FileSystemWatcher issues when running dnx-watch on Mono

[miguellira]

Running dnx-watch against a simple web application on Mono works fine.

However, given the known limitations of FileSystemWatcher in Mono (dotnet/aspnetcore#508, dotnet/aspnetcore#554) the only way I've managed to run a reasonably sized web application is to set MONO_MANAGED_WATCHER="disabled"

Having this environment variable set appears to disables dnx-watch, however, unsetting the variable produces the following error:

Miguels-MBP:WebApp miguellira$ dnx-watch kestrel
[DnxWatcher] info: Running dnx with the following arguments: --project /Users/miguellira/Sandbox/WebApp/project.json kestrel
[DnxWatcher] info: dnx process id: 8610
/Users/miguellira/.dnx/runtimes/dnx-mono.1.0.0-beta8-15736/bin/dnx: line 9: pwd: write error: Broken pipe
System.IO.IOException: kqueue() FileSystemWatcher has reached the maximum number of files to watch.
   at System.IO.KqueueMonitor.Start () in <filename unknown>:line 0
   at System.IO.KeventWatcher.StartDispatching (System.IO.FileSystemWatcher fsw) in <filename unknown>:line 0
   at System.IO.FileSystemWatcher.Start () in <filename unknown>:line 0
   at System.IO.FileSystemWatcher.set_EnableRaisingEvents (Boolean value) in <filename unknown>:line 0
   at (wrapper remoting-invoke-with-check) System.IO.FileSystemWatcher:set_EnableRaisingEvents (bool)
   at Microsoft.Dnx.Watcher.Core.FileWatcher.AddWatcher (System.String path) in <filename unknown>:line 0
   at Microsoft.Dnx.Watcher.Core.FileWatcher..ctor (System.String path) in <filename unknown>:line 0
   at Microsoft.Dnx.Watcher.Core.DnxWatcher+<>c.<CreateDefault>b__13_0 (System.String root) in <filename unknown>:line 0
   at Microsoft.Dnx.Watcher.Core.DnxWatcher+<WaitForProjectFileToChangeAsync>d__7.MoveNext () in <filename unknown>:line 0

Is dnx-watch not recommended for use with Mono until that bug is addressed?

[muratg]

@victorhurdugaci is this known issue in Mono? If so, can we track it in the External repo, and close this one?

cc @moozzyk

[victorhurdugaci]

It is a known mono issue: https://bugzilla.xamarin.com/show_bug.cgi?id=28693

@miguellira how many files does your app have?

[miguellira]

@victorhurdugaci Not many. I haven't tried to figure out the limit but as you know npm modules tend to have huge directory trees.

For now, I simply delete the node_modules, bower_components, and tidy up my target lib folder via a gulp task post restore and I can run dnx-watch.

[muratg]

@miguellira I'm glad you're able to work around it although it's not an ideal solution. Feel free to push the Mono bug to resolution :)

@victorhurdugaci Cool, please file an External to track the Mono bug and close this one.

[nathanielcook]

In my case it was the .git folder that was causing the problem. I moved my code into a src folder and ran dnx-watch there instead of the main root, and that works fine (since src doesn't include the .git folder).

[victorhurdugaci]

@nathanielcook not sure how that would cause an issue. Can you give more details about the folder structure that you have before it started working and what command were you running?

[nathanielcook]

Before

projectroot
  .git
  Controllers
  Models
  Views
  project.json
  project.lock.json
  Properties
  Startup.cs
  wwwroot
  LICENSE
  README.md

After

projectroot
  .git
  LICENSE
  README
  src
    Models
    Controllers
    Views
    etc

Before I was running dnx-watch in projectroot. Now I am running dnx-watch in projectroot/src. Make sense?

[victorhurdugaci]

ohhh... yes, that could be a problem on Mono because of the limit that @miguellira mentioned. The .git folder could have lots of files in it.

[victorhurdugaci]

Btw, can you try running on CoreCLR?

[nathanielcook]

I'm not sure what that means.

[victorhurdugaci]

dnx-watch runs on the same CLR as your project. On Linux we have Mono and CoreCLR. If your project supports CoreCLR (aka it has the dnxcore50 target) you can try running on it. You shouldn't hit the file limit.

Instructions on how to install CoreCLR on Linux: https://docs.asp.net/en/latest/getting-started/installing-on-linux.html

Then dnvm use -r CoreCLR

And then the watcher will use the active CoreCLR runtime.

[miguellira]

@nathanielcook Yeah, you should always consider initializing git on your project root. BTW, as soon as you exceed 200 files/folders in the folder you run dnx-watch web it will barf.

It all boils down to this line in Mono:
https://github.com/mono/mono/blob/b7a308f660de8174b64697a422abfc7315d07b8c/mcs/class/System/System.IO/KeventWatcher.cs#L444

It seems as though 200 is the magic #:
https://github.com/mono/mono/blob/b7a308f660de8174b64697a422abfc7315d07b8c/mcs/class/System/System.IO/KeventWatcher.cs#L641

I'm sure the Mono guys know why since that bug is still outstanding.

[miguellira]

@victorhurdugaci For the record, dnx-watch indeed runs without limitation on dnxcore50. Unfortunately, if you have a dependency that requires dnx451 you're stuck with mono and the 200 file limit.

[muratg]

@miguellira Could you add this information to the Mono bug report (if it's not already there)?

I suspect they haven't investigated this bug yet, but since you already seem to have found the root cause, I'm sure they would appreciate the input :)

[miguellira]

@muratg Done. I've updated the bug with my findings.