ConnectionPool#with_connection fails to check connections back in

[chris-maginatics]

It's easy to repro:

irb(main):005:0> 20.times.map { Thread.new { Foo.connection_pool.with_connection { Foo.count } }.value }
ActiveRecord::ConnectionTimeoutError: could not obtain a database connection within 5.000 seconds (waited 5.000 seconds)

[rafaelfranca]

cc @matthewd @tenderlove

[chris-maginatics]

This may be a conflict with db_charmer. Investigating.

[matthewd]

@chris-maginatics any news?

[robin850]

(May be related with #12867 ; it looks like people are still experiencing such issue. However, this stacktrace does not include occurrences of db_charmer)

[chris-maginatics]

@matthewd We can repro with this Dockerfile:

FROM ubuntu:12.04
RUN apt-get update \
 && apt-get -y install ruby1.9.1 ruby1.9.1-dev libsqlite3-dev libmysqlclient-dev make g++ git-core \
 && gem install --no-rdoc --no-ri rails -v 4.0.3 \
 && gem install --no-rdoc --no-ri therubyracer \
 && rails new foo

WORKDIR /foo
RUN echo "source 'http://rubygems.org'" > Gemfile \
 && echo "gem 'rails', '4.0.3'" >>Gemfile \
 && echo "gem 'sqlite3'" >>Gemfile \
 && echo "gem 'therubyracer'" >>Gemfile \
 && rails generate model bar \
 && rake db:migrate

# This one succeeds
RUN bundle --quiet \
 && echo '20.times.map { Thread.new { Bar.connection_pool.with_connection { Bar.count } }.value }' | bundle exec rails c

# This one fails
RUN echo "gem 'db-charmer', :git => 'https://github.com/kovyrin/db-charmer.git', :ref => '886898af'" >>Gemfile \
 && bundle --quiet \
 && echo '20.times.map { Thread.new { Bar.connection_pool.with_connection { Bar.count } }.value }' | bundle exec rails c

So it's definitely an interaction with db-charmer. We haven't dug farther into it yet since we have a workaround (use ActiveRecord::Base.connection_pool.with_connection instead of Bar.connection_pool.with_connection).

[matthewd]

Okay, thanks. I'll declare this a db_charmer issue and close for now; please do yell if you find evidence to the contrary.