Split lists of Waker and directly-registered Future callbacks

In the next commit we'll fix a memory leak due to keeping too many
`std::task::Waker` callbacks in `FutureState` from redundant `poll`
calls, but first we need to split handling of `StdWaker`-based
future wake callbacks from normal ones, which we do here.

Author: TheBlueMatt

lightning/src/util/wakers.rs

@@ -69,6 +69,7 @@ impl Notifier {
 		} else {
 			let state = Arc::new(Mutex::new(FutureState {
 				callbacks: Vec::new(),
+				std_future_callbacks: Vec::new(),
 				callbacks_with_state: Vec::new(),
 				complete: lock.0,
 				callbacks_made: false,
@@ -112,7 +113,8 @@ pub(crate) struct FutureState {
 	// When we're tracking whether a callback counts as having woken the user's code, we check the
 	// first bool - set to false if we're just calling a Waker, and true if we're calling an actual
 	// user-provided function.
-	callbacks: Vec<(bool, Box<dyn FutureCallback>)>,
+	callbacks: Vec<Box<dyn FutureCallback>>,
+	std_future_callbacks: Vec<StdWaker>,
 	callbacks_with_state: Vec<(bool, Box<dyn Fn(&Arc<Mutex<FutureState>>) -> () + Send>)>,
 	complete: bool,
 	callbacks_made: bool,
@@ -121,9 +123,12 @@ pub(crate) struct FutureState {
 fn complete_future(this: &Arc<Mutex<FutureState>>) -> bool {
 	let mut state_lock = this.lock().unwrap();
 	let state = &mut *state_lock;
-	for (counts_as_call, callback) in state.callbacks.drain(..) {
+	for callback in state.callbacks.drain(..) {
 		callback.call();
-		state.callbacks_made |= counts_as_call;
+		state.callbacks_made = true;
+	}
+	for waker in state.std_future_callbacks.drain(..) {
+		waker.0.wake_by_ref();
 	}
 	for (counts_as_call, callback) in state.callbacks_with_state.drain(..) {
 		(callback)(this);
@@ -153,7 +158,7 @@ impl Future {
 			mem::drop(state);
 			callback.call();
 		} else {
-			state.callbacks.push((true, callback));
+			state.callbacks.push(callback);
 		}
 	}
 
@@ -193,9 +198,6 @@ impl Future {
 
 use core::task::Waker;
 struct StdWaker(pub Waker);
-impl FutureCallback for StdWaker {
-	fn call(&self) { self.0.wake_by_ref() }
-}
 
 /// This is not exported to bindings users as Rust Futures aren't usable in language bindings.
 impl<'a> StdFuture for Future {
@@ -208,7 +210,7 @@ impl<'a> StdFuture for Future {
 			Poll::Ready(())
 		} else {
 			let waker = cx.waker().clone();
-			state.callbacks.push((false, Box::new(StdWaker(waker))));
+			state.std_future_callbacks.push(StdWaker(waker));
 			Poll::Pending
 		}
 	}
@@ -455,6 +457,7 @@ 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,
@@ -514,6 +517,7 @@ mod tests {
 		let mut 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,