perf(providers): replace wake_by_ref with loop (#1428)

ethers-providers/src/stream.rs

@@ -1,9 +1,7 @@
 #![allow(clippy::return_self_not_must_use)]
 
 use crate::{JsonRpcClient, Middleware, PinBoxFut, Provider, ProviderError};
-
 use ethers_core::types::{Transaction, TxHash, U256};
-
 use futures_core::{stream::Stream, Future};
 use futures_util::{stream, stream::FuturesUnordered, FutureExt, StreamExt};
 use pin_project::pin_project;
@@ -37,8 +35,8 @@ enum FilterWatcherState<'a, R> {
 }
 
 #[must_use = "filters do nothing unless you stream them"]
-#[pin_project]
 /// Streams data from an installed filter via `eth_getFilterChanges`
+#[pin_project]
 pub struct FilterWatcher<'a, P, R> {
     /// The filter's installed id on the ethereum node
     pub id: U256,
@@ -47,7 +45,7 @@ pub struct FilterWatcher<'a, P, R> {
 
     // The polling interval
     interval: Box<dyn Stream<Item = ()> + Send + Unpin>,
-
+    /// statemachine driven by the Stream impl
     state: FilterWatcherState<'a, R>,
 }
 
@@ -79,8 +77,7 @@ where
     }
 }
 
-// Pattern for flattening the returned Vec of filter changes taken from
-// https://github.com/tomusdrw/rust-web3/blob/f043b222744580bf4be043da757ab0b300c3b2da/src/api/eth_filter.rs#L50-L67
+// Advances the filter's state machine
 impl<'a, P, R> Stream for FilterWatcher<'a, P, R>
 where
     P: JsonRpcClient,
@@ -89,16 +86,14 @@ where
     type Item = R;
 
     fn poll_next(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
-        let this = self.project();
+        let mut this = self.project();
         let id = *this.id;
 
-        *this.state = match this.state {
+        loop {
+            *this.state = match &mut this.state {
                 FilterWatcherState::WaitForInterval => {
                     // Wait the polling period
                     let _ready = futures_util::ready!(this.interval.poll_next_unpin(cx));
-
-                // create a new instance of the future
-                cx.waker().wake_by_ref();
                     let fut = Box::pin(this.provider.get_filter_changes(id));
                     FilterWatcherState::GetFilterChanges(fut)
                 }
@@ -107,8 +102,8 @@ where
                     // vector. Should we make this return a Result instead? Ideally if we're
                     // in a streamed loop we wouldn't want the loop to terminate if an error
                     // is encountered (since it might be a temporary error).
-                let items: Vec<R> = futures_util::ready!(fut.as_mut().poll(cx)).unwrap_or_default();
-                cx.waker().wake_by_ref();
+                    let items: Vec<R> =
+                        futures_util::ready!(fut.as_mut().poll(cx)).unwrap_or_default();
                     FilterWatcherState::NextItem(items.into_iter())
                 }
                 // Consume 1 element from the vector. If more elements are in the vector,
@@ -116,15 +111,13 @@ where
                 // filter changes again. Once the whole vector is consumed, it will poll again
                 // for new logs
                 FilterWatcherState::NextItem(iter) => {
-                cx.waker().wake_by_ref();
-                match iter.next() {
-                    Some(item) => return Poll::Ready(Some(item)),
-                    None => FilterWatcherState::WaitForInterval,
+                    if let item @ Some(_) = iter.next() {
+                        return Poll::Ready(item)
                     }
+                    FilterWatcherState::WaitForInterval
                 }
             };
-
-        Poll::Pending
+        }
     }
 }