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# -*- coding: utf-8 -*-
# daemon.py
# Copyright (C) 2013 LEAP
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
"""
A singleton daemon for running RPC services using protobuf.socketrpc.
"""
import logging
import threading
from protobuf.socketrpc.server import (
SocketRpcServer,
ThreadedTCPServer,
SocketHandler,
)
logger = logging.getLogger(__name__)
class ServiceAlreadyRunningException(Exception):
"""
Raised whenever a service is already running in this process but someone
attemped to start it in a different port.
"""
class EventsRpcServer(SocketRpcServer):
"""
RPC server used in server and component interfaces to receive messages.
"""
def __init__(self, port, host='localhost'):
"""
Initialize a RPC server.
:param port: the port in which to listen for incoming messages
:type port: int
:param host: the address to bind to
:type host: str
"""
SocketRpcServer.__init__(self, port, host)
self._server = None
def run(self):
"""
Run the server.
"""
logger.info('Running server on port %d.' % self.port)
# parent implementation does not hold the server instance, so we do it
# here.
self._server = ThreadedTCPServer((self.host, self.port),
SocketHandler, self)
# if we chose to use a random port, fetch the port number info.
if self.port is 0:
self.port = self._server.socket.getsockname()[1]
self._server.serve_forever()
def stop(self):
"""
Stop the server.
"""
self._server.shutdown()
class EventsSingletonDaemon(threading.Thread):
"""
Singleton class for for launching and terminating a daemon.
This class is used so every part of the mechanism that needs to listen for
messages can launch its own daemon (thread) to do the job.
"""
# Singleton instance
__instance = None
def __new__(cls, *args, **kwargs):
"""
Return a singleton instance if it exists or create and initialize one.
"""
if len(args) is not 2:
raise TypeError("__init__() takes exactly 2 arguments (%d given)"
% len(args))
if cls.__instance is None:
cls.__instance = object.__new__(
EventsSingletonDaemon)
cls.__initialize(cls.__instance, args[0], args[1])
return cls.__instance
@staticmethod
def __initialize(self, port, service):
"""
Initialize a singleton daemon.
This is a static method disguised as instance method that actually
does the initialization of the daemon instance.
:param port: the port in which to listen for incoming messages
:type port: int
:param service: the service to provide in this daemon
:type service: google.protobuf.service.Service
"""
threading.Thread.__init__(self)
self._port = port
self._service = service
self._server = EventsRpcServer(self._port)
self._server.registerService(self._service)
self.daemon = True
def __init__(self):
"""
Singleton placeholder initialization method.
Initialization is made in __new__ so we can always return the same
instance upon object creation.
"""
pass
@classmethod
def ensure(cls, port):
"""
Make sure the daemon instance is running.
Each implementation of this method should call `self.ensure_service`
with the appropriate service from the `events.proto` definitions, and
return the daemon instance.
:param port: the port in which the daemon should be listening
:type port: int
:return: a daemon instance
:rtype: EventsSingletonDaemon
"""
raise NotImplementedError(self.ensure)
@classmethod
def ensure_service(cls, port, service):
"""
Start the singleton instance if not already running.
Might return ServiceAlreadyRunningException
:param port: the port in which the daemon should be listening
:type port: int
:return: a daemon instance
:rtype: EventsSingletonDaemon
"""
daemon = cls(port, service)
if not daemon.is_alive():
daemon.start()
elif port and port != cls.__instance._port:
# service is running in this process but someone is trying to
# start it in another port
raise ServiceAlreadyRunningException(
"Service is already running in this process on port %d."
% self.__instance._port)
return daemon
@classmethod
def get_instance(cls):
"""
Retrieve singleton instance of this daemon.
:return: a daemon instance
:rtype: EventsSingletonDaemon
"""
return cls.__instance
def run(self):
"""
Run the server.
"""
self._server.run()
def stop(self):
"""
Stop the daemon.
"""
self._server.stop()
def get_port(self):
"""
Retrieve the value of the port to which the service running in this
daemon is binded to.
:return: the port to which the daemon is binded to
:rtype: int
"""
if self._port is 0:
self._port = self._server.port
return self._port
|
