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README.md

Spring

Spring is a Rails application preloader. It's trying to solve the same problem as spork, zeus and commands.

I made it because we are having a discussion on the rails core team about shipping something to solve this problem with rails. So this is my proposal, as working code.

(At least I hope it's working code, but this is alpha software at the moment. Please do try it and let me know if you hit problems.)

Features

Spring is most similar to Zeus, but it's implemented in pure Ruby, and is more tightly integrated with Rails (it makes use of Rails' built-in code reloader).

Spring tries to be totally automatic. It boots up in the background the first time you run a command. Then it speeds up subsequent commands. If it detects that your pre-loaded environment has changed (maybe config/application.rb has been edited) then it will reload your environment in the background, ready for the next command. When you close your terminal session, Spring will automatically shut down. There's no "server" to manually start and stop.

Spring operates via a command line interface. Other solutions (e.g. commands) take the approach of using a special console to run commands from. This means we will have to re-implement shell features such as history, completion, etc. Whilst it's not impossible to re-implement those features, it's unnecessary work and our re-implementation won't be as feature complete as a real shell. Using a real shell also prevents the user having to constantly jump between a terminal with a real shell and a terminal running the rails "commands console".

Compatibility

At the moment only MRI 1.9.3 / Rails 3.2 is supported.

Usage

Add spring to your gemfile and do a bundle.

You now have a spring command. Do a rbenv rehash if necessary. Note that on my machine I had over 700 gems installed, and activating the gem to run the spring command added over 0.5s to the runtime. Clearing out my gems solved the problem, but I'd like to figure out a way to speed this up.

For this walkthrough, I'm using the test app in the Spring repository:

cd /path/to/spring/test/apps/rails-3-2

We can run a test:

$ time spring test test/functional/posts_controller_test.rb
Run options:

# Running tests:

.......

Finished tests in 0.169882s, 41.2051 tests/s, 58.8644 assertions/s.

7 tests, 10 assertions, 0 failures, 0 errors, 0 skips

real    0m1.858s
user    0m0.184s
sys 0m0.067s

That booted our app in the background:

$ ps ax | grep spring
 8692 pts/6    Sl     0:00 /home/turnip/.rbenv/versions/1.9.3-p194/bin/ruby -r bundler/setup -r spring/server -e Spring::Server.boot
 8698 pts/6    Sl     0:02 /home/turnip/.rbenv/versions/1.9.3-p194/bin/ruby -r bundler/setup -r spring/server -e Spring::Server.boot

We can see two processes, one is the Spring server, the other is the application running in the test environment. When we close the terminal, the processes will be killed automatically.

Running the tests is faster next time:

$ time spring test test/functional/posts_controller_test.rb
Run options:

# Running tests:

.......

Finished tests in 0.162963s, 42.9546 tests/s, 61.3637 assertions/s.

7 tests, 10 assertions, 0 failures, 0 errors, 0 skips

real    0m0.492s
user    0m0.179s
sys 0m0.063s

If we edit any of the application files, or test files, the change will be picked up on the next run, without having the background process having to be restarted. This works even if you e.g. referenced your Post model in an initializer and then edited it.

If we edit any of the preloaded files, the application needs to restart automatically. Note that the application process id is 8698 above. Let's "edit" the config/application.rb:

$ touch config/application.rb
$ ps ax | grep spring
 8692 pts/6    Sl     0:00 /home/turnip/.rbenv/versions/1.9.3-p194/bin/ruby -r bundler/setup -r spring/server -e Spring::Server.boot
 8876 pts/6    Sl     0:00 /home/turnip/.rbenv/versions/1.9.3-p194/bin/ruby -r bundler/setup -r spring/server -e Spring::Server.boot

The application process detected the change and exited. The server process then detected that the application process exited, so it started a new application. All of this happens automatically in the background. Next time we run a command we'll be running against a fresh application.

If we run a command that uses a different environment, then it gets booted up. For example, the rake command uses the development environment by default:

$ time spring rake routes
    posts GET    /posts(.:format)          posts#index
          POST   /posts(.:format)          posts#create
 new_post GET    /posts/new(.:format)      posts#new
edit_post GET    /posts/:id/edit(.:format) posts#edit
     post GET    /posts/:id(.:format)      posts#show
          PUT    /posts/:id(.:format)      posts#update
          DELETE /posts/:id(.:format)      posts#destroy

real    0m0.763s
user    0m0.185s
sys 0m0.063s

We now have 3 processes: the server, and application in test mode and the application in development mode.

$ ps ax | grep spring
 8692 pts/6    Sl     0:00 /home/turnip/.rbenv/versions/1.9.3-p194/bin/ruby -r bundler/setup -r spring/server -e Spring::Server.boot
 8876 pts/6    Sl     0:15 /home/turnip/.rbenv/versions/1.9.3-p194/bin/ruby -r bundler/setup -r spring/server -e Spring::Server.boot
 9088 pts/6    Sl     0:01 /home/turnip/.rbenv/versions/1.9.3-p194/bin/ruby -r bundler/setup -r spring/server -e Spring::Server.boot

Running rake is faster the second time:

$ time spring rake routes
    posts GET    /posts(.:format)          posts#index
          POST   /posts(.:format)          posts#create
 new_post GET    /posts/new(.:format)      posts#new
edit_post GET    /posts/:id/edit(.:format) posts#edit
     post GET    /posts/:id(.:format)      posts#show
          PUT    /posts/:id(.:format)      posts#update
          DELETE /posts/:id(.:format)      posts#destroy

real    0m0.341s
user    0m0.177s
sys 0m0.070s

Commands

The following commands are shipped by default.

Custom commands can be specified in config/initializers/spring.rb. See lib/spring/commands.rb for examples.

test

Runs a test (e.g. Test::Unit, MiniTest::Unit, etc.) Preloads the test_helper file.

rspec

Runs an rspec spec, exactly the same as the rspec executable. Preloads the spec_helper file.

rake

Runs a rake task.

console

Boots into the Rails console. Currently this is usable but not perfect, for example you can't scroll back through command history. (That will be fixed.)

generate

Runs a Rails generator.

runner

The Rails runner.

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