FileSystemWatcher doesn't trigger Deleted event for file when watched directory is deleted on OSX

[ericstj]

Description

Create a FileSystemWatcher that watches a directory.
Create a file in that directory and observe Created event.
Delete the file and observe Deleted event.
Create another file in that directory and observe Created event.
Delete the directory, and no deleted event ever arrives.

Configuration

• Which version of .NET is the code running on? .NET 5.0
• What OS and version, and what distro if applicable? OSX 10.13.6
• What is the architecture (x64, x86, ARM, ARM64)? x64
• Do you know whether it is specific to that configuration? It appears to be specific to OSX

Regression?

Not a regression, but different than other platforms

Other information

May be similar to #30415
Discovered when working on #41426

Repro:

using System;
using System.IO;
using System.Threading.Tasks;


namespace fileWatch
{
    class Program
    {
        static async Task Main(string[] args)
        {
            int waitTime = 1000;
            var rootPath = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName());
            var subDir = Path.Combine(rootPath, "sub");
            
            Directory.CreateDirectory(rootPath);
            Directory.CreateDirectory(subDir);

            using (var fsw = new FileSystemWatcher(rootPath, "*"))
            {
                fsw.Created += (o, e) => Console.WriteLine($"Created {e.FullPath}");
                fsw.Deleted += (o, e) => Console.WriteLine($"Deleted {e.FullPath}");
                fsw.IncludeSubdirectories = true;
                fsw.EnableRaisingEvents = true;

                var fileLocation = Path.Combine(subDir, Path.GetRandomFileName());
                File.WriteAllText(fileLocation, "temp");
                await Task.Delay(waitTime);
                File.Delete(fileLocation);
                await Task.Delay(waitTime);

                fileLocation = Path.Combine(subDir, Path.GetRandomFileName());
                File.WriteAllText(fileLocation, "temp");
                await Task.Delay(waitTime);
                Directory.Delete(subDir, true);
                await Task.Delay(waitTime);

                fileLocation = Path.Combine(rootPath, Path.GetRandomFileName());
                File.WriteAllText(fileLocation, "temp");
                await Task.Delay(waitTime);
                File.Delete(fileLocation);
                await Task.Delay(waitTime);

                fileLocation = Path.Combine(rootPath, Path.GetRandomFileName());
                File.WriteAllText(fileLocation, "temp");
                await Task.Delay(waitTime);
                Directory.Delete(rootPath, true);
                await Task.Delay(waitTime);
                Console.WriteLine(File.Exists(fileLocation));
            }
        }
    }
}

[ericstj]

This appears to be unique to only when the root-level watched directory is removed. If a directory underneath the root directory is removed then the deleted event is observed. I've updated the sample above to better illustrate this.

[carlossanlop]

Delete the directory, and no deleted event ever arrives.

It was my understanding that FileSystemWatcher does not watch changes in the monitored directory itself, only on the files and directories inside it.

I remembered that fact from this closed issue, from which I learned that not even Windows reports events from the monitored directory itself. That is how the behavior is described in the Windows API we invoke: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-readdirectorychangesw

[jozkee]

Not a regression, but different than other platforms

@ericstj the sample you provided behaves similar to what you describe on Windows and Linux, is there something that I am missing?
This is the output that I get:

Created C:\Users\dacantu\AppData\Local\Temp\rr05f1lh.mdy\sub\4fo3tpfq.nwd
Deleted C:\Users\dacantu\AppData\Local\Temp\rr05f1lh.mdy\sub\4fo3tpfq.nwd
Created C:\Users\dacantu\AppData\Local\Temp\rr05f1lh.mdy\sub\pboshy2t.kar
Deleted C:\Users\dacantu\AppData\Local\Temp\rr05f1lh.mdy\sub\pboshy2t.kar
Deleted C:\Users\dacantu\AppData\Local\Temp\rr05f1lh.mdy\sub
Created C:\Users\dacantu\AppData\Local\Temp\rr05f1lh.mdy\k2lg0a3p.kyq
Deleted C:\Users\dacantu\AppData\Local\Temp\rr05f1lh.mdy\k2lg0a3p.kyq
Created C:\Users\dacantu\AppData\Local\Temp\rr05f1lh.mdy\2mjivqn4.qf5
Deleted C:\Users\dacantu\AppData\Local\Temp\rr05f1lh.mdy\2mjivqn4.qf5
False

[ericstj]

This failure is specific to Mac (OSX) which uses a different implementation. On Mac the last deleted event will be missing.

[jozkee]

I see now, it is reporting Create twice and not reporting Delete when you erase the root as you mentioned:

Created /var/folders/gz/6z3dn8kn20g5wlk7rt7cs0h40000gq/T/xltqrcpx.vdv/sub/noozqidc.ibi
Created /var/folders/gz/6z3dn8kn20g5wlk7rt7cs0h40000gq/T/xltqrcpx.vdv/sub/noozqidc.ibi
Deleted /var/folders/gz/6z3dn8kn20g5wlk7rt7cs0h40000gq/T/xltqrcpx.vdv/sub/noozqidc.ibi
Created /var/folders/gz/6z3dn8kn20g5wlk7rt7cs0h40000gq/T/xltqrcpx.vdv/sub/ibmlfqwy.nie
Created /var/folders/gz/6z3dn8kn20g5wlk7rt7cs0h40000gq/T/xltqrcpx.vdv/sub/ibmlfqwy.nie
Deleted /var/folders/gz/6z3dn8kn20g5wlk7rt7cs0h40000gq/T/xltqrcpx.vdv/sub/ibmlfqwy.nie
Created /var/folders/gz/6z3dn8kn20g5wlk7rt7cs0h40000gq/T/xltqrcpx.vdv/sub
Deleted /var/folders/gz/6z3dn8kn20g5wlk7rt7cs0h40000gq/T/xltqrcpx.vdv/sub
Created /var/folders/gz/6z3dn8kn20g5wlk7rt7cs0h40000gq/T/xltqrcpx.vdv/xbdmmr50.et3
Created /var/folders/gz/6z3dn8kn20g5wlk7rt7cs0h40000gq/T/xltqrcpx.vdv/xbdmmr50.et3
Deleted /var/folders/gz/6z3dn8kn20g5wlk7rt7cs0h40000gq/T/xltqrcpx.vdv/xbdmmr50.et3
Created /var/folders/gz/6z3dn8kn20g5wlk7rt7cs0h40000gq/T/xltqrcpx.vdv/xxfnco43.dmg
False