_ 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 core::time::Duration;
  19 use sync::{Condvar, Mutex};
  20
  21 #[cfg(any(test, feature = "std"))]
  22 use std::time::Instant;
  23
  24 use core::future::Future as StdFuture;
  25 use core::task::{Context, Poll};
  26 use core::pin::Pin;
  27
  28 use prelude::*;
  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: false,
 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         pub fn register_callback(&self, callback: Box<dyn FutureCallback>) {
 167                 let mut state = self.state.lock().unwrap();
 168                 if state.complete {
 169                         mem::drop(state);
 170                         callback.call();
 171                 } else {
 172                         state.callbacks.push(callback);
 173                 }
 174         }
 175 }
 176
 177 mod std_future {
 178         use core::task::Waker;
 179         pub struct StdWaker(pub Waker);
 180         impl super::FutureCallback for StdWaker {
 181                 fn call(&self) { self.0.wake_by_ref() }
 182         }
 183 }
 184
 185 /// (C-not exported) as Rust Futures aren't usable in language bindings.
 186 impl<'a> StdFuture for Future {
 187         type Output = ();
 188
 189         fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
 190                 let mut state = self.state.lock().unwrap();
 191                 if state.complete {
 192                         Poll::Ready(())
 193                 } else {
 194                         let waker = cx.waker().clone();
 195                         state.callbacks.push(Box::new(std_future::StdWaker(waker)));
 196                         Poll::Pending
 197                 }
 198         }
 199 }
 200
 201 #[cfg(test)]
 202 mod tests {
 203         use super::*;
 204         use core::sync::atomic::{AtomicBool, Ordering};
 205         use core::future::Future as FutureTrait;
 206         use core::task::{Context, Poll, RawWaker, RawWakerVTable, Waker};
 207
 208         #[cfg(feature = "std")]
 209         #[test]
 210         fn test_wait_timeout() {
 211                 use sync::Arc;
 212                 use std::thread;
 213
 214                 let persistence_notifier = Arc::new(Notifier::new());
 215                 let thread_notifier = Arc::clone(&persistence_notifier);
 216
 217                 let exit_thread = Arc::new(AtomicBool::new(false));
 218                 let exit_thread_clone = exit_thread.clone();
 219                 thread::spawn(move || {
 220                         loop {
 221                                 let mut lock = thread_notifier.notify_pending.lock().unwrap();
 222                                 lock.0 = true;
 223                                 thread_notifier.condvar.notify_all();
 224
 225                                 if exit_thread_clone.load(Ordering::SeqCst) {
 226                                         break
 227                                 }
 228                         }
 229                 });
 230
 231                 // Check that we can block indefinitely until updates are available.
 232                 let _ = persistence_notifier.wait();
 233
 234                 // Check that the Notifier will return after the given duration if updates are
 235                 // available.
 236                 loop {
 237                         if persistence_notifier.wait_timeout(Duration::from_millis(100)) {
 238                                 break
 239                         }
 240                 }
 241
 242                 exit_thread.store(true, Ordering::SeqCst);
 243
 244                 // Check that the Notifier will return after the given duration even if no updates
 245                 // are available.
 246                 loop {
 247                         if !persistence_notifier.wait_timeout(Duration::from_millis(100)) {
 248                                 break
 249                         }
 250                 }
 251         }
 252
 253         #[test]
 254         fn test_future_callbacks() {
 255                 let future = Future {
 256                         state: Arc::new(Mutex::new(FutureState {
 257                                 callbacks: Vec::new(),
 258                                 complete: false,
 259                         }))
 260                 };
 261                 let callback = Arc::new(AtomicBool::new(false));
 262                 let callback_ref = Arc::clone(&callback);
 263                 future.register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 264
 265                 assert!(!callback.load(Ordering::SeqCst));
 266                 future.state.lock().unwrap().complete();
 267                 assert!(callback.load(Ordering::SeqCst));
 268                 future.state.lock().unwrap().complete();
 269         }
 270
 271         #[test]
 272         fn test_pre_completed_future_callbacks() {
 273                 let future = Future {
 274                         state: Arc::new(Mutex::new(FutureState {
 275                                 callbacks: Vec::new(),
 276                                 complete: false,
 277                         }))
 278                 };
 279                 future.state.lock().unwrap().complete();
 280
 281                 let callback = Arc::new(AtomicBool::new(false));
 282                 let callback_ref = Arc::clone(&callback);
 283                 future.register_callback(Box::new(move || assert!(!callback_ref.fetch_or(true, Ordering::SeqCst))));
 284
 285                 assert!(callback.load(Ordering::SeqCst));
 286                 assert!(future.state.lock().unwrap().callbacks.is_empty());
 287         }
 288
 289         // Rather annoyingly, there's no safe way in Rust std to construct a Waker despite it being
 290         // totally possible to construct from a trait implementation (though somewhat less effecient
 291         // compared to a raw VTable). Instead, we have to write out a lot of boilerplate to build a
 292         // waker, which we do here with a trivial Arc<AtomicBool> data element to track woke-ness.
 293         const WAKER_V_TABLE: RawWakerVTable = RawWakerVTable::new(waker_clone, wake, wake_by_ref, drop);
 294         unsafe fn wake_by_ref(ptr: *const ()) { let p = ptr as *const Arc<AtomicBool>; assert!(!(*p).fetch_or(true, Ordering::SeqCst)); }
 295         unsafe fn drop(ptr: *const ()) { let p = ptr as *mut Arc<AtomicBool>; Box::from_raw(p); }
 296         unsafe fn wake(ptr: *const ()) { wake_by_ref(ptr); drop(ptr); }
 297         unsafe fn waker_clone(ptr: *const ()) -> RawWaker {
 298                 let p = ptr as *const Arc<AtomicBool>;
 299                 RawWaker::new(Box::into_raw(Box::new(Arc::clone(&*p))) as *const (), &WAKER_V_TABLE)
 300         }
 301
 302         fn create_waker() -> (Arc<AtomicBool>, Waker) {
 303                 let a = Arc::new(AtomicBool::new(false));
 304                 let waker = unsafe { Waker::from_raw(waker_clone((&a as *const Arc<AtomicBool>) as *const ())) };
 305                 (a, waker)
 306         }
 307
 308         #[test]
 309         fn test_future() {
 310                 let mut future = Future {
 311                         state: Arc::new(Mutex::new(FutureState {
 312                                 callbacks: Vec::new(),
 313                                 complete: false,
 314                         }))
 315                 };
 316                 let mut second_future = Future { state: Arc::clone(&future.state) };
 317
 318                 let (woken, waker) = create_waker();
 319                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Pending);
 320                 assert!(!woken.load(Ordering::SeqCst));
 321
 322                 let (second_woken, second_waker) = create_waker();
 323                 assert_eq!(Pin::new(&mut second_future).poll(&mut Context::from_waker(&second_waker)), Poll::Pending);
 324                 assert!(!second_woken.load(Ordering::SeqCst));
 325
 326                 future.state.lock().unwrap().complete();
 327                 assert!(woken.load(Ordering::SeqCst));
 328                 assert!(second_woken.load(Ordering::SeqCst));
 329                 assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Ready(()));
 330                 assert_eq!(Pin::new(&mut second_future).poll(&mut Context::from_waker(&second_waker)), Poll::Ready(()));
 331         }
 332 }