An abstract base class for a server, with the following properties:

  • The server has exactly one client, and is connected to that client at all times. The server will quit when the connection closes.
  • The server‘s main loop may be run in a child process (and so is asynchronous from the main process).
  • One can communicate with the server through discrete messages (as opposed to byte streams).
  • The server can pass file descriptors (IO objects) back to the client.

A message is just an ordered list of strings. The first element in the message is the _message name_.

The server will also reset all signal handlers (in the child process). That is, it will respond to all signals in the default manner. The only exception is SIGHUP, which is ignored. One may define additional signal handlers using define_signal_handler().

Before an AbstractServer can be used, it must first be started by calling start(). When it is no longer needed, stop() should be called.

Here‘s an example on using AbstractServer:

 class MyServer < PhusionPassenger::AbstractServer
    def initialize
       super()
       define_message_handler(:hello, :handle_hello)
    end

    def hello(first_name, last_name)
       send_to_server('hello', first_name, last_name)
       reply, pointless_number = recv_from_server
       puts "The server said: #{reply}"
       puts "In addition, it sent this pointless number: #{pointless_number}"
    end

 private
    def handle_hello(first_name, last_name)
       send_to_client("Hello #{first_name} #{last_name}, how are you?", 1234)
    end
 end

 server = MyServer.new
 server.start
 server.hello("Joe", "Dalton")
 server.stop
Methods
Included Modules
Classes and Modules
Class PhusionPassenger::AbstractServer::ServerAlreadyStarted
Class PhusionPassenger::AbstractServer::ServerError
Class PhusionPassenger::AbstractServer::ServerNotStarted
Class PhusionPassenger::AbstractServer::UnknownMessage
Constants
SERVER_TERMINATION_SIGNAL = "SIGTERM"
Attributes
[RW] last_activity_time The last time when this AbstractServer had processed a message.
[RW] max_idle_time The maximum time that this AbstractServer may be idle. Used by AbstractServerCollection to determine when this object should be cleaned up. nil or 0 indicate that this object should never be idle cleaned.
[RW] next_cleaning_time Used by AbstractServerCollection to remember when this AbstractServer should be idle cleaned.
Public Class methods
new()
     # File lib/phusion_passenger/abstract_server.rb, line 109
109:         def initialize
110:                 @done = false
111:                 @message_handlers = {}
112:                 @signal_handlers = {}
113:                 @orig_signal_handlers = {}
114:                 @last_activity_time = Time.now
115:         end
Public Instance methods
server_pid()

Return the PID of the started server. This is only valid if start() has been called.

     # File lib/phusion_passenger/abstract_server.rb, line 244
244:         def server_pid
245:                 return @pid
246:         end
start()

Start the server. This method does not block since the server runs asynchronously from the current process.

You may only call this method if the server is not already started. Otherwise, a ServerAlreadyStarted will be raised.

Derived classes may raise additional exceptions.

     # File lib/phusion_passenger/abstract_server.rb, line 124
124:         def start
125:                 if started?
126:                         raise ServerAlreadyStarted, "Server is already started"
127:                 end
128:                 
129:                 @parent_socket, @child_socket = UNIXSocket.pair
130:                 before_fork
131:                 @pid = fork
132:                 if @pid.nil?
133:                         begin
134:                                 STDOUT.sync = true
135:                                 STDERR.sync = true
136:                                 @parent_socket.close
137:                                 
138:                                 # During Passenger's early days, we used to close file descriptors based
139:                                 # on a white list of file descriptors. That proved to be way too fragile:
140:                                 # too many file descriptors are being left open even though they shouldn't
141:                                 # be. So now we close file descriptors based on a black list.
142:                                 #
143:                                 # Note that STDIN, STDOUT and STDERR may be temporarily set to
144:                                 # different file descriptors than 0, 1 and 2, e.g. in unit tests.
145:                                 # We don't want to close these either.
146:                                 file_descriptors_to_leave_open = [0, 1, 2, @child_socket.fileno,
147:                                         fileno_of(STDIN), fileno_of(STDOUT), fileno_of(STDERR)].compact.uniq
148:                                 NativeSupport.close_all_file_descriptors(file_descriptors_to_leave_open)
149:                                 # In addition to closing the file descriptors, one must also close
150:                                 # the associated IO objects. This is to prevent IO.close from
151:                                 # double-closing already closed file descriptors.
152:                                 close_all_io_objects_for_fds(file_descriptors_to_leave_open)
153:                                 
154:                                 # At this point, RubyGems might have open file handles for which
155:                                 # the associated file descriptors have just been closed. This can
156:                                 # result in mysterious 'EBADFD' errors. So we force RubyGems to
157:                                 # clear all open file handles.
158:                                 Gem.clear_paths
159:                                 
160:                                 # Reseed pseudo-random number generator for security reasons.
161:                                 srand
162:                                 
163:                                 start_synchronously(@child_socket)
164:                         rescue Interrupt
165:                                 # Do nothing.
166:                         rescue SignalException => signal
167:                                 if signal.message == SERVER_TERMINATION_SIGNAL
168:                                         # Do nothing.
169:                                 else
170:                                         print_exception(self.class.to_s, signal)
171:                                 end
172:                         rescue Exception => e
173:                                 print_exception(self.class.to_s, e)
174:                         ensure
175:                                 exit!
176:                         end
177:                 end
178:                 @child_socket.close
179:                 @parent_channel = MessageChannel.new(@parent_socket)
180:         end
start_synchronously(socket)

Start the server, but in the current process instead of in a child process. This method blocks until the server‘s main loop has ended.

socket is the socket that the server should listen on. The server main loop will end if the socket has been closed.

All hooks will be called, except before_fork().

     # File lib/phusion_passenger/abstract_server.rb, line 189
189:         def start_synchronously(socket)
190:                 @child_socket = socket
191:                 @child_channel = MessageChannel.new(socket)
192:                 begin
193:                         reset_signal_handlers
194:                         initialize_server
195:                         begin
196:                                 main_loop
197:                         ensure
198:                                 finalize_server
199:                         end
200:                 ensure
201:                         revert_signal_handlers
202:                 end
203:         end
started?()

Return whether the server has been started.

     # File lib/phusion_passenger/abstract_server.rb, line 239
239:         def started?
240:                 return !@parent_channel.nil?
241:         end
stop()

Stop the server. The server will quit as soon as possible. This method waits until the server has been stopped.

When calling this method, the server must already be started. If not, a ServerNotStarted will be raised.

     # File lib/phusion_passenger/abstract_server.rb, line 210
210:         def stop
211:                 if !started?
212:                         raise ServerNotStarted, "Server is not started"
213:                 end
214:                 
215:                 @parent_socket.close
216:                 @parent_channel = nil
217:                 
218:                 # Wait at most 3 seconds for server to exit. If it doesn't do that,
219:                 # we kill it. If that doesn't work either, we kill it forcefully with
220:                 # SIGKILL.
221:                 begin
222:                         Timeout::timeout(3) do
223:                                 Process.waitpid(@pid) rescue nil
224:                         end
225:                 rescue Timeout::Error
226:                         Process.kill(SERVER_TERMINATION_SIGNAL, @pid) rescue nil
227:                         begin
228:                                 Timeout::timeout(3) do
229:                                         Process.waitpid(@pid) rescue nil
230:                                 end
231:                         rescue Timeout::Error
232:                                 Process.kill('SIGKILL', @pid) rescue nil
233:                                 Process.waitpid(@pid, Process::WNOHANG) rescue nil
234:                         end
235:                 end
236:         end
Protected Instance methods
before_fork()

A hook which is called when the server is being started, just before forking a new process. The default implementation does nothing, this method is supposed to be overrided by child classes.

     # File lib/phusion_passenger/abstract_server.rb, line 251
251:         def before_fork
252:         end
client()

Return the communication channel with the client (i.e. the parent process that started the server). This is a MessageChannel object.

     # File lib/phusion_passenger/abstract_server.rb, line 296
296:         def client
297:                 return @child_channel
298:         end
define_message_handler(message_name, handler)

Define a handler for a message. message_name is the name of the message to handle, and handler is the name of a method to be called (this may either be a String or a Symbol).

A message is just a list of strings, and so handler will be called with the message as its arguments, excluding the first element. See also the example in the class description.

     # File lib/phusion_passenger/abstract_server.rb, line 271
271:         def define_message_handler(message_name, handler)
272:                 @message_handlers[message_name.to_s] = handler
273:         end
define_signal_handler(signal, handler)

Define a handler for a signal.

     # File lib/phusion_passenger/abstract_server.rb, line 276
276:         def define_signal_handler(signal, handler)
277:                 @signal_handlers[signal.to_s] = handler
278:         end
fileno_of(io)
     # File lib/phusion_passenger/abstract_server.rb, line 305
305:         def fileno_of(io)
306:                 return io.fileno
307:         rescue
308:                 return nil
309:         end
finalize_server()

A hook which is called when the server is being stopped. This is called in the child process, after the main loop has been left. The default implementation does nothing, this method is supposed to be overrided by child classes.

     # File lib/phusion_passenger/abstract_server.rb, line 263
263:         def finalize_server
264:         end
initialize_server()

A hook which is called when the server is being started. This is called in the child process, before the main loop is entered. The default implementation does nothing, this method is supposed to be overrided by child classes.

     # File lib/phusion_passenger/abstract_server.rb, line 257
257:         def initialize_server
258:         end
quit_main()

Tell the main loop to stop as soon as possible.

     # File lib/phusion_passenger/abstract_server.rb, line 301
301:         def quit_main
302:                 @done = true
303:         end
server()

Return the communication channel with the server. This is a MessageChannel object.

Raises ServerNotStarted if the server hasn‘t been started yet.

This method may only be called in the parent process, and not in the started server process.

     # File lib/phusion_passenger/abstract_server.rb, line 287
287:         def server
288:                 if !started?
289:                         raise ServerNotStarted, "Server hasn't been started yet. Please call start() first."
290:                 end
291:                 return @parent_channel
292:         end