1 files changed, 67 insertions, 0 deletions
diff --git a/helix-event/src/debounce.rs b/helix-event/src/debounce.rs
new file mode 100644
index 00000000..30b6f671
--- /dev/null
+++ b/helix-event/src/debounce.rs
@@ -0,0 +1,67 @@
+//! Utilities for declaring an async (usually debounced) hook
+
+use std::time::Duration;
+
+use futures_executor::block_on;
+use tokio::sync::mpsc::{self, error::TrySendError, Sender};
+use tokio::time::Instant;
+
+/// Async hooks provide a convenient framework for implementing (debounced)
+/// async event handlers. Most synchronous event hooks will likely need to
+/// debounce their events, coordinate multiple different hooks and potentially
+/// track some state. `AsyncHooks` facilitate these use cases by running as
+/// a background tokio task that waits for events (usually an enum) to be
+/// sent through a channel.
+pub trait AsyncHook: Sync + Send + 'static + Sized {
+    type Event: Sync + Send + 'static;
+    /// Called immediately whenever an event is received, this function can
+    /// consume the event immediately or debounce it. In case of debouncing,
+    /// it can either define a new debounce timeout or continue the current one
+    fn handle_event(&mut self, event: Self::Event, timeout: Option<Instant>) -> Option<Instant>;
+
+    /// Called whenever the debounce timeline is reached
+    fn finish_debounce(&mut self);
+
+    fn spawn(self) -> mpsc::Sender<Self::Event> {
+        // the capacity doesn't matter too much here, unless the cpu is totally overwhelmed
+        // the cap will never be reached since we always immediately drain the channel
+        // so it should only be reached in case of total CPU overload.
+        // However, a bounded channel is much more efficient so it's nice to use here
+        let (tx, rx) = mpsc::channel(128);
+        tokio::spawn(run(self, rx));
+        tx
+    }
+}
+
+async fn run<Hook: AsyncHook>(mut hook: Hook, mut rx: mpsc::Receiver<Hook::Event>) {
+    let mut deadline = None;
+    loop {
+        let event = match deadline {
+            Some(deadline_) => {
+                let res = tokio::time::timeout_at(deadline_, rx.recv()).await;
+                match res {
+                    Ok(event) => event,
+                    Err(_) => {
+                        hook.finish_debounce();
+                        deadline = None;
+                        continue;
+                    }
+                }
+            }
+            None => rx.recv().await,
+        };
+        let Some(event) = event else {
+            break;
+        };
+        deadline = hook.handle_event(event, deadline);
+    }
+}
+
+pub fn send_blocking<T>(tx: &Sender<T>, data: T) {
+    // block_on has some overhead and in practice the channel should basically
+    // never be full anyway so first try sending without blocking
+    if let Err(TrySendError::Full(data)) = tx.try_send(data) {
+        // set a timeout so that we just drop a message instead of freezing the editor in the worst case
+        let _ = block_on(tx.send_timeout(data, Duration::from_millis(10)));
+    }
+}