fix: share inotify fd across watchers (#26200)

Fixes https://github.com/denoland/deno/issues/26104
Fixes https://github.com/denoland/deno/issues/26071
Fixes https://github.com/denoland/deno/issues/17757

Cargo.lock

@@ -2042,6 +2042,7 @@ dependencies = [
  "percent-encoding",
  "regex",
  "rustyline",
+ "same-file",
  "serde",
  "signal-hook",
  "signal-hook-registry",

runtime/Cargo.toml

@@ -117,6 +117,7 @@ once_cell.workspace = true
 percent-encoding.workspace = true
 regex.workspace = true
 rustyline = { workspace = true, features = ["custom-bindings"] }
+same-file = "1.0.6"
 serde.workspace = true
 signal-hook = "0.3.17"
 signal-hook-registry = "1.4.0"

runtime/js/40_fs_events.js

@@ -21,7 +21,7 @@ class FsWatcher {
 
   constructor(paths, options) {
     const { recursive } = options;
-    this.#rid = op_fs_events_open({ recursive, paths });
+    this.#rid = op_fs_events_open(recursive, paths);
   }
 
   unref() {

runtime/ops/fs_events.rs

@@ -19,13 +19,14 @@ use notify::EventKind;
 use notify::RecommendedWatcher;
 use notify::RecursiveMode;
 use notify::Watcher;
-use serde::Deserialize;
 use serde::Serialize;
 use std::borrow::Cow;
 use std::cell::RefCell;
 use std::convert::From;
+use std::path::Path;
 use std::path::PathBuf;
 use std::rc::Rc;
+use std::sync::Arc;
 use tokio::sync::mpsc;
 
 deno_core::extension!(
@@ -34,8 +35,6 @@ deno_core::extension!(
 );
 
 struct FsEventsResource {
-  #[allow(unused)]
-  watcher: RecommendedWatcher,
   receiver: AsyncRefCell<mpsc::Receiver<Result<FsEvent, NotifyError>>>,
   cancel: CancelHandle,
 }
@@ -58,7 +57,7 @@ impl Resource for FsEventsResource {
 ///
 /// Feel free to expand this struct as long as you can add tests to demonstrate
 /// the complexity.
-#[derive(Serialize, Debug)]
+#[derive(Serialize, Debug, Clone)]
 struct FsEvent {
   kind: &'static str,
   paths: Vec<PathBuf>,
@@ -92,6 +91,24 @@ impl From<NotifyEvent> for FsEvent {
   }
 }
 
+type WatchSender = (Vec<String>, mpsc::Sender<Result<FsEvent, NotifyError>>);
+
+struct WatcherState {
+  senders: Arc<Mutex<Vec<WatchSender>>>,
+  watcher: RecommendedWatcher,
+}
+
+fn starts_with_canonicalized(path: &Path, prefix: &str) -> bool {
+  #[allow(clippy::disallowed_methods)]
+  let path = path.canonicalize().ok();
+  #[allow(clippy::disallowed_methods)]
+  let prefix = std::fs::canonicalize(prefix).ok();
+  match (path, prefix) {
+    (Some(path), Some(prefix)) => path.starts_with(prefix),
+    _ => false,
+  }
+}
+
 #[derive(Debug, thiserror::Error)]
 pub enum FsEventsError {
   #[error(transparent)]
@@ -104,44 +121,73 @@ pub enum FsEventsError {
   Canceled(#[from] deno_core::Canceled),
 }
 
-#[derive(Deserialize)]
-pub struct OpenArgs {
-  recursive: bool,
+fn start_watcher(
+  state: &mut OpState,
   paths: Vec<String>,
+  sender: mpsc::Sender<Result<FsEvent, NotifyError>>,
+) -> Result<(), FsEventsError> {
+  if let Some(watcher) = state.try_borrow_mut::<WatcherState>() {
+    watcher.senders.lock().push((paths, sender));
+    return Ok(());
+  }
+
+  let senders = Arc::new(Mutex::new(vec![(paths, sender)]));
+
+  let sender_clone = senders.clone();
+  let watcher: RecommendedWatcher = Watcher::new(
+    move |res: Result<NotifyEvent, NotifyError>| {
+      let res2 = res.map(FsEvent::from).map_err(FsEventsError::Notify);
+      for (paths, sender) in sender_clone.lock().iter() {
+        // Ignore result, if send failed it means that watcher was already closed,
+        // but not all messages have been flushed.
+
+        // Only send the event if the path matches one of the paths that the user is watching
+        if let Ok(event) = &res2 {
+          if paths.iter().any(|path| {
+            event.paths.iter().any(|event_path| {
+              same_file::is_same_file(event_path, path).unwrap_or(false)
+                || starts_with_canonicalized(event_path, path)
+            })
+          }) {
+            let _ = sender.try_send(Ok(event.clone()));
+          }
+        }
+      }
+    },
+    Default::default(),
+  )?;
+
+  state.put::<WatcherState>(WatcherState { watcher, senders });
+
+  Ok(())
 }
 
 #[op2]
 #[smi]
 fn op_fs_events_open(
   state: &mut OpState,
-  #[serde] args: OpenArgs,
+  recursive: bool,
+  #[serde] paths: Vec<String>,
 ) -> Result<ResourceId, FsEventsError> {
   let (sender, receiver) = mpsc::channel::<Result<FsEvent, NotifyError>>(16);
-  let sender = Mutex::new(sender);
-  let mut watcher: RecommendedWatcher = Watcher::new(
-    move |res: Result<NotifyEvent, NotifyError>| {
-      let res2 = res.map(FsEvent::from);
-      let sender = sender.lock();
-      // Ignore result, if send failed it means that watcher was already closed,
-      // but not all messages have been flushed.
-      let _ = sender.try_send(res2);
-    },
-    Default::default(),
-  )?;
-  let recursive_mode = if args.recursive {
+
+  start_watcher(state, paths.clone(), sender)?;
+
+  let recursive_mode = if recursive {
     RecursiveMode::Recursive
   } else {
     RecursiveMode::NonRecursive
   };
-  for path in &args.paths {
+  for path in &paths {
     let path = state
       .borrow_mut::<PermissionsContainer>()
       .check_read(path, "Deno.watchFs()")
       .map_err(FsEventsError::Permission)?;
-    watcher.watch(&path, recursive_mode)?;
+
+    let watcher = state.borrow_mut::<WatcherState>();
+    watcher.watcher.watch(&path, recursive_mode)?;
   }
   let resource = FsEventsResource {
-    watcher,
     receiver: AsyncRefCell::new(receiver),
     cancel: Default::default(),
   };