Release v0.2.1: fix watcher idle CPU feedback loop

CHANGELOG.md

@@ -1,5 +1,14 @@
 # Changelog
 
+## 0.2.1
+
+- Fix high idle watcher CPU usage caused by directory scans generating filesystem open events and triggering further scans.
+- Ignore read/open access events before queuing watcher work, while retaining write-close events and filesystem overflow recovery.
+- Batch queued filesystem events into one scan while preserving periodic reconciliation and partial-download retries.
+- Add a Linux idle CPU regression check alongside the download, rename, duplicate and restart integration checks.
+
+Validation: 59 automated tests, Clippy, formatting, and release build passed. Local Linux idle profiling confirmed the watcher no longer continuously rescans its download directory.
+
 ## 0.2.0
 
 - Import components into global or portable project libraries, creating and registering libraries when needed.

Cargo.lock

@@ -2869,7 +2869,7 @@ checksum = "ebc1c04c71510c7f702b52b7c350734c9ff1295c464a03335b00bb84fc54f853"
 
 [[package]]
 name = "uniloader"
-version = "0.2.0"
+version = "0.2.1"
 dependencies = [
  "anyhow",
  "chrono",

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "uniloader"
-version = "0.2.0"
+version = "0.2.1"
 edition = "2024"
 rust-version = "1.95"
 

src/main.rs

@@ -17,7 +17,10 @@ use anyhow::{Context, Result, bail};
 use clap::{Parser, Subcommand};
 use config::Config;
 use importer::{Request, Session};
-use notify::{RecursiveMode, Watcher};
+use notify::{
+    Event, EventKind, RecursiveMode, Watcher,
+    event::{AccessKind, AccessMode},
+};
 use std::{
     collections::{BTreeMap, BTreeSet},
     fs,
@@ -141,10 +144,25 @@ fn complete_zip(p: &Path) -> Result<bool> {
     }
     Ok(supported)
 }
+fn event_requires_scan(event: &Event) -> bool {
+    // Reading a watched directory emits OPEN events on Linux, including from
+    // our own scans. Only a writer closing a file can make access relevant.
+    event.need_rescan()
+        || !matches!(event.kind, EventKind::Access(_))
+        || matches!(
+            event.kind,
+            EventKind::Access(AccessKind::Close(AccessMode::Write))
+        )
+}
 fn watch(cfg: Config, noninteractive: bool) -> Result<()> {
     let _watch_lock = storage::Lock::watcher()?;
     let (events_tx, events_rx) = mpsc::channel();
-    let mut watcher = notify::recommended_watcher(events_tx)?;
+    let mut watcher = notify::recommended_watcher(move |event: notify::Result<Event>| {
+        // Filter before queuing so reads cannot keep the receive loop awake.
+        if event.as_ref().map_or(true, event_requires_scan) {
+            let _ = events_tx.send(event);
+        }
+    })?;
     for dir in &cfg.watch.directories {
         if !dir.is_dir() {
             bail!(
@@ -223,8 +241,19 @@ fn watch(cfg: Config, noninteractive: bool) -> Result<()> {
     let mut last_scan = Instant::now();
     loop {
         match events_rx.recv_timeout(Duration::from_millis(500)) {
-            Ok(Ok(_)) => scan(&mut waiting, &seen),
-            Ok(Err(e)) => eprintln!("watch error: {e}"),
+            Ok(event) => {
+                let mut rescan = false;
+                // Bound draining so sustained downloads cannot starve retries.
+                for event in std::iter::once(event).chain(events_rx.try_iter().take(1023)) {
+                    match event {
+                        Ok(_) => rescan = true,
+                        Err(e) => eprintln!("watch error: {e}"),
+                    }
+                }
+                if rescan {
+                    scan(&mut waiting, &seen);
+                }
+            }
             Err(mpsc::RecvTimeoutError::Timeout) => {}
             Err(mpsc::RecvTimeoutError::Disconnected) => bail!("filesystem watcher disconnected"),
         }
@@ -290,6 +319,7 @@ fn watch(cfg: Config, noninteractive: bool) -> Result<()> {
         }
     }
 }
+
 fn main() -> Result<()> {
     let cli = Cli::parse();
     if matches!(cli.command, Some(Commands::Dialog)) {
@@ -375,3 +405,33 @@ fn main() -> Result<()> {
         }
     }
 }
+
+#[cfg(test)]
+mod watch_tests {
+    use super::*;
+    use notify::event::{CreateKind, Flag, ModifyKind, RemoveKind};
+
+    #[test]
+    fn scans_changes_and_write_closes_but_ignores_read_access() {
+        for kind in [
+            EventKind::Any,
+            EventKind::Create(CreateKind::File),
+            EventKind::Modify(ModifyKind::Any),
+            EventKind::Remove(RemoveKind::File),
+            EventKind::Access(AccessKind::Close(AccessMode::Write)),
+        ] {
+            assert!(event_requires_scan(&Event::new(kind)), "{kind:?}");
+        }
+        for kind in [
+            AccessKind::Any,
+            AccessKind::Read,
+            AccessKind::Open(AccessMode::Read),
+            AccessKind::Open(AccessMode::Write),
+            AccessKind::Close(AccessMode::Read),
+        ] {
+            let event = Event::new(EventKind::Access(kind));
+            assert!(!event_requires_scan(&event), "{kind:?}");
+            assert!(event_requires_scan(&event.set_flag(Flag::Rescan)));
+        }
+    }
+}

tests/watch_cli.rs

@@ -124,6 +124,27 @@ fn watcher_handles_partial_and_renamed_downloads_without_blocking_or_reimporting
             .unwrap_or_default()
             .contains("Watching")
     });
+    // Directory scans emit Linux inotify OPEN events themselves. Idle watching
+    // must block instead of repeatedly scanning in response to its own reads.
+    #[cfg(target_os = "linux")]
+    {
+        let runtime = || {
+            fs::read_to_string(format!("/proc/{}/schedstat", watcher.0.id()))
+                .unwrap()
+                .split_whitespace()
+                .next()
+                .unwrap()
+                .parse::<u64>()
+                .unwrap()
+        };
+        let before = runtime();
+        thread::sleep(Duration::from_secs(1));
+        let cpu = Duration::from_nanos(runtime() - before);
+        assert!(
+            cpu < Duration::from_millis(200),
+            "idle watcher spent {cpu:?} on CPU in one second"
+        );
+    }
     let first = archive("First", 1);
     let second = archive("Independent", 2);
     let third = archive("Renamed", 3);