Cross-thread violation on rb_gc()

Question

The codebase I'm working on was recently upgraded from Ruby 1.9.2 to Ruby 1.9.3 and from Rails 3.1 to Rails 3.2.2. Since I'm using RVM I simply did rvm install 1.9.3 which I would have expected to be all that was necessary.

When I run

rails s

I get the error

[BUG] cross-thread violation on rb_gc()

I've found a number of links relating to this problem. There is one on StackOverflow, but it doesn't really give an answer. The most promising answer is on the RVM site:

In every case of this I have seen thus far it has always ended up being that a ruby gem/library with C extensions was compiled against a different ruby and/or architecture than the one that is trying to load it. Try uninstalling & reinstalling gems with C extensions that your application uses to hunt this buggar down.

That's fairly helpful, but my Ruby-fu is not strong enough to know which gems have C extensions and which ones I should try to re-install. Quite a few of the other links on the topic seem to suggest that the json gem is at fault, so I tried following the suggested solution.

gem uninstall json 
gem install --platform=ruby

This didn't really change anything for me—I still get the exact same error when trying to start the Rails environment.

How do I track down this problem?

If it helps, here is the output from gem list:

actionmailer (3.2.2)
actionpack (3.2.2)
activemodel (3.2.2)
activerecord (3.2.2)
activeresource (3.2.2)
activesupport (3.2.2)
addressable (2.2.7)
akami (1.0.0)
arel (3.0.2)
bcrypt-ruby (3.0.1)
bson (1.6.1)
bson_ext (1.6.1)
builder (3.0.0)
bundler (1.1.3, 1.0.21)
capybara (1.1.2)
carmen (0.2.13)
childprocess (0.3.1)
ci_reporter (1.7.0)
coderay (1.0.5)
coffee-rails (3.2.2)
coffee-script (2.2.0)
coffee-script-source (1.2.0)
commonjs (0.2.5)
cucumber (1.1.9)
cucumber-rails (1.3.0)
database_cleaner (0.7.2)
devise (2.0.4)
diff-lcs (1.1.3)
ejs (1.0.0)
email_spec (1.2.1)
engineyard (1.4.28)
engineyard-serverside-adapter (1.6.3)
erubis (2.7.0)
escape (0.0.4)
execjs (1.3.0)
factory_girl (3.0.0)
factory_girl_rails (3.0.0)
faker (1.0.1)
fakeweb (1.3.0)
ffi (1.0.11)
gherkin (2.9.3)
gyoku (0.4.4)
haml (3.1.4)
haml-rails (0.3.4)
hash-deep-merge (0.1.1)
highline (1.6.11)
hike (1.2.1)
httpi (0.9.6)
i18n (0.6.0)
jasmine (1.1.2)
jasmine-core (1.1.0)
jasminerice (0.0.8)
journey (1.0.3)
jquery-rails (2.0.1)
json (1.6.6)
json_pure (1.6.6)
kaminari (0.13.0)
kgio (2.7.4)
launchy (2.0.5)
less (2.1.0)
less-rails (2.2.0)
libv8 (3.3.10.4 x86_64-darwin-11)
log4r (1.1.10)
mail (2.4.4)
metaclass (0.0.1)
method_source (0.7.1)
mime-types (1.18)
mocha (0.10.5)
mongo (1.6.1)
mongoid (2.4.7)
mongoid-rspec (1.4.4)
multi_json (1.2.0)
net-ssh (2.2.2)
newrelic_rpm (3.3.3)
nokogiri (1.5.2)
nori (1.1.0)
open4 (1.3.0)
orm_adapter (0.0.7)
polyglot (0.3.3)
pr_geohash (1.0.0)
pry (0.9.8.4)
pry-highlight (0.0.1)
pry_debug (0.0.1)
rack (1.4.1)
rack-cache (1.2)
rack-ssl (1.3.2)
rack-test (0.6.1)
rails (3.2.2)
rails-footnotes (3.7.6)
railties (3.2.2)
raindrops (0.8.0)
rake (0.9.2.2)
rdoc (3.12)
recursive-open-struct (0.2.1)
rest-client (1.6.7)
rpm_contrib (2.1.8)
rsolr (1.0.7)
rspec (2.9.0)
rspec-core (2.9.0)
rspec-expectations (2.9.0)
rspec-mocks (2.9.0)
rspec-rails (2.9.0)
rubyzip (0.9.6.1)
sass (3.1.15)
sass-rails (3.2.5)
savon (0.9.9)
selenium-webdriver (2.20.0)
settings-tree (0.2.1)
simplecov (0.6.1)
simplecov-html (0.5.3)
simplecov-rcov (0.2.3)
slop (2.4.4)
spine-rails (0.1.0)
spork (1.0.0rc2)
sprockets (2.1.2)
sunspot (1.3.1)
sunspot_mongoid (0.4.1)
sunspot_rails (1.3.1)
sunspot_solr (1.3.1)
term-ansicolor (1.0.7)
therubyracer (0.10.1)
thor (0.14.6)
tilt (1.3.3)
treetop (1.4.10)
twitter-bootstrap-rails (2.0.6)
tzinfo (0.3.32)
uglifier (1.2.4)
unicorn (4.2.1)
warden (1.1.1)
wasabi (2.1.0)
xpath (0.1.4)

Answer 1

Here are various approaches you can try.

cleanup

To clean up old versions of your gems:

gem cleanup --dryrun

json

To temporarily see if the json gem is the issue, switch from json (native) to json (pure ruby) and change your Gemfile:

gem install json_pure 

native gems

Your gem list has a few that pop out for me as native:

• bcrypt
• bson
• erubis
• ffi (enables lots of native connections)
• gherkin
• kgio
• less
• nokogiri
• raindrops
• therubyracer (many unpredictable issues IMHO)
• unicorn

ffi

Your gem ffi is especially interesting -- do you happen to know what you're doing with it?

The ffi enables Ruby code to call native code, for example if some part of your Ruby app needs to connect to native libraries.

When you're diagnosing your issue, I'd look at this gem first.

makefiles

To find any of your gems that have Makefile files, which is a good indicator that they have native code:

find / | grep "/ruby/gems/" | grep Makefile

To find all your gems so you can delete them:

find / | grep "/ruby/gems/"

nuke RVM

To nuke RVM or its pieces, you can use rvm uninstall, rvm implode, or this script which nukes RVM and finds any lingering pieces:

https://raw.github.com/SixArm/sixarm_unix_shell_scripts/master/rvm-uninstall-danger

try rbenv + bundler

I changed from using rvm to using rbenv + bundler and it's working great for me.

The rbenv tool is a direct competitor to rvm for managing Ruby versions: https://github.com/sstephenson/rbenv

Bundler is a great way to manage gemsets and gem dependencies: http://gembundler.com/

brew

If you're on a Mac and using MacPorts, to change to Homebrew:

Link

Answer 2

1. Uninstall all verions of json gems by running: gem uninstall json

2. Then run: gem install json --platform=ruby

3. Run bundle again:bundle install

Answer 3

You should try nuking all of your gems and reinstall them for your app using the bundle command.

Quoting the RVM documentation for this error:

Try uninstalling & reinstalling gems with C extensions that your application uses to hunt this buggar down.

The command to remove gems with RVM is simply:

rvm uninstall