Give `Future`s for a `FutureState` an idx and track `StdWaker` idxn

When an `std::future::Future` is `poll()`ed, we're only supposed to
use the latest `Waker` provided. However, we currently push an
`StdWaker` onto our callback list every time `poll` is called,
waking every `Waker` but also using more and more memory until the
`Future` itself is woken.

Here we take a step towards fixing this by giving each `Future` a
unique index and storing which `Future` an `StdWaker` came from in
the callback list. This sets us up to deduplicate `StdWaker`s by
`Future`s in the next commit.

diff --git a/lightning/src/util/wakers.rs b/lightning/src/util/wakers.rs
index d22932ac6249acea6cef74cc19da96fe976150bf..d220aa02dfd48bf1b5c0d64b38f31ca32f755768 100644 (file)
--- a/lightning/src/util/wakers.rs
+++ b/lightning/src/util/wakers.rs
@@ -56,16 +56,22 @@ impl Notifier {
        /// Gets a [`Future`] that will get woken up with any waiters
        pub(crate) fn get_future(&self) -> Future {
                let mut lock = self.notify_pending.lock().unwrap();
+               let mut self_idx = 0;
                if let Some(existing_state) = &lock.1 {
-                       if existing_state.lock().unwrap().callbacks_made {
+                       let mut locked = existing_state.lock().unwrap();
+                       if locked.callbacks_made {
                                // If the existing `FutureState` has completed and actually made callbacks,
                                // consider the notification flag to have been cleared and reset the future state.
+                               mem::drop(locked);
                                lock.1.take();
                                lock.0 = false;
+                       } else {
+                               self_idx = locked.next_idx;
+                               locked.next_idx += 1;
                        }
                }
                if let Some(existing_state) = &lock.1 {
-                       Future { state: Arc::clone(&existing_state) }
+                       Future { state: Arc::clone(&existing_state), self_idx }
                } else {
                        let state = Arc::new(Mutex::new(FutureState {
                                callbacks: Vec::new(),
@@ -73,9 +79,10 @@ impl Notifier {
                                callbacks_with_state: Vec::new(),
                                complete: lock.0,
                                callbacks_made: false,
+                               next_idx: 1,
                        }));
                        lock.1 = Some(Arc::clone(&state));
-                       Future { state }
+                       Future { state, self_idx: 0 }
                }
        }
 
@@ -115,10 +122,11 @@ pub(crate) struct FutureState {
        // we only count it after another `poll()` and the second wakes a `Sleeper` which handles
        // setting `callbacks_made` itself).
        callbacks: Vec<Box<dyn FutureCallback>>,
-       std_future_callbacks: Vec<StdWaker>,
+       std_future_callbacks: Vec<(usize, StdWaker)>,
        callbacks_with_state: Vec<Box<dyn Fn(&Arc<Mutex<FutureState>>) -> () + Send>>,
        complete: bool,
        callbacks_made: bool,
+       next_idx: usize,
 }
 
 fn complete_future(this: &Arc<Mutex<FutureState>>) -> bool {
@@ -128,7 +136,7 @@ fn complete_future(this: &Arc<Mutex<FutureState>>) -> bool {
                callback.call();
                state.callbacks_made = true;
        }
-       for waker in state.std_future_callbacks.drain(..) {
+       for (_, waker) in state.std_future_callbacks.drain(..) {
                waker.0.wake_by_ref();
        }
        for callback in state.callbacks_with_state.drain(..) {
@@ -139,11 +147,9 @@ fn complete_future(this: &Arc<Mutex<FutureState>>) -> bool {
 }
 
 /// A simple future which can complete once, and calls some callback(s) when it does so.
-///
-/// Clones can be made and all futures cloned from the same source will complete at the same time.
-#[derive(Clone)]
 pub struct Future {
        state: Arc<Mutex<FutureState>>,
+       self_idx: usize,
 }
 
 impl Future {
@@ -210,7 +216,7 @@ impl<'a> StdFuture for Future {
                        Poll::Ready(())
                } else {
                        let waker = cx.waker().clone();
-                       state.std_future_callbacks.push(StdWaker(waker));
+                       state.std_future_callbacks.push((self.self_idx, StdWaker(waker)));
                        Poll::Pending
                }
        }
@@ -461,7 +467,9 @@ mod tests {
                                callbacks_with_state: Vec::new(),
                                complete: false,
                                callbacks_made: false,
-                       }))
+                               next_idx: 1,
+                       })),
+                       self_idx: 0,
                };
                let callback = Arc::new(AtomicBool::new(false));
                let callback_ref = Arc::clone(&callback);
@@ -478,10 +486,13 @@ mod tests {
                let future = Future {
                        state: Arc::new(Mutex::new(FutureState {
                                callbacks: Vec::new(),
+                               std_future_callbacks: Vec::new(),
                                callbacks_with_state: Vec::new(),
                                complete: false,
                                callbacks_made: false,
-                       }))
+                               next_idx: 1,
+                       })),
+                       self_idx: 0,
                };
                complete_future(&future.state);
 
@@ -521,9 +532,11 @@ mod tests {
                                callbacks_with_state: Vec::new(),
                                complete: false,
                                callbacks_made: false,
-                       }))
+                               next_idx: 2,
+                       })),
+                       self_idx: 0,
                };
-               let mut second_future = Future { state: Arc::clone(&future.state) };
+               let mut second_future = Future { state: Arc::clone(&future.state), self_idx: 1 };
 
                let (woken, waker) = create_waker();
                assert_eq!(Pin::new(&mut future).poll(&mut Context::from_waker(&waker)), Poll::Pending);