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FileSystemWatcher on macOS raises no Error when FSEvents drops events: the flags arrive on the watched folder's own path, which is skipped first

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Evaluación

Dificultad
2/5
Tiempo estimado
1-3 horas
Aptitud para principiantes
76/100
Tipo de issue
Error
Claridad
Bien especificado
Estado de actividad
Activo
Stack tecnológico
csharp, macos
Área
backend, operating-systems

Línea de trabajo

Lee src/libraries/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.OSX.cs, especialmente ProcessEvents en torno al salto de la ruta raíz y la llamada a ShouldRescanOccur. Reproduce el problema con la aplicación de consola proporcionada para borrar en ráfaga en macOS y comprueba si los FSEvents descartados activan el evento Error del watcher. Se considera terminado cuando el evento de la ruta raíz que lleva los flags de eventos descartados se notifica como un error y una prueba de regresión cubre ese orden.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

area-System.IO untriaged
Description

On macOS, when more changes arrive at once than FSEvents queues, FSEvents drops events and says so with one event flagged kFSEventStreamEventFlagMustScanSubDirs | kFSEventStreamEventFlagUserDropped (0x3). That event's path is the watched folder itself.

ProcessEvents in FileSystemWatcher.OSX.cs skips every event on the watched folder's own path ("Match Windows and don't notify us about changes to the Root folder") before it calls ShouldRescanOccur. So the dropped-events flags never reach the Error event. The watcher loses changes silently, and its consumer can't tell it should rescan.

Reproduction Steps

A net10.0/net11.0 console app:

using System.Collections.Concurrent;

int count = args.Length > 0 ? int.Parse(args[0]) : 1000;
string folder = Directory.CreateTempSubdirectory("fsw-burst-").FullName;
for (int i = 0; i < count; i++)
{
    File.WriteAllText(Path.Combine(folder, $"F{i}.txt"), "x");
}
Thread.Sleep(1000);

ConcurrentDictionary<string, bool> deleted = new();
int errors = 0;
using FileSystemWatcher watcher = new(folder);
watcher.Deleted += (_, e) => deleted[e.FullPath] = true;
watcher.Error += (_, e) => { Interlocked.Increment(ref errors); Console.WriteLine($"Error: {e.GetException().Message}"); };
watcher.EnableRaisingEvents = true;
Thread.Sleep(1000);

Parallel.For(0, count, i => File.Delete(Path.Combine(folder, $"F{i}.txt")));
Thread.Sleep(5000);
Console.WriteLine($"{Environment.Version}: {count} files deleted, {deleted.Count} Deleted events, {errors} Error events");
Directory.Delete(folder, true);

Output on macOS 27.0.1, Apple Silicon, three runs on each runtime:

10.0.14: 1000 files deleted, 467 Deleted events, 0 Error events
10.0.14: 1000 files deleted, 544 Deleted events, 0 Error events
10.0.14: 1000 files deleted, 488 Deleted events, 0 Error events
11.0.0: 1000 files deleted, 466 Deleted events, 0 Error events
11.0.0: 1000 files deleted, 722 Deleted events, 0 Error events
11.0.0: 1000 files deleted, 1000 Deleted events, 0 Error events

A raw FSEvents stream, created with the flags the watcher uses (FileEvents, NoDefer, WatchRoot; latency 0) and watching the same burst, got 460 events: 459 file removals and one event on the watched folder's own path with flags 0x3. The same happens with IncludeSubdirectories = true and the files in a subfolder: the flagged event is still on the watched folder's path.

Expected behavior

Either a Deleted event for every file, or an Error event saying events were lost.

Actual behavior

About half the deletions are reported, with no Error event.

Regression?

Not known.

Known Workarounds

Treat a burst of changes as possibly lossy, and list again the folders it touched.

Configuration

macOS 27.0.1 (Apple Silicon), .NET 10.0.14 and 11.0.0-rc.3.26522.148.

Other information

Calling ShouldRescanOccur before the root-path skip would fix it. #130637 changes the exception this path raises to InternalBufferOverflowException. Its test reaches the path through a mount in a subfolder, so it doesn't hit this ordering.

Lenguaje dominante
C#
Estrellas
18.4k
Forks
5.8k
Merge medio
2 d 16 h
PR fusionados (30 d)
621

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