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589 lines
18 KiB
Rust
589 lines
18 KiB
Rust
//! Watches subscribed files or directories and routes coarse-grained change
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//! notifications to the subscribers that own matching watched paths.
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use std::collections::BTreeSet;
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use std::collections::HashMap;
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use std::path::Path;
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use std::path::PathBuf;
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use std::sync::Arc;
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use std::sync::Mutex;
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use std::sync::RwLock;
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use std::sync::atomic::AtomicUsize;
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use std::sync::atomic::Ordering;
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use std::time::Duration;
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use notify::Event;
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use notify::EventKind;
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use notify::RecommendedWatcher;
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use notify::RecursiveMode;
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use notify::Watcher;
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use tokio::runtime::Handle;
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use tokio::sync::Mutex as AsyncMutex;
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use tokio::sync::Notify;
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use tokio::sync::mpsc;
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use tokio::time::Instant;
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use tokio::time::sleep_until;
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use tracing::warn;
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#[derive(Debug, Clone, PartialEq, Eq)]
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/// Coalesced file change notification for a subscriber.
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pub struct FileWatcherEvent {
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/// Changed paths delivered in sorted order with duplicates removed.
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pub paths: Vec<PathBuf>,
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}
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#[derive(Clone, Debug, Eq, Hash, PartialEq)]
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/// Path subscription registered by a [`FileWatcherSubscriber`].
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pub struct WatchPath {
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/// Root path to watch.
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pub path: PathBuf,
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/// Whether events below `path` should match recursively.
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pub recursive: bool,
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}
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type SubscriberId = u64;
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#[derive(Default)]
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struct WatchState {
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next_subscriber_id: SubscriberId,
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path_ref_counts: HashMap<PathBuf, PathWatchCounts>,
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subscribers: HashMap<SubscriberId, SubscriberState>,
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}
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struct SubscriberState {
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watched_paths: HashMap<WatchPath, usize>,
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tx: WatchSender,
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}
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/// Receives coalesced change notifications for a single subscriber.
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pub struct Receiver {
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inner: Arc<ReceiverInner>,
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}
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struct WatchSender {
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inner: Arc<ReceiverInner>,
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}
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struct ReceiverInner {
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changed_paths: AsyncMutex<BTreeSet<PathBuf>>,
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notify: Notify,
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sender_count: AtomicUsize,
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}
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impl Receiver {
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/// Waits for the next batch of changed paths, or returns `None` once the
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/// corresponding subscriber has been removed and no more events can arrive.
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pub async fn recv(&mut self) -> Option<FileWatcherEvent> {
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loop {
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let notified = self.inner.notify.notified();
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{
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let mut changed_paths = self.inner.changed_paths.lock().await;
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if !changed_paths.is_empty() {
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return Some(FileWatcherEvent {
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paths: std::mem::take(&mut *changed_paths).into_iter().collect(),
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});
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}
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if self.inner.sender_count.load(Ordering::Acquire) == 0 {
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return None;
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}
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}
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notified.await;
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}
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}
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}
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impl WatchSender {
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async fn add_changed_paths(&self, paths: &[PathBuf]) {
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if paths.is_empty() {
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return;
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}
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let mut changed_paths = self.inner.changed_paths.lock().await;
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let previous_len = changed_paths.len();
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changed_paths.extend(paths.iter().cloned());
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if changed_paths.len() != previous_len {
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self.inner.notify.notify_one();
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}
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}
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}
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impl Clone for WatchSender {
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fn clone(&self) -> Self {
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self.inner.sender_count.fetch_add(1, Ordering::Relaxed);
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Self {
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inner: Arc::clone(&self.inner),
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}
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}
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}
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impl Drop for WatchSender {
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fn drop(&mut self) {
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if self.inner.sender_count.fetch_sub(1, Ordering::AcqRel) == 1 {
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self.inner.notify.notify_waiters();
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}
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}
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}
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fn watch_channel() -> (WatchSender, Receiver) {
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let inner = Arc::new(ReceiverInner {
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changed_paths: AsyncMutex::new(BTreeSet::new()),
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notify: Notify::new(),
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sender_count: AtomicUsize::new(1),
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});
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(
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WatchSender {
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inner: Arc::clone(&inner),
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},
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Receiver { inner },
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)
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}
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#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
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struct PathWatchCounts {
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non_recursive: usize,
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recursive: usize,
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}
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impl PathWatchCounts {
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fn increment(&mut self, recursive: bool, amount: usize) {
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if recursive {
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self.recursive += amount;
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} else {
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self.non_recursive += amount;
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}
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}
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fn decrement(&mut self, recursive: bool, amount: usize) {
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if recursive {
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self.recursive = self.recursive.saturating_sub(amount);
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} else {
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self.non_recursive = self.non_recursive.saturating_sub(amount);
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}
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}
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fn effective_mode(self) -> Option<RecursiveMode> {
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if self.recursive > 0 {
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Some(RecursiveMode::Recursive)
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} else if self.non_recursive > 0 {
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Some(RecursiveMode::NonRecursive)
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} else {
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None
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}
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}
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fn is_empty(self) -> bool {
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self.non_recursive == 0 && self.recursive == 0
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}
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}
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struct FileWatcherInner {
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watcher: RecommendedWatcher,
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watched_paths: HashMap<PathBuf, RecursiveMode>,
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}
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/// Coalesces bursts of watch notifications and emits at most once per interval.
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pub struct ThrottledWatchReceiver {
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rx: Receiver,
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interval: Duration,
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next_allowed: Option<Instant>,
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}
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impl ThrottledWatchReceiver {
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/// Creates a throttling wrapper around a raw watcher [`Receiver`].
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pub fn new(rx: Receiver, interval: Duration) -> Self {
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Self {
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rx,
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interval,
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next_allowed: None,
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}
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}
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/// Receives the next event, enforcing the configured minimum delay after
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/// the previous emission.
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pub async fn recv(&mut self) -> Option<FileWatcherEvent> {
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if let Some(next_allowed) = self.next_allowed {
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sleep_until(next_allowed).await;
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}
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let event = self.rx.recv().await;
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if event.is_some() {
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self.next_allowed = Some(Instant::now() + self.interval);
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}
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event
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}
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}
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/// Handle used to register watched paths for one logical consumer.
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pub struct FileWatcherSubscriber {
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id: SubscriberId,
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file_watcher: Arc<FileWatcher>,
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}
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impl FileWatcherSubscriber {
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/// Registers the provided paths for this subscriber and returns an RAII
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/// guard that unregisters them on drop.
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pub fn register_paths(&self, watched_paths: Vec<WatchPath>) -> WatchRegistration {
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let watched_paths = dedupe_watched_paths(watched_paths);
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self.file_watcher.register_paths(self.id, &watched_paths);
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WatchRegistration {
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file_watcher: Arc::downgrade(&self.file_watcher),
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subscriber_id: self.id,
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watched_paths,
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}
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}
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#[cfg(test)]
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pub(crate) fn register_path(&self, path: PathBuf, recursive: bool) -> WatchRegistration {
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self.register_paths(vec![WatchPath { path, recursive }])
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}
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}
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impl Drop for FileWatcherSubscriber {
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fn drop(&mut self) {
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self.file_watcher.remove_subscriber(self.id);
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}
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}
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/// RAII guard for a set of active path registrations.
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pub struct WatchRegistration {
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file_watcher: std::sync::Weak<FileWatcher>,
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subscriber_id: SubscriberId,
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watched_paths: Vec<WatchPath>,
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}
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impl Default for WatchRegistration {
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fn default() -> Self {
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Self {
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file_watcher: std::sync::Weak::new(),
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subscriber_id: 0,
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watched_paths: Vec::new(),
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}
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}
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}
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impl Drop for WatchRegistration {
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fn drop(&mut self) {
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if let Some(file_watcher) = self.file_watcher.upgrade() {
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file_watcher.unregister_paths(self.subscriber_id, &self.watched_paths);
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}
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}
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}
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/// Multi-subscriber file watcher built on top of `notify`.
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pub struct FileWatcher {
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inner: Option<Mutex<FileWatcherInner>>,
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state: Arc<RwLock<WatchState>>,
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}
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impl FileWatcher {
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/// Creates a live filesystem watcher and starts its background event loop
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/// on the current Tokio runtime.
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pub fn new() -> notify::Result<Self> {
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let (raw_tx, raw_rx) = mpsc::unbounded_channel();
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let raw_tx_clone = raw_tx;
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let watcher = notify::recommended_watcher(move |res| {
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let _ = raw_tx_clone.send(res);
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})?;
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let inner = FileWatcherInner {
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watcher,
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watched_paths: HashMap::new(),
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};
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let state = Arc::new(RwLock::new(WatchState::default()));
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let file_watcher = Self {
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inner: Some(Mutex::new(inner)),
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state,
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};
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file_watcher.spawn_event_loop(raw_rx);
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Ok(file_watcher)
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}
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/// Creates an inert watcher that only supports test-driven synthetic
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/// notifications.
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pub fn noop() -> Self {
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Self {
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inner: None,
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state: Arc::new(RwLock::new(WatchState::default())),
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}
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}
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/// Adds a new subscriber and returns both its registration handle and its
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/// dedicated event receiver.
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pub fn add_subscriber(self: &Arc<Self>) -> (FileWatcherSubscriber, Receiver) {
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let (tx, rx) = watch_channel();
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let mut state = self
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.state
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.write()
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.unwrap_or_else(std::sync::PoisonError::into_inner);
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let subscriber_id = state.next_subscriber_id;
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state.next_subscriber_id += 1;
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state.subscribers.insert(
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subscriber_id,
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SubscriberState {
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watched_paths: HashMap::new(),
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tx,
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},
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);
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let subscriber = FileWatcherSubscriber {
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id: subscriber_id,
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file_watcher: self.clone(),
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};
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(subscriber, rx)
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}
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fn register_paths(&self, subscriber_id: SubscriberId, watched_paths: &[WatchPath]) {
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let mut state = self
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.state
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.write()
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.unwrap_or_else(std::sync::PoisonError::into_inner);
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let mut inner_guard: Option<std::sync::MutexGuard<'_, FileWatcherInner>> = None;
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for watched_path in watched_paths {
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{
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let Some(subscriber) = state.subscribers.get_mut(&subscriber_id) else {
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return;
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};
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*subscriber
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.watched_paths
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.entry(watched_path.clone())
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.or_default() += 1;
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}
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let counts = state
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.path_ref_counts
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.entry(watched_path.path.clone())
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.or_default();
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let previous_mode = counts.effective_mode();
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counts.increment(watched_path.recursive, /*amount*/ 1);
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let next_mode = counts.effective_mode();
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if previous_mode != next_mode {
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self.reconfigure_watch(&watched_path.path, next_mode, &mut inner_guard);
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}
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}
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}
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// Bridge `notify`'s callback-based events into the Tokio runtime and
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// notify the matching subscribers.
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fn spawn_event_loop(&self, mut raw_rx: mpsc::UnboundedReceiver<notify::Result<Event>>) {
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if let Ok(handle) = Handle::try_current() {
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let state = Arc::clone(&self.state);
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handle.spawn(async move {
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loop {
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match raw_rx.recv().await {
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Some(Ok(event)) => {
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if !is_mutating_event(&event) {
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continue;
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}
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if event.paths.is_empty() {
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continue;
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}
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Self::notify_subscribers(&state, &event.paths).await;
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}
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Some(Err(err)) => {
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warn!("file watcher error: {err}");
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}
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None => break,
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}
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}
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});
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} else {
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warn!("file watcher loop skipped: no Tokio runtime available");
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}
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}
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fn unregister_paths(&self, subscriber_id: SubscriberId, watched_paths: &[WatchPath]) {
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let mut state = self
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.state
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.write()
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.unwrap_or_else(std::sync::PoisonError::into_inner);
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let mut inner_guard: Option<std::sync::MutexGuard<'_, FileWatcherInner>> = None;
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for watched_path in watched_paths {
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{
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let Some(subscriber) = state.subscribers.get_mut(&subscriber_id) else {
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return;
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};
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let Some(subscriber_count) = subscriber.watched_paths.get_mut(watched_path) else {
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continue;
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};
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*subscriber_count = subscriber_count.saturating_sub(1);
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if *subscriber_count == 0 {
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subscriber.watched_paths.remove(watched_path);
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}
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}
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let Some(counts) = state.path_ref_counts.get_mut(&watched_path.path) else {
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continue;
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};
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let previous_mode = counts.effective_mode();
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counts.decrement(watched_path.recursive, /*amount*/ 1);
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let next_mode = counts.effective_mode();
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if counts.is_empty() {
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state.path_ref_counts.remove(&watched_path.path);
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}
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if previous_mode != next_mode {
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self.reconfigure_watch(&watched_path.path, next_mode, &mut inner_guard);
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}
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}
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}
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fn remove_subscriber(&self, subscriber_id: SubscriberId) {
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let mut state = self
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.state
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.write()
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.unwrap_or_else(std::sync::PoisonError::into_inner);
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let Some(subscriber) = state.subscribers.remove(&subscriber_id) else {
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return;
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};
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let mut inner_guard: Option<std::sync::MutexGuard<'_, FileWatcherInner>> = None;
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for (watched_path, count) in subscriber.watched_paths {
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let Some(path_counts) = state.path_ref_counts.get_mut(&watched_path.path) else {
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continue;
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};
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let previous_mode = path_counts.effective_mode();
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path_counts.decrement(watched_path.recursive, count);
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let next_mode = path_counts.effective_mode();
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if path_counts.is_empty() {
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state.path_ref_counts.remove(&watched_path.path);
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}
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if previous_mode != next_mode {
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self.reconfigure_watch(&watched_path.path, next_mode, &mut inner_guard);
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}
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}
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}
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fn reconfigure_watch<'a>(
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&'a self,
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path: &Path,
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next_mode: Option<RecursiveMode>,
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inner_guard: &mut Option<std::sync::MutexGuard<'a, FileWatcherInner>>,
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) {
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let Some(inner) = &self.inner else {
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return;
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};
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if inner_guard.is_none() {
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let guard = inner
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.lock()
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.unwrap_or_else(std::sync::PoisonError::into_inner);
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*inner_guard = Some(guard);
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}
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let Some(guard) = inner_guard.as_mut() else {
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return;
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};
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let existing_mode = guard.watched_paths.get(path).copied();
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if existing_mode == next_mode {
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return;
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}
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if existing_mode.is_some() {
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if let Err(err) = guard.watcher.unwatch(path) {
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warn!("failed to unwatch {}: {err}", path.display());
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}
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guard.watched_paths.remove(path);
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}
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let Some(next_mode) = next_mode else {
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return;
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};
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if !path.exists() {
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return;
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}
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if let Err(err) = guard.watcher.watch(path, next_mode) {
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warn!("failed to watch {}: {err}", path.display());
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return;
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}
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guard.watched_paths.insert(path.to_path_buf(), next_mode);
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}
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async fn notify_subscribers(state: &RwLock<WatchState>, event_paths: &[PathBuf]) {
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let subscribers_to_notify: Vec<(WatchSender, Vec<PathBuf>)> = {
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let state = state
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.read()
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.unwrap_or_else(std::sync::PoisonError::into_inner);
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state
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.subscribers
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.values()
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.filter_map(|subscriber| {
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let changed_paths: Vec<PathBuf> = event_paths
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.iter()
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.filter(|event_path| {
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subscriber.watched_paths.keys().any(|watched_path| {
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watch_path_matches_event(watched_path, event_path)
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})
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})
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.cloned()
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.collect();
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(!changed_paths.is_empty()).then_some((subscriber.tx.clone(), changed_paths))
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})
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.collect()
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};
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for (subscriber, changed_paths) in subscribers_to_notify {
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subscriber.add_changed_paths(&changed_paths).await;
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}
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}
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#[cfg(test)]
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pub(crate) async fn send_paths_for_test(&self, paths: Vec<PathBuf>) {
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Self::notify_subscribers(&self.state, &paths).await;
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}
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#[cfg(test)]
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pub(crate) fn spawn_event_loop_for_test(
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&self,
|
|
raw_rx: mpsc::UnboundedReceiver<notify::Result<Event>>,
|
|
) {
|
|
self.spawn_event_loop(raw_rx);
|
|
}
|
|
|
|
#[cfg(test)]
|
|
pub(crate) fn watch_counts_for_test(&self, path: &Path) -> Option<(usize, usize)> {
|
|
let state = self
|
|
.state
|
|
.read()
|
|
.unwrap_or_else(std::sync::PoisonError::into_inner);
|
|
state
|
|
.path_ref_counts
|
|
.get(path)
|
|
.map(|counts| (counts.non_recursive, counts.recursive))
|
|
}
|
|
}
|
|
|
|
fn is_mutating_event(event: &Event) -> bool {
|
|
matches!(
|
|
event.kind,
|
|
EventKind::Create(_) | EventKind::Modify(_) | EventKind::Remove(_)
|
|
)
|
|
}
|
|
|
|
fn dedupe_watched_paths(mut watched_paths: Vec<WatchPath>) -> Vec<WatchPath> {
|
|
watched_paths.sort_unstable_by(|a, b| {
|
|
a.path
|
|
.as_os_str()
|
|
.cmp(b.path.as_os_str())
|
|
.then(a.recursive.cmp(&b.recursive))
|
|
});
|
|
watched_paths.dedup();
|
|
watched_paths
|
|
}
|
|
|
|
fn watch_path_matches_event(watched_path: &WatchPath, event_path: &Path) -> bool {
|
|
if event_path == watched_path.path {
|
|
return true;
|
|
}
|
|
if watched_path.path.starts_with(event_path) {
|
|
return true;
|
|
}
|
|
if !event_path.starts_with(&watched_path.path) {
|
|
return false;
|
|
}
|
|
watched_path.recursive || event_path.parent() == Some(watched_path.path.as_path())
|
|
}
|
|
|
|
#[cfg(test)]
|
|
#[path = "file_watcher_tests.rs"]
|
|
mod tests;
|