fn new_future_wipes_notify_bit() {
 293                 // Previously, if we were only using the `Future` interface to learn when a `Notifier` has
 294                 // been notified, we'd never mark the notifier as not-awaiting-notify if a `Future` is
 295                 // fetched after the notify bit has been set.
 296                 let notifier = Notifier::new();
 297                 notifier.notify();
 298
 299                 let callback = Arc::new(AtomicBool::new(false));
 300                 let callback_ref = Arc::clone(&callback);
 301                 notifier.get_future().register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 302                 assert!(callback.load(Ordering::SeqCst));
 303
 304                 let callback = Arc::new(AtomicBool::new(false));
 305                 let callback_ref = Arc::clone(&callback);
 306                 notifier.get_future().register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 307                 assert!(!callback.load(Ordering::SeqCst));
 308
 309                 notifier.notify();
 310                 assert!(callback.load(Ordering::SeqCst));
 311         }
 312
 313         #[cfg(feature = "std")]
 314         #[test]
 315         fn test_wait_timeout() {
 316                 use crate::sync::Arc;
 317                 use std::thread;
 318
 319                 let persistence_notifier = Arc::new(Notifier::new());
 320                 let thread_notifier = Arc::clone(&persistence_notifier);
 321
 322                 let exit_thread = Arc::new(AtomicBool::new(false));
 323                 let exit_thread_clone = exit_thread.clone();
 324                 thread::spawn(move || {
 325                         loop {
 326                                 let mut lock = thread_notifier.notify_pending.lock().unwrap();
 327                                 lock.0 = true;
 328                                 thread_notifier.condvar.notify_all();
 329
 330                                 if exit_thread_clone.load(Ordering::SeqCst) {
 331                                         break
 332                                 }
 333                         }
 334                 });
 335
 336                 // Check that we can block indefinitely until updates are available.
 337                 let _ = persistence_notifier.wait();
 338
 339                 // Check that the Notifier will return after the given duration if updates are
 340                 // available.
 341                 loop {
 342                         if persistence_notifier.wait_timeout(Duration::from_millis(100)) {
 343                                 break
 344                         }
 345                 }
 346
 347                 exit_thread.store(true, Ordering::SeqCst);
 348
 349                 // Check that the Notifier will return after the given duration even if no updates
 350                 // are available.
 351                 loop {
 352                         if !persistence_notifier.wait_timeout(Duration::from_millis(100)) {
 353                                 break
 354                         }
 355                 }
 356         }
 357
 358         #[test]
 359         fn test_future_callbacks() {
 360                 let future = Future {
 361                         state: Arc::new(Mutex::new(FutureState {
 362                                 callbacks: Vec::new(),
 363                                 complete: false,
 364                                 callbacks_made: false,
 365                         }))
 366                 };
 367                 let callback = Arc::new(AtomicBool::new(false));
 368                 let callback_ref = Arc::clone(&callback);
 369                 future.register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 370
 371                 assert!(!callback.load(Ordering::SeqCst));
 372                 future.state.lock().unwrap().complete();
 373                 assert!(callback.load(Ordering::SeqCst));
 374                 future.state.lock().unwrap().complete();
 375         }
 376
 377         #[test]
 378         fn test_pre_completed_future_callbacks() {
 379                 let future = Future {
 380                         state: Arc::new(Mutex::new(FutureState {
 381                                 callbacks: Vec::new(),
 382                                 complete: false,
 383                                 callbacks_made: false,
 384                         }))
 385                 };
 386                 future.state.lock().unwrap().complete();
 387
 388                 let callback = Arc::new(AtomicBool::new(false));
 389                 let callback_ref = Arc::clone(&callback);
 390                 future.register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 391
 392                 assert!(callback.load(Ordering::SeqCst));
 393                 assert!(future.state.lock().unwrap().callbacks.is_empty());
 394         }
 395
 396         // Rather annoyingly, there's no safe way in Rust std to construct a Waker despite it being
 397         // totally possible to construct from a trait implementation (though somewhat less effecient
 398         // compared to a raw VTable). Instead, we have to write out a lot of boilerplate to build a
 399         // waker, which we do here with a trivial Arc<AtomicBool> data element to track woke-ness.
 400         const WAKER_V_TABLE: RawWakerVTable = RawWakerVTable::new(waker_clone, wake, wake_by_ref, drop);
 401         unsafe fn wake_by_ref(ptr: *const ()) { let p = ptr as *const Arc<AtomicBool>; assert!(!(*p).fetch_or(true, Ordering::SeqCst)); }
 402         unsafe fn drop(ptr: *const ()) { let p = ptr as *mut Arc<AtomicBool>; let _freed = Box::from_raw(p); }
 403         unsafe fn wake(ptr: *const ()) { wake_by_ref(ptr); drop(ptr); }
 404         unsafe fn waker_clone(ptr: *const ()) -> RawWaker {
 405                 let p = ptr as *const Arc<AtomicBool>;
 406                 RawWaker::new(Box::into_raw(Box::new(Arc::clone(&*p))) as *const (), &WAKER_V_TABLE)
 407         }
 408
 409         fn create_waker() -> (Arc<AtomicBool>, Waker) {
 410                 let a = Arc::new(AtomicBool::new(false));
 411                 let waker = unsafe { Waker::from_raw(waker_clone((&a as *const Arc<AtomicBool>) as *const ())) };
 412                 (a, waker)
 413         }
 414
 415         #[test]
 416         fn test_future() {
 417                 let mut future = Future {
 418                         state: Arc::new(Mutex::new(FutureState {
 419                                 callbacks: Vec::new(),
 420                                 complete: false,
 421                                 callbacks_made: false,
 422                         }))
 423                 };
 424                 let mut second_future = Future { state: Arc::clone(&future.state) };
 425
 426                 let (woken, waker) = create_waker();
 427                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Pending);
 428                 assert!(!woken.load(Ordering::SeqCst));
 429
 430                 let (second_woken, second_waker) = create_waker();
 431                 assert_eq!(Pin::new(&mut second_future).poll(&mut Context::from_waker(&second_waker)), Poll::Pending);
 432                 assert!(!second_woken.load(Ordering::SeqCst));
 433
 434                 future.state.lock().unwrap().complete();
 435                 assert!(woken.load(Ordering::SeqCst));
 436                 assert!(second_woken.load(Ordering::SeqCst));
 437                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Ready(()));
 438                 assert_eq!(Pin::new(&mut second_future).poll(&mut Context::from_waker(&second_waker)), Poll::Ready(()));
 439         }
 440
 441         #[test]
 442         fn test_dropped_future_doesnt_count() {
 443                 // Tests that if a Future gets drop'd before it is poll()ed `Ready` it doesn't count as
 444                 // having been woken, leaving the notify-required flag set.
 445                 let notifier = Notifier::new();
 446                 notifier.notify();
 447
 448                 // If we get a future and don't touch it we're definitely still notify-required.
 449                 notifier.get_future();
 450                 assert!(notifier.wait_timeout(Duration::from_millis(1)));
 451                 assert!(!notifier.wait_timeout(Duration::from_millis(1)));
 452
 453                 // Even if we poll'd once but didn't observe a `Ready`, we should be notify-required.
 454                 let mut future = notifier.get_future();
 455                 let (woken, waker) = create_waker();
 456                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Pending);
 457
 458                 notifier.notify();
 459                 assert!(woken.load(Ordering::SeqCst));
 460                 assert!(notifier.wait_timeout(Duration::from_millis(1)));
 461
 462                 // However, once we do poll `Ready` it should wipe the notify-required flag.
 463                 let mut future = notifier.get_future();
 464                 let (woken, waker) = create_waker();
 465                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Pending);
 466
 467                 notifier.notify();
 468                 assert!(woken.load(Ordering::SeqCst));
 469                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Ready(()));
 470                 assert!(!notifier.wait_timeout(Duration::from_millis(1)));
 471         }
 472 }