The listen gem breaks my laptop

[benaubin]

Steps to reproduce

1. Create a new rails app
2. Run it on a Mac with a bad processor

Expected behavior

My laptop should work fine - processes should stay under the 700-something limit that Apple set.

Actual behavior

When running my Rails app on a Macbook Air with 1.8 ghz of cpu (I know... getting a new computer when they release the new Pro's), I have been getting a "System ran out of resources, can't fork any processes" error in all of my applications (or, they just quietly failed). Finally, I opened Activity Monitor and was able to find more then 500 fsevent_watch processes running (my computer has a maximum of 700 processes total). Doing a Google Search, I stumbled upon the [rb-fsevent gem]. Looking at my Gemfile.lock, I was able to track it down to the listen gem.

I'm unable to tell if it is an issue with the listen gem itself, or @fnx's implementation in Rails (see #22254), but it seems like it's more likely the implementation is broken.

Suggested Fix

I'm unable to tell if it is an issue with the listen gem itself, or @fnx's implementation in Rails (see #22254), but it seems like it's more likely the implementation is broken.

I would make sure that the listen gem is opt-in, especially on systems with low process limits (IIRC, there's a command that allows you to check this).

Temporary Workaround

If your computer is currently showing a "System ran out of resources, can't fork any processes" error, reboot it (logging in and out might work, but I haven't tested that). You probably won't be able to save most of your work (if your software forks a process in order to save).

To remove the gem for a more permanent fix

1. Remove the listen and spring-watcher-listen gems.
2. In your environments/development.rb file, comment out this line:

# Use an evented file watcher to asynchronously detect changes in source code,
# routes, locales, etc. This feature depends on the listen gem.
# config.file_watcher = ActiveSupport::EventedFileUpdateChecker

System configuration

Rails version:
Rails 5.0.0
Ruby version:
ruby 2.3.0p0

[vipulnsward]

Can you create a sample application replicating this for debugging?

[amree]

Just want to chip in.

I'm probably having the same issue. I noticed my fsevent_watch can go up to more than 500 and I can't start new process after that. I can confirm it happens whenever I close my laptop without turning off rails server. So, when I opened my laptop and refresh the localhost, new fsevent_watch somehow will be started even though they already exists. Killing rails server will only kill the new fsevent_watch, not those from before I close my laptop. So, opening and closing the laptop will gradually increase fsevent_watch processes.

System Configuration

Rails version:
Rails 5.0.0.1
Ruby Version
2.3.1p112

[benaubin]

@vipulnsward Yes. In fact, there's a command to do so:

rails new thisbreaksmylaptop

[rvirani1]

All 3 devs on our team are having this issue as well.

[benaubin]

Ok, I came up with a workaround. Looks like it's not only the spring-watch-listen gem, and while removing it helps slightly (I think it might have just been a placebo), it doesn't fully solve the problem.

First I removed the listen and spring-watcher-listen gems.
Then, in my environments/development.rb file, I commented out this line:

 # Use an evented file watcher to asynchronously detect changes in source code,
 # routes, locales, etc. This feature depends on the listen gem.
 # config.file_watcher = ActiveSupport::EventedFileUpdateChecker

Then, Rails seems to work fine.

I very much recommend making using the listen gem opt-in, not opt-out, as it's very hard to debug. Also, laptop breaking probably turns many developers away from rails (it almost did for me).

The listen gem was added in #22254.

[benaubin]

I'm tagging @fnx, as it looks the listen implementation in Rails which he wrote is what contributes to this, not just the spring-watcher-listen gem.

[metacortex]

+1

Now I'm killing manually.
pkill -9 fsevent_wat*

[ahoward]

i'm seeing this too. it is way too easy to orphan processes. the listen gem is a piece of shit and should be removed.

[ahoward]

amateur hour: https://github.com/thibaudgg/rb-fsevent/blob/d803637/lib/rb-fsevent/fsevent.rb#L55