_ 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 sync::{Condvar, Mutex};
  19
  20 use 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 impl Notifier {
  37         pub(crate) fn new() -> Self {
  38                 Self {
  39                         notify_pending: Mutex::new((false, None)),
  40                         condvar: Condvar::new(),
  41                 }
  42         }
  43
  44         pub(crate) fn wait(&self) {
  45                 loop {
  46                         let mut guard = self.notify_pending.lock().unwrap();
  47                         if guard.0 {
  48                                 guard.0 = false;
  49                                 return;
  50                         }
  51                         guard = self.condvar.wait(guard).unwrap();
  52                         let result = guard.0;
  53                         if result {
  54                                 guard.0 = false;
  55                                 return
  56                         }
  57                 }
  58         }
  59
  60         #[cfg(any(test, feature = "std"))]
  61         pub(crate) fn wait_timeout(&self, max_wait: Duration) -> bool {
  62                 let current_time = Instant::now();
  63                 loop {
  64                         let mut guard = self.notify_pending.lock().unwrap();
  65                         if guard.0 {
  66                                 guard.0 = false;
  67                                 return true;
  68                         }
  69                         guard = self.condvar.wait_timeout(guard, max_wait).unwrap().0;
  70                         // Due to spurious wakeups that can happen on `wait_timeout`, here we need to check if the
  71                         // desired wait time has actually passed, and if not then restart the loop with a reduced wait
  72                         // time. Note that this logic can be highly simplified through the use of
  73                         // `Condvar::wait_while` and `Condvar::wait_timeout_while`, if and when our MSRV is raised to
  74                         // 1.42.0.
  75                         let elapsed = current_time.elapsed();
  76                         let result = guard.0;
  77                         if result || elapsed >= max_wait {
  78                                 guard.0 = false;
  79                                 return result;
  80                         }
  81                         match max_wait.checked_sub(elapsed) {
  82                                 None => return result,
  83                                 Some(_) => continue
  84                         }
  85                 }
  86         }
  87
  88         /// Wake waiters, tracking that wake needs to occur even if there are currently no waiters.
  89         pub(crate) fn notify(&self) {
  90                 let mut lock = self.notify_pending.lock().unwrap();
  91                 lock.0 = true;
  92                 if let Some(future_state) = lock.1.take() {
  93                         future_state.lock().unwrap().complete();
  94                 }
  95                 mem::drop(lock);
  96                 self.condvar.notify_all();
  97         }
  98
  99         /// Gets a [`Future`] that will get woken up with any waiters
 100         pub(crate) fn get_future(&self) -> Future {
 101                 let mut lock = self.notify_pending.lock().unwrap();
 102                 if lock.0 {
 103                         Future {
 104                                 state: Arc::new(Mutex::new(FutureState {
 105                                         callbacks: Vec::new(),
 106                                         complete: true,
 107                                 }))
 108                         }
 109                 } else if let Some(existing_state) = &lock.1 {
 110                         Future { state: Arc::clone(&existing_state) }
 111                 } else {
 112                         let state = Arc::new(Mutex::new(FutureState {
 113                                 callbacks: Vec::new(),
 114                                 complete: false,
 115                         }));
 116                         lock.1 = Some(Arc::clone(&state));
 117                         Future { state }
 118                 }
 119         }
 120
 121         #[cfg(any(test, feature = "_test_utils"))]
 122         pub fn notify_pending(&self) -> bool {
 123                 self.notify_pending.lock().unwrap().0
 124         }
 125 }
 126
 127 /// A callback which is called when a [`Future`] completes.
 128 ///
 129 /// Note that this MUST NOT call back into LDK directly, it must instead schedule actions to be
 130 /// taken later. Rust users should use the [`std::future::Future`] implementation for [`Future`]
 131 /// instead.
 132 ///
 133 /// Note that the [`std::future::Future`] implementation may only work for runtimes which schedule
 134 /// futures when they receive a wake, rather than immediately executing them.
 135 pub trait FutureCallback : Send {
 136         /// The method which is called.
 137         fn call(&self);
 138 }
 139
 140 impl<F: Fn() + Send> FutureCallback for F {
 141         fn call(&self) { (self)(); }
 142 }
 143
 144 pub(crate) struct FutureState {
 145         callbacks: Vec<Box<dyn FutureCallback>>,
 146         complete: bool,
 147 }
 148
 149 impl FutureState {
 150         fn complete(&mut self) {
 151                 for callback in self.callbacks.drain(..) {
 152                         callback.call();
 153                 }
 154                 self.complete = true;
 155         }
 156 }
 157
 158 /// A simple future which can complete once, and calls some callback(s) when it does so.
 159 pub struct Future {
 160         state: Arc<Mutex<FutureState>>,
 161 }
 162
 163 impl Future {
 164         /// Registers a callback to be called upon completion of this future. If the future has already
 165         /// completed, the callback will be called immediately.
 166         ///
 167         /// (C-not exported) use the bindings-only `register_callback_fn` instead
 168         pub fn register_callback(&self, callback: Box<dyn FutureCallback>) {
 169                 let mut state = self.state.lock().unwrap();
 170                 if state.complete {
 171                         mem::drop(state);
 172                         callback.call();
 173                 } else {
 174                         state.callbacks.push(callback);
 175                 }
 176         }
 177
 178         // C bindings don't (currently) know how to map `Box<dyn Trait>`, and while it could add the
 179         // following wrapper, doing it in the bindings is currently much more work than simply doing it
 180         // here.
 181         /// Registers a callback to be called upon completion of this future. If the future has already
 182         /// completed, the callback will be called immediately.
 183         #[cfg(c_bindings)]
 184         pub fn register_callback_fn<F: 'static + FutureCallback>(&self, callback: F) {
 185                 self.register_callback(Box::new(callback));
 186         }
 187 }
 188
 189 mod std_future {
 190         use core::task::Waker;
 191         pub struct StdWaker(pub Waker);
 192         impl super::FutureCallback for StdWaker {
 193                 fn call(&self) { self.0.wake_by_ref() }
 194         }
 195 }
 196
 197 /// (C-not exported) as Rust Futures aren't usable in language bindings.
 198 impl<'a> StdFuture for Future {
 199         type Output = ();
 200
 201         fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
 202                 let mut state = self.state.lock().unwrap();
 203                 if state.complete {
 204                         Poll::Ready(())
 205                 } else {
 206                         let waker = cx.waker().clone();
 207                         state.callbacks.push(Box::new(std_future::StdWaker(waker)));
 208                         Poll::Pending
 209                 }
 210         }
 211 }
 212
 213 #[cfg(test)]
 214 mod tests {
 215         use super::*;
 216         use core::sync::atomic::{AtomicBool, Ordering};
 217         use core::future::Future as FutureTrait;
 218         use core::task::{Context, Poll, RawWaker, RawWakerVTable, Waker};
 219
 220         #[test]
 221         fn notifier_pre_notified_future() {
 222                 // Previously, if we generated a future after a `Notifier` had been notified, the future
 223                 // would never complete. This tests this behavior, ensuring the future instead completes
 224                 // immediately.
 225                 let notifier = Notifier::new();
 226                 notifier.notify();
 227
 228                 let callback = Arc::new(AtomicBool::new(false));
 229                 let callback_ref = Arc::clone(&callback);
 230                 notifier.get_future().register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 231                 assert!(callback.load(Ordering::SeqCst));
 232         }
 233
 234         #[cfg(feature = "std")]
 235         #[test]
 236         fn test_wait_timeout() {
 237                 use sync::Arc;
 238                 use std::thread;
 239
 240                 let persistence_notifier = Arc::new(Notifier::new());
 241                 let thread_notifier = Arc::clone(&persistence_notifier);
 242
 243                 let exit_thread = Arc::new(AtomicBool::new(false));
 244                 let exit_thread_clone = exit_thread.clone();
 245                 thread::spawn(move || {
 246                         loop {
 247                                 let mut lock = thread_notifier.notify_pending.lock().unwrap();
 248                                 lock.0 = true;
 249                                 thread_notifier.condvar.notify_all();
 250
 251                                 if exit_thread_clone.load(Ordering::SeqCst) {
 252                                         break
 253                                 }
 254                         }
 255                 });
 256
 257                 // Check that we can block indefinitely until updates are available.
 258                 let _ = persistence_notifier.wait();
 259
 260                 // Check that the Notifier will return after the given duration if updates are
 261                 // available.
 262                 loop {
 263                         if persistence_notifier.wait_timeout(Duration::from_millis(100)) {
 264                                 break
 265                         }
 266                 }
 267
 268                 exit_thread.store(true, Ordering::SeqCst);
 269
 270                 // Check that the Notifier will return after the given duration even if no updates
 271                 // are available.
 272                 loop {
 273                         if !persistence_notifier.wait_timeout(Duration::from_millis(100)) {
 274                                 break
 275                         }
 276                 }
 277         }
 278
 279         #[test]
 280         fn test_future_callbacks() {
 281                 let future = Future {
 282                         state: Arc::new(Mutex::new(FutureState {
 283                                 callbacks: Vec::new(),
 284                                 complete: false,
 285                         }))
 286                 };
 287                 let callback = Arc::new(AtomicBool::new(false));
 288                 let callback_ref = Arc::clone(&callback);
 289                 future.register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 290
 291                 assert!(!callback.load(Ordering::SeqCst));
 292                 future.state.lock().unwrap().complete();
 293                 assert!(callback.load(Ordering::SeqCst));
 294                 future.state.lock().unwrap().complete();
 295         }
 296
 297         #[test]
 298         fn test_pre_completed_future_callbacks() {
 299                 let future = Future {
 300                         state: Arc::new(Mutex::new(FutureState {
 301                                 callbacks: Vec::new(),
 302                                 complete: false,
 303                         }))
 304                 };
 305                 future.state.lock().unwrap().complete();
 306
 307                 let callback = Arc::new(AtomicBool::new(false));
 308                 let callback_ref = Arc::clone(&callback);
 309                 future.register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 310
 311                 assert!(callback.load(Ordering::SeqCst));
 312                 assert!(future.state.lock().unwrap().callbacks.is_empty());
 313         }
 314
 315         // Rather annoyingly, there's no safe way in Rust std to construct a Waker despite it being
 316         // totally possible to construct from a trait implementation (though somewhat less effecient
 317         // compared to a raw VTable). Instead, we have to write out a lot of boilerplate to build a
 318         // waker, which we do here with a trivial Arc<AtomicBool> data element to track woke-ness.
 319         const WAKER_V_TABLE: RawWakerVTable = RawWakerVTable::new(waker_clone, wake, wake_by_ref, drop);
 320         unsafe fn wake_by_ref(ptr: *const ()) { let p = ptr as *const Arc<AtomicBool>; assert!(!(*p).fetch_or(true, Ordering::SeqCst)); }
 321         unsafe fn drop(ptr: *const ()) { let p = ptr as *mut Arc<AtomicBool>; let _freed = Box::from_raw(p); }
 322         unsafe fn wake(ptr: *const ()) { wake_by_ref(ptr); drop(ptr); }
 323         unsafe fn waker_clone(ptr: *const ()) -> RawWaker {
 324                 let p = ptr as *const Arc<AtomicBool>;
 325                 RawWaker::new(Box::into_raw(Box::new(Arc::clone(&*p))) as *const (), &WAKER_V_TABLE)
 326         }
 327
 328         fn create_waker() -> (Arc<AtomicBool>, Waker) {
 329                 let a = Arc::new(AtomicBool::new(false));
 330                 let waker = unsafe { Waker::from_raw(waker_clone((&a as *const Arc<AtomicBool>) as *const ())) };
 331                 (a, waker)
 332         }
 333
 334         #[test]
 335         fn test_future() {
 336                 let mut future = Future {
 337                         state: Arc::new(Mutex::new(FutureState {
 338                                 callbacks: Vec::new(),
 339                                 complete: false,
 340                         }))
 341                 };
 342                 let mut second_future = Future { state: Arc::clone(&future.state) };
 343
 344                 let (woken, waker) = create_waker();
 345                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Pending);
 346                 assert!(!woken.load(Ordering::SeqCst));
 347
 348                 let (second_woken, second_waker) = create_waker();
 349                 assert_eq!(Pin::new(&mut second_future).poll(&mut Context::from_waker(&second_waker)), Poll::Pending);
 350                 assert!(!second_woken.load(Ordering::SeqCst));
 351
 352                 future.state.lock().unwrap().complete();
 353                 assert!(woken.load(Ordering::SeqCst));
 354                 assert!(second_woken.load(Ordering::SeqCst));
 355                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Ready(()));
 356                 assert_eq!(Pin::new(&mut second_future).poll(&mut Context::from_waker(&second_waker)), Poll::Ready(()));
 357         }
 358 }