_ 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 core::mem;
  17 use core::time::Duration;
  18 use sync::{Condvar, Mutex};
  19
  20 #[cfg(any(test, feature = "std"))]
  21 use std::time::Instant;
  22
  23 /// Used to signal to one of many waiters that the condition they're waiting on has happened.
  24 pub(crate) struct Notifier {
  25         /// Users won't access the lock directly, but rather wait on its bool using
  26         /// `wait_timeout` and `wait`.
  27         lock: (Mutex<bool>, Condvar),
  28 }
  29
  30 impl Notifier {
  31         pub(crate) fn new() -> Self {
  32                 Self {
  33                         lock: (Mutex::new(false), Condvar::new()),
  34                 }
  35         }
  36
  37         pub(crate) fn wait(&self) {
  38                 loop {
  39                         let &(ref mtx, ref cvar) = &self.lock;
  40                         let mut guard = mtx.lock().unwrap();
  41                         if *guard {
  42                                 *guard = false;
  43                                 return;
  44                         }
  45                         guard = cvar.wait(guard).unwrap();
  46                         let result = *guard;
  47                         if result {
  48                                 *guard = false;
  49                                 return
  50                         }
  51                 }
  52         }
  53
  54         #[cfg(any(test, feature = "std"))]
  55         pub(crate) fn wait_timeout(&self, max_wait: Duration) -> bool {
  56                 let current_time = Instant::now();
  57                 loop {
  58                         let &(ref mtx, ref cvar) = &self.lock;
  59                         let mut guard = mtx.lock().unwrap();
  60                         if *guard {
  61                                 *guard = false;
  62                                 return true;
  63                         }
  64                         guard = cvar.wait_timeout(guard, max_wait).unwrap().0;
  65                         // Due to spurious wakeups that can happen on `wait_timeout`, here we need to check if the
  66                         // desired wait time has actually passed, and if not then restart the loop with a reduced wait
  67                         // time. Note that this logic can be highly simplified through the use of
  68                         // `Condvar::wait_while` and `Condvar::wait_timeout_while`, if and when our MSRV is raised to
  69                         // 1.42.0.
  70                         let elapsed = current_time.elapsed();
  71                         let result = *guard;
  72                         if result || elapsed >= max_wait {
  73                                 *guard = false;
  74                                 return result;
  75                         }
  76                         match max_wait.checked_sub(elapsed) {
  77                                 None => return result,
  78                                 Some(_) => continue
  79                         }
  80                 }
  81         }
  82
  83         /// Wake waiters, tracking that wake needs to occur even if there are currently no waiters.
  84         pub(crate) fn notify(&self) {
  85                 let &(ref persist_mtx, ref cnd) = &self.lock;
  86                 let mut lock = persist_mtx.lock().unwrap();
  87                 *lock = true;
  88                 mem::drop(lock);
  89                 cnd.notify_all();
  90         }
  91
  92         #[cfg(any(test, feature = "_test_utils"))]
  93         pub fn notify_pending(&self) -> bool {
  94                 let &(ref mtx, _) = &self.lock;
  95                 let guard = mtx.lock().unwrap();
  96                 *guard
  97         }
  98 }
  99
 100 #[cfg(test)]
 101 mod tests {
 102         #[cfg(feature = "std")]
 103         #[test]
 104         fn test_wait_timeout() {
 105                 use super::*;
 106                 use sync::Arc;
 107                 use core::sync::atomic::{AtomicBool, Ordering};
 108                 use std::thread;
 109
 110                 let persistence_notifier = Arc::new(Notifier::new());
 111                 let thread_notifier = Arc::clone(&persistence_notifier);
 112
 113                 let exit_thread = Arc::new(AtomicBool::new(false));
 114                 let exit_thread_clone = exit_thread.clone();
 115                 thread::spawn(move || {
 116                         loop {
 117                                 let &(ref persist_mtx, ref cnd) = &thread_notifier.lock;
 118                                 let mut lock = persist_mtx.lock().unwrap();
 119                                 *lock = true;
 120                                 cnd.notify_all();
 121
 122                                 if exit_thread_clone.load(Ordering::SeqCst) {
 123                                         break
 124                                 }
 125                         }
 126                 });
 127
 128                 // Check that we can block indefinitely until updates are available.
 129                 let _ = persistence_notifier.wait();
 130
 131                 // Check that the Notifier will return after the given duration if updates are
 132                 // available.
 133                 loop {
 134                         if persistence_notifier.wait_timeout(Duration::from_millis(100)) {
 135                                 break
 136                         }
 137                 }
 138
 139                 exit_thread.store(true, Ordering::SeqCst);
 140
 141                 // Check that the Notifier will return after the given duration even if no updates
 142                 // are available.
 143                 loop {
 144                         if !persistence_notifier.wait_timeout(Duration::from_millis(100)) {
 145                                 break
 146                         }
 147                 }
 148         }
 149 }