Ruby on rails 项目启动流程

众所周知，我们可以通过rails s 这个命令来启动一个rails 项目，但是这条命令都干了哪些事呢？抽时间研究了下，同时感谢tomwang1013的博客。当我们输入rails s 这个命令的时候，项目会加载项目bin/rails.rb 这个文件 
#!/usr/bin/env ruby 
APP_PATH = File.expand_path('../../config/application', __FILE__) 
require_relative '../config/boot' 
require 'rails/commands' 
通过代码我们可以看到这个文件中定义了一个APP_PATH 即我们的项目文件：config/application.rb，并require了config/boot，boot文件主要是做了bundle的初始化。 
然后，我们可以看到这个时候rails/commands（railties-3.2.3/lib/rails/commands.rb）文件被load进来，由于我们传入的command参数为s，也就是server，然后我们看看commands的这个文件的源码对应的部分：

when 'server' # Change to the application's path if there is no config.ru file in current dir. # This allows us to run script/rails server from other directories, but still get # the main config.ru and properly set the tmp directory. Dir.chdir(File.expand_path('../../', APP_PATH)) unless File.exists?(File.expand_path("config.ru")) require 'rails/commands/server' Rails::Server.new.tap { |server| # We need to require application after the server sets environment, # otherwise the --environment option given to the server won't propagate. require APP_PATH Dir.chdir(Rails.application.root) server.start } 

在server 这个方法中我们通过server.start这行代码可以看出最终调用了start这个方法，然后查看下start 这个方法。同时这里面也打印了我们熟悉的控制台信息

def start url = "#{options[:SSLEnable] ? 'https' : 'http'}://#{options[:Host]}:#{options[:Port]}" puts "=> Booting #{ActiveSupport::Inflector.demodulize(server)}" puts "=> Rails #{Rails.version} application starting in #{Rails.env} on #{url}" puts "=> Call with -d to detach" unless options[:daemonize] trap(:INT) { exit } puts "=> Ctrl-C to shutdown server" unless options[:daemonize] #Create required tmp directories if not found %w(cache pids sessions sockets).each do |dir_to_make| FileUtils.mkdir_p(Rails.root.join('tmp', dir_to_make)) end puts 'server start ---' super ensure # The '-h' option calls exit before @options is set. # If we call 'options' with it unset, we get double help banners. puts 'Exiting' unless @options && options[:daemonize] end 

这个start 这个方法最终会执行super 这个，super 会调用Rack::Server#start方法：代码

def start &blk if options[:warn] $-w = true end if includes = options[:include] $LOAD_PATH.unshift(*includes) end if library = options[:require] require library end if options[:debug] $DEBUG = true require 'pp' p options[:server] pp wrapped_app pp app end # Touch the wrapped app, so that the config.ru is loaded before # daemonization (i.e. before chdir, etc). wrapped_app daemonize_app if options[:daemonize] write_pid if options[:pid] trap(:INT) do if server.respond_to?(:shutdown) server.shutdown else exit end end server.run wrapped_app, options, &blk end 

代码执行到server.run wrapped_app 这行代码。wrapped_app方法最终又会调用Rack::Server#app

def app @app ||= begin if !::File.exist? options[:config] abort "configuration #{options[:config]} not found" end app, options = Rack::Builder.parse_file(self.options[:config], opt_parser) self.options.merge! options app end end 

最终app 这个方法会加载项目config 目录下的environment.rb这个文件如：

# Load the Rails application. require File.expand_path('../application', __FILE__) require 'whenever' module ProductConfig DYNAMIC_FIELDS = Hash.new end module RestConfig PRODUCT_SERVER = ENV["PHOTO_HOST"] || 'http://localhost:3001/' #CUSTOMER_SERVER = ENV["CUSTOMER_HOST"] || 'http://localhost:3001/' CUSTOMER_SERVER = ENV["CUSTOMER_HOST"] || 'http://localhost:3001/' OA_SERVER = 'http://localhost:3001/' #ELEPHANT_HOST = ENV["ELEPHANT_HOST"] || 'http://www.jiuyunda.net:90/' ELEPHANT_HOST = ENV["ELEPHANT_HOST"] || 'http://localhost:3001/' JXC_HOST = ENV["JXC_HOST"] || 'http://localhost:3001/' SETTLE_HOST = ENV["SETTLE_HOST"] || 'http://localhost:3001/' end # Initialize the Rails application. Rails.application.initialize!

Rails.application.initialize!这行代码我们可以看出 
项目的初始化完成。这个时候我们代码就回到Rack::Server#start方法的最后一行 server.run wrapped_app, options, &blk 由于我们没有设定任何参数。通过代码

def server @_server ||= Rack::Handler.get(options[:server]) || Rack::Handler.default(options) end def self.default(options = {}) # Guess. if ENV.include?("PHP_FCGI_CHILDREN") # We already speak FastCGI options.delete :File options.delete :Port Rack::Handler::FastCGI elsif ENV.include?("REQUEST_METHOD") Rack::Handler::CGI else begin Rack::Handler::Thin rescue LoadError Rack::Handler::WEBrick end end end 

我们可以看到rack 为我们选定了默认的server.一般来说是WEBrick .然后WEBrick启动，打印如下信息

INFO  WEBrick 1.3.1 INFO ruby 1.9.3 INFO WEBrick::HTTPServer#start: pid=28371 port=3000 

如果安装了其他application server的话打印的信息可能会不同如

Booting Puma
=> Rails 4.2.4 application starting in development on http://localhost:3000 => Run `rails server -h` for more startup options => Ctrl-C to shutdown server "assets end:false" Puma starting in single mode... * Version 3.4.0 (ruby 2.3.0-p0), codename: Owl Bowl Brawl * Min threads: 0, max threads: 16 * Environment: development * Listening on tcp://localhost:3000

至此项目的启动已完成。