This class is capable of spawning instances of a single Ruby on Rails application. It does so by preloading as much of the application‘s code as possible, then creating instances of the application using what is already preloaded. This makes it spawning application instances very fast, except for the first spawn.

Use multiple instances of ApplicationSpawner if you need to spawn multiple different Ruby on Rails applications.

Note: ApplicationSpawner may only be started asynchronously with AbstractServer#start. Starting it synchronously with AbstractServer#start_synchronously has not been tested.

Methods
Included Modules
Classes and Modules
Class Passenger::Railz::ApplicationSpawner::Error
Constants
ROOT_UID = 0
  The user ID of the root user.
ROOT_GID = 0
  The group ID of the root user.
Attributes
[R] app_root The application root of this spawner.
[RW] time An attribute, used internally. This should not be used outside Passenger.
Public Class methods
new(app_root, lower_privilege = true, lowest_user = "nobody", environment = "production")

app_root is the root directory of this application, i.e. the directory that contains ‘app/’, ‘public/’, etc. If given an invalid directory, or a directory that doesn‘t appear to be a Rails application root directory, then an ArgumentError will be raised.

If lower_privilege is true, then ApplicationSpawner will attempt to switch to the user who owns the application‘s config/environment.rb, and to the default group of that user.

If that user doesn‘t exist on the system, or if that user is root, then ApplicationSpawner will attempt to switch to the username given by lowest_user (and to the default group of that user). If lowest_user doesn‘t exist either, or if switching user failed (because the current process does not have the privilege to do so), then ApplicationSpawner will continue without reporting an error.

The environment argument allows one to specify the RAILS_ENV environment to use.

    # File lib/passenger/railz/application_spawner.rb, line 78
78:         def initialize(app_root, lower_privilege = true, lowest_user = "nobody", environment = "production")
79:                 super()
80:                 begin
81:                         @app_root = normalize_path(app_root)
82:                 rescue SystemCallError => e
83:                         raise ArgumentError, e.message
84:                 rescue ArgumentError
85:                         raise
86:                 end
87:                 @lower_privilege = lower_privilege
88:                 @lowest_user = lowest_user
89:                 @environment = environment
90:                 self.time = Time.now
91:                 assert_valid_app_root(@app_root)
92:                 define_message_handler(:spawn_application, :handle_spawn_application)
93:         end
Public Instance methods
spawn_application()

Spawn an instance of the RoR application. When successful, an Application object will be returned, which represents the spawned RoR application.

Raises:

     # File lib/passenger/railz/application_spawner.rb, line 101
101:         def spawn_application
102:                 server.write("spawn_application")
103:                 pid, socket_name, using_abstract_namespace = server.read
104:                 if pid.nil?
105:                         raise IOError, "Connection closed"
106:                 end
107:                 owner_pipe = server.recv_io
108:                 return Application.new(@app_root, pid, socket_name,
109:                         using_abstract_namespace == "true", owner_pipe)
110:         rescue SystemCallError, IOError, SocketError => e
111:                 raise Error, "The application spawner server exited unexpectedly"
112:         end
spawn_application!()

Spawn an instance of the RoR application. When successful, an Application object will be returned, which represents the spawned RoR application.

Unlike spawn_application, this method may be called even when the ApplicationSpawner server isn‘t started. This allows one to spawn a RoR application without preloading any source files.

This method may only be called if no Rails framework has been loaded in the current Ruby VM.

Raises:

  • AppInitError: The Ruby on Rails application raised an exception or called exit() during startup.
  • SystemCallError, IOError, SocketError: Something went wrong.
     # File lib/passenger/railz/application_spawner.rb, line 128
128:         def spawn_application!
129:                 # Double fork to prevent zombie processes.
130:                 a, b = UNIXSocket.pair
131:                 pid = safe_fork(self.class.to_s) do
132:                         safe_fork('application') do
133:                                 begin
134:                                         a.close
135:                                         channel = MessageChannel.new(b)
136:                                         success = report_app_init_status(channel) do
137:                                                 ENV['RAILS_ENV'] = @environment
138:                                                 Dir.chdir(@app_root)
139:                                                 if @lower_privilege
140:                                                         lower_privilege('config/environment.rb', @lowest_user)
141:                                                 end
142:                                                 require 'config/environment'
143:                                                 require 'dispatcher'
144:                                         end
145:                                         if success
146:                                                 start_request_handler(channel)
147:                                         end
148:                                 rescue SignalException => e
149:                                         if e.message != AbstractRequestHandler::HARD_TERMINATION_SIGNAL &&
150:                                            e.message != AbstractRequestHandler::SOFT_TERMINATION_SIGNAL
151:                                                 raise
152:                                         end
153:                                 end
154:                         end
155:                 end
156:                 b.close
157:                 Process.waitpid(pid) rescue nil
158:                 
159:                 channel = MessageChannel.new(a)
160:                 unmarshal_and_raise_errors(channel)
161:                 
162:                 # No exception was raised, so spawning succeeded.
163:                 pid, socket_name, using_abstract_namespace = channel.read
164:                 if pid.nil?
165:                         raise IOError, "Connection closed"
166:                 end
167:                 owner_pipe = channel.recv_io
168:                 return Application.new(@app_root, pid, socket_name,
169:                         using_abstract_namespace == "true", owner_pipe)
170:         end
start()

Overrided from AbstractServer#start.

May raise these additional exceptions:

     # File lib/passenger/railz/application_spawner.rb, line 178
178:         def start
179:                 super
180:                 begin
181:                         unmarshal_and_raise_errors(server)
182:                 rescue IOError, SystemCallError, SocketError
183:                         stop
184:                         raise Error, "The application spawner server exited unexpectedly"
185:                 rescue
186:                         stop
187:                         raise
188:                 end
189:         end