perf: detach the watch registration from the main thread (#2224)

Author: sxyazi

Diff for: yazi-core/src/manager/watcher.rs

@@ -96,28 +96,17 @@ impl Watcher {
 		});
 	}
 
-	async fn fan_in(mut rx: watch::Receiver<HashSet<Url>>, mut watcher: impl notify::Watcher) {
+	async fn fan_in(
+		mut rx: watch::Receiver<HashSet<Url>>,
+		mut watcher: impl notify::Watcher + Send + 'static,
+	) {
 		loop {
-			let (mut to_unwatch, mut to_watch): (HashSet<_>, HashSet<_>) = {
+			let (to_unwatch, to_watch): (HashSet<_>, HashSet<_>) = {
 				let (new, old) = (&*rx.borrow_and_update(), &*WATCHED.read());
 				(old.difference(new).cloned().collect(), new.difference(old).cloned().collect())
 			};
 
-			to_unwatch.retain(|u| match watcher.unwatch(u) {
-				Ok(_) => true,
-				Err(e) if matches!(e.kind, notify::ErrorKind::WatchNotFound) => true,
-				Err(e) => {
-					error!("Unwatch failed: {e:?}");
-					false
-				}
-			});
-			to_watch.retain(|u| watcher.watch(u, RecursiveMode::NonRecursive).is_ok());
-
-			{
-				let mut watched = WATCHED.write();
-				watched.retain(|u| !to_unwatch.contains(u));
-				watched.extend(to_watch);
-			}
+			watcher = Self::sync_watched(watcher, to_unwatch, to_watch).await;
 
 			if !rx.has_changed().unwrap_or(false) {
 				Self::sync_linked().await;
@@ -173,6 +162,35 @@ impl Watcher {
 		}
 	}
 
+	async fn sync_watched<W>(mut watcher: W, to_unwatch: HashSet<Url>, to_watch: HashSet<Url>) -> W
+	where
+		W: notify::Watcher + Send + 'static,
+	{
+		use notify::ErrorKind::WatchNotFound;
+
+		if to_unwatch.is_empty() && to_watch.is_empty() {
+			return watcher;
+		}
+
+		tokio::task::spawn_blocking(move || {
+			for u in to_unwatch {
+				match watcher.unwatch(&u) {
+					Ok(()) => _ = WATCHED.write().remove(&u),
+					Err(e) if matches!(e.kind, WatchNotFound) => _ = WATCHED.write().remove(&u),
+					Err(e) => error!("Unwatch failed: {e:?}"),
+				}
+			}
+			for u in to_watch {
+				if watcher.watch(&u, RecursiveMode::NonRecursive).is_ok() {
+					WATCHED.write().insert(u);
+				}
+			}
+			watcher
+		})
+		.await
+		.unwrap()
+	}
+
 	async fn sync_linked() {
 		let mut new = WATCHED.read().clone();