_ 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                         if future_state.lock().unwrap().complete() {
 109                                 lock.1 = None;
 110                                 return;
 111                         }
 112                 }
 113                 lock.0 = true;
 114                 mem::drop(lock);
 115                 self.condvar.notify_all();
 116         }
 117
 118         /// Gets a [`Future`] that will get woken up with any waiters
 119         pub(crate) fn get_future(&self) -> Future {
 120                 let mut lock = self.propagate_future_state_to_notify_flag();
 121                 if let Some(existing_state) = &lock.1 {
 122                         Future { state: Arc::clone(&existing_state) }
 123                 } else {
 124                         let state = Arc::new(Mutex::new(FutureState {
 125                                 callbacks: Vec::new(),
 126                                 complete: lock.0,
 127                                 callbacks_made: false,
 128                         }));
 129                         lock.1 = Some(Arc::clone(&state));
 130                         Future { state }
 131                 }
 132         }
 133
 134         #[cfg(any(test, feature = "_test_utils"))]
 135         pub fn notify_pending(&self) -> bool {
 136                 self.notify_pending.lock().unwrap().0
 137         }
 138 }
 139
 140 /// A callback which is called when a [`Future`] completes.
 141 ///
 142 /// Note that this MUST NOT call back into LDK directly, it must instead schedule actions to be
 143 /// taken later. Rust users should use the [`std::future::Future`] implementation for [`Future`]
 144 /// instead.
 145 ///
 146 /// Note that the [`std::future::Future`] implementation may only work for runtimes which schedule
 147 /// futures when they receive a wake, rather than immediately executing them.
 148 pub trait FutureCallback : Send {
 149         /// The method which is called.
 150         fn call(&self);
 151 }
 152
 153 impl<F: Fn() + Send> FutureCallback for F {
 154         fn call(&self) { (self)(); }
 155 }
 156
 157 pub(crate) struct FutureState {
 158         // When we're tracking whether a callback counts as having woken the user's code, we check the
 159         // first bool - set to false if we're just calling a Waker, and true if we're calling an actual
 160         // user-provided function.
 161         callbacks: Vec<(bool, Box<dyn FutureCallback>)>,
 162         complete: bool,
 163         callbacks_made: bool,
 164 }
 165
 166 impl FutureState {
 167         fn complete(&mut self) -> bool {
 168                 for (counts_as_call, callback) in self.callbacks.drain(..) {
 169                         callback.call();
 170                         self.callbacks_made |= counts_as_call;
 171                 }
 172                 self.complete = true;
 173                 self.callbacks_made
 174         }
 175 }
 176
 177 /// A simple future which can complete once, and calls some callback(s) when it does so.
 178 pub struct Future {
 179         state: Arc<Mutex<FutureState>>,
 180 }
 181
 182 impl Future {
 183         /// Registers a callback to be called upon completion of this future. If the future has already
 184         /// completed, the callback will be called immediately.
 185         ///
 186         /// (C-not exported) use the bindings-only `register_callback_fn` instead
 187         pub fn register_callback(&self, callback: Box<dyn FutureCallback>) {
 188                 let mut state = self.state.lock().unwrap();
 189                 if state.complete {
 190                         state.callbacks_made = true;
 191                         mem::drop(state);
 192                         callback.call();
 193                 } else {
 194                         state.callbacks.push((true, callback));
 195                 }
 196         }
 197
 198         // C bindings don't (currently) know how to map `Box<dyn Trait>`, and while it could add the
 199         // following wrapper, doing it in the bindings is currently much more work than simply doing it
 200         // here.
 201         /// Registers a callback to be called upon completion of this future. If the future has already
 202         /// completed, the callback will be called immediately.
 203         #[cfg(c_bindings)]
 204         pub fn register_callback_fn<F: 'static + FutureCallback>(&self, callback: F) {
 205                 self.register_callback(Box::new(callback));
 206         }
 207 }
 208
 209 use core::task::Waker;
 210 struct StdWaker(pub Waker);
 211 impl FutureCallback for StdWaker {
 212         fn call(&self) { self.0.wake_by_ref() }
 213 }
 214
 215 /// (C-not exported) as Rust Futures aren't usable in language bindings.
 216 impl<'a> StdFuture for Future {
 217         type Output = ();
 218
 219         fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
 220                 let mut state = self.state.lock().unwrap();
 221                 if state.complete {
 222                         state.callbacks_made = true;
 223                         Poll::Ready(())
 224                 } else {
 225                         let waker = cx.waker().clone();
 226                         state.callbacks.push((false, Box::new(StdWaker(waker))));
 227                         Poll::Pending
 228                 }
 229         }
 230 }
 231
 232 #[cfg(test)]
 233 mod tests {
 234         use super::*;
 235         use core::sync::atomic::{AtomicBool, Ordering};
 236         use core::future::Future as FutureTrait;
 237         use core::task::{Context, Poll, RawWaker, RawWakerVTable, Waker};
 238
 239         #[test]
 240         fn notifier_pre_notified_future() {
 241                 // Previously, if we generated a future after a `Notifier` had been notified, the future
 242                 // would never complete. This tests this behavior, ensuring the future instead completes
 243                 // immediately.
 244                 let notifier = Notifier::new();
 245                 notifier.notify();
 246
 247                 let callback = Arc::new(AtomicBool::new(false));
 248                 let callback_ref = Arc::clone(&callback);
 249                 notifier.get_future().register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 250                 assert!(callback.load(Ordering::SeqCst));
 251         }
 252
 253         #[test]
 254         fn notifier_future_completes_wake() {
 255                 // Previously, if we were only using the `Future` interface to learn when a `Notifier` has
 256                 // been notified, we'd never mark the notifier as not-awaiting-notify. This caused the
 257                 // `lightning-background-processor` to persist in a tight loop.
 258                 let notifier = Notifier::new();
 259
 260                 // First check the simple case, ensuring if we get notified a new future isn't woken until
 261                 // a second `notify`.
 262                 let callback = Arc::new(AtomicBool::new(false));
 263                 let callback_ref = Arc::clone(&callback);
 264                 notifier.get_future().register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 265                 assert!(!callback.load(Ordering::SeqCst));
 266
 267                 notifier.notify();
 268                 assert!(callback.load(Ordering::SeqCst));
 269
 270                 let callback = Arc::new(AtomicBool::new(false));
 271                 let callback_ref = Arc::clone(&callback);
 272                 notifier.get_future().register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 273                 assert!(!callback.load(Ordering::SeqCst));
 274
 275                 notifier.notify();
 276                 assert!(callback.load(Ordering::SeqCst));
 277
 278                 // Then check the case where the future is fetched before the notification, but a callback
 279                 // is only registered after the `notify`, ensuring that it is still sufficient to ensure we
 280                 // don't get an instant-wake when we get a new future.
 281                 let future = notifier.get_future();
 282                 notifier.notify();
 283
 284                 let callback = Arc::new(AtomicBool::new(false));
 285                 let callback_ref = Arc::clone(&callback);
 286                 future.register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 287                 assert!(callback.load(Ordering::SeqCst));
 288
 289                 let callback = Arc::new(AtomicBool::new(false));
 290                 let callback_ref = Arc::clone(&callback);
 291                 notifier.get_future().register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 292                 assert!(!callback.load(Ordering::SeqCst));
 293         }
 294
 295         #[test]
 296         fn new_future_wipes_notify_bit() {
 297                 // Previously, if we were only using the `Future` interface to learn when a `Notifier` has
 298                 // been notified, we'd never mark the notifier as not-awaiting-notify if a `Future` is
 299                 // fetched after the notify bit has been set.
 300                 let notifier = Notifier::new();
 301                 notifier.notify();
 302
 303                 let callback = Arc::new(AtomicBool::new(false));
 304                 let callback_ref = Arc::clone(&callback);
 305                 notifier.get_future().register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 306                 assert!(callback.load(Ordering::SeqCst));
 307
 308                 let callback = Arc::new(AtomicBool::new(false));
 309                 let callback_ref = Arc::clone(&callback);
 310                 notifier.get_future().register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 311                 assert!(!callback.load(Ordering::SeqCst));
 312
 313                 notifier.notify();
 314                 assert!(callback.load(Ordering::SeqCst));
 315         }
 316
 317         #[cfg(feature = "std")]
 318         #[test]
 319         fn test_wait_timeout() {
 320                 use crate::sync::Arc;
 321                 use std::thread;
 322
 323                 let persistence_notifier = Arc::new(Notifier::new());
 324                 let thread_notifier = Arc::clone(&persistence_notifier);
 325
 326                 let exit_thread = Arc::new(AtomicBool::new(false));
 327                 let exit_thread_clone = exit_thread.clone();
 328                 thread::spawn(move || {
 329                         loop {
 330                                 let mut lock = thread_notifier.notify_pending.lock().unwrap();
 331                                 lock.0 = true;
 332                                 thread_notifier.condvar.notify_all();
 333
 334                                 if exit_thread_clone.load(Ordering::SeqCst) {
 335                                         break
 336                                 }
 337                         }
 338                 });
 339
 340                 // Check that we can block indefinitely until updates are available.
 341                 let _ = persistence_notifier.wait();
 342
 343                 // Check that the Notifier will return after the given duration if updates are
 344                 // available.
 345                 loop {
 346                         if persistence_notifier.wait_timeout(Duration::from_millis(100)) {
 347                                 break
 348                         }
 349                 }
 350
 351                 exit_thread.store(true, Ordering::SeqCst);
 352
 353                 // Check that the Notifier will return after the given duration even if no updates
 354                 // are available.
 355                 loop {
 356                         if !persistence_notifier.wait_timeout(Duration::from_millis(100)) {
 357                                 break
 358                         }
 359                 }
 360         }
 361
 362         #[test]
 363         fn test_future_callbacks() {
 364                 let future = Future {
 365                         state: Arc::new(Mutex::new(FutureState {
 366                                 callbacks: Vec::new(),
 367                                 complete: false,
 368                                 callbacks_made: false,
 369                         }))
 370                 };
 371                 let callback = Arc::new(AtomicBool::new(false));
 372                 let callback_ref = Arc::clone(&callback);
 373                 future.register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 374
 375                 assert!(!callback.load(Ordering::SeqCst));
 376                 future.state.lock().unwrap().complete();
 377                 assert!(callback.load(Ordering::SeqCst));
 378                 future.state.lock().unwrap().complete();
 379         }
 380
 381         #[test]
 382         fn test_pre_completed_future_callbacks() {
 383                 let future = Future {
 384                         state: Arc::new(Mutex::new(FutureState {
 385                                 callbacks: Vec::new(),
 386                                 complete: false,
 387                                 callbacks_made: false,
 388                         }))
 389                 };
 390                 future.state.lock().unwrap().complete();
 391
 392                 let callback = Arc::new(AtomicBool::new(false));
 393                 let callback_ref = Arc::clone(&callback);
 394                 future.register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 395
 396                 assert!(callback.load(Ordering::SeqCst));
 397                 assert!(future.state.lock().unwrap().callbacks.is_empty());
 398         }
 399
 400         // Rather annoyingly, there's no safe way in Rust std to construct a Waker despite it being
 401         // totally possible to construct from a trait implementation (though somewhat less effecient
 402         // compared to a raw VTable). Instead, we have to write out a lot of boilerplate to build a
 403         // waker, which we do here with a trivial Arc<AtomicBool> data element to track woke-ness.
 404         const WAKER_V_TABLE: RawWakerVTable = RawWakerVTable::new(waker_clone, wake, wake_by_ref, drop);
 405         unsafe fn wake_by_ref(ptr: *const ()) { let p = ptr as *const Arc<AtomicBool>; assert!(!(*p).fetch_or(true, Ordering::SeqCst)); }
 406         unsafe fn drop(ptr: *const ()) { let p = ptr as *mut Arc<AtomicBool>; let _freed = Box::from_raw(p); }
 407         unsafe fn wake(ptr: *const ()) { wake_by_ref(ptr); drop(ptr); }
 408         unsafe fn waker_clone(ptr: *const ()) -> RawWaker {
 409                 let p = ptr as *const Arc<AtomicBool>;
 410                 RawWaker::new(Box::into_raw(Box::new(Arc::clone(&*p))) as *const (), &WAKER_V_TABLE)
 411         }
 412
 413         fn create_waker() -> (Arc<AtomicBool>, Waker) {
 414                 let a = Arc::new(AtomicBool::new(false));
 415                 let waker = unsafe { Waker::from_raw(waker_clone((&a as *const Arc<AtomicBool>) as *const ())) };
 416                 (a, waker)
 417         }
 418
 419         #[test]
 420         fn test_future() {
 421                 let mut future = Future {
 422                         state: Arc::new(Mutex::new(FutureState {
 423                                 callbacks: Vec::new(),
 424                                 complete: false,
 425                                 callbacks_made: false,
 426                         }))
 427                 };
 428                 let mut second_future = Future { state: Arc::clone(&future.state) };
 429
 430                 let (woken, waker) = create_waker();
 431                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Pending);
 432                 assert!(!woken.load(Ordering::SeqCst));
 433
 434                 let (second_woken, second_waker) = create_waker();
 435                 assert_eq!(Pin::new(&mut second_future).poll(&mut Context::from_waker(&second_waker)), Poll::Pending);
 436                 assert!(!second_woken.load(Ordering::SeqCst));
 437
 438                 future.state.lock().unwrap().complete();
 439                 assert!(woken.load(Ordering::SeqCst));
 440                 assert!(second_woken.load(Ordering::SeqCst));
 441                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Ready(()));
 442                 assert_eq!(Pin::new(&mut second_future).poll(&mut Context::from_waker(&second_waker)), Poll::Ready(()));
 443         }
 444
 445         #[test]
 446         fn test_dropped_future_doesnt_count() {
 447                 // Tests that if a Future gets drop'd before it is poll()ed `Ready` it doesn't count as
 448                 // having been woken, leaving the notify-required flag set.
 449                 let notifier = Notifier::new();
 450                 notifier.notify();
 451
 452                 // If we get a future and don't touch it we're definitely still notify-required.
 453                 notifier.get_future();
 454                 assert!(notifier.wait_timeout(Duration::from_millis(1)));
 455                 assert!(!notifier.wait_timeout(Duration::from_millis(1)));
 456
 457                 // Even if we poll'd once but didn't observe a `Ready`, we should be notify-required.
 458                 let mut future = notifier.get_future();
 459                 let (woken, waker) = create_waker();
 460                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Pending);
 461
 462                 notifier.notify();
 463                 assert!(woken.load(Ordering::SeqCst));
 464                 assert!(notifier.wait_timeout(Duration::from_millis(1)));
 465
 466                 // However, once we do poll `Ready` it should wipe the notify-required flag.
 467                 let mut future = notifier.get_future();
 468                 let (woken, waker) = create_waker();
 469                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Pending);
 470
 471                 notifier.notify();
 472                 assert!(woken.load(Ordering::SeqCst));
 473                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Ready(()));
 474                 assert!(!notifier.wait_timeout(Duration::from_millis(1)));
 475         }
 476
 477         #[test]
 478         fn test_poll_post_notify_completes() {
 479                 // Tests that if we have a future state that has completed, and we haven't yet requested a
 480                 // new future, if we get a notify prior to requesting that second future it is generated
 481                 // pre-completed.
 482                 let notifier = Notifier::new();
 483
 484                 notifier.notify();
 485                 let mut future = notifier.get_future();
 486                 let (woken, waker) = create_waker();
 487                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Ready(()));
 488                 assert!(!woken.load(Ordering::SeqCst));
 489
 490                 notifier.notify();
 491                 let mut future = notifier.get_future();
 492                 let (woken, waker) = create_waker();
 493                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Ready(()));
 494                 assert!(!woken.load(Ordering::SeqCst));
 495
 496                 let mut future = notifier.get_future();
 497                 let (woken, waker) = create_waker();
 498                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Pending);
 499                 assert!(!woken.load(Ordering::SeqCst));
 500
 501                 notifier.notify();
 502                 assert!(woken.load(Ordering::SeqCst));
 503                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Ready(()));
 504         }
 505
 506         #[test]
 507         fn test_poll_post_notify_completes_initial_notified() {
 508                 // Identical to the previous test, but the first future completes via a wake rather than an
 509                 // immediate `Poll::Ready`.
 510                 let notifier = Notifier::new();
 511
 512                 let mut future = notifier.get_future();
 513                 let (woken, waker) = create_waker();
 514                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Pending);
 515
 516                 notifier.notify();
 517                 assert!(woken.load(Ordering::SeqCst));
 518                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Ready(()));
 519
 520                 notifier.notify();
 521                 let mut future = notifier.get_future();
 522                 let (woken, waker) = create_waker();
 523                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Ready(()));
 524                 assert!(!woken.load(Ordering::SeqCst));
 525
 526                 let mut future = notifier.get_future();
 527                 let (woken, waker) = create_waker();
 528                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Pending);
 529                 assert!(!woken.load(Ordering::SeqCst));
 530
 531                 notifier.notify();
 532                 assert!(woken.load(Ordering::SeqCst));
 533                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Ready(()));
 534         }
 535 }