Source code for camelot.view.remote_signals

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"""
Classes to connect the QT event loop with a messaging
server.  To enable multiple clients to push model updates
to each other or messages for the users.

As a messaging server, Apache active MQ was tested in combination
with the stomp library (http://docs.codehaus.org/display/STOMP/Python)
"""

import logging
import re

LOGGER = logging.getLogger('remote_signals')

from PyQt4 import QtCore

#from camelot.core.threading import synchronized
from camelot.core.conf import settings

[docs]class SignalHandler(QtCore.QObject): """The signal handler connects multiple collection proxy classes to inform each other when they have changed an object. If the object is persistent (eg mapped by SQLAlchemy), the signal hanler can inform other signal handlers on the network of the change. A couple of the methods of this thread are protected by a QMutex through the synchronized decorator. It appears that python/qt deadlocks when the entity_update_signal is connected to and emitted at the same time. This can happen when the user closes a window that is still building up (the CollectionProxies are being constructed and they connect to the signal handler). These deadlock issues are resolved in recent PyQt, so comment out the mutex stuff. (2011-08-12) """ entity_update_signal = QtCore.pyqtSignal(object, object) entity_delete_signal = QtCore.pyqtSignal(object, object) entity_create_signal = QtCore.pyqtSignal(object, object) entity_update_pattern = r'^/topic/Camelot.Entity.(?P<entity>.*).update$' def __init__(self): super(SignalHandler, self).__init__() #self._mutex = QtCore.QMutex() self.update_expression = re.compile(self.entity_update_pattern) if hasattr(settings, 'CAMELOT_SERVER') and settings.CAMELOT_SERVER: from stomp import stomp self.connection = stomp.Connection(host_and_ports = [ (settings.CAMELOT_SERVER, 61613) ]) self.connection.add_listener( self ) self.connection.start() LOGGER.debug('connection to servers started') else: self.connection = None LOGGER.debug('not connected to a server') #@synchronized
[docs] def connect_signals(self, obj): """Connect the SignalHandlers its signals to the slots of obj, while the mutex is locked""" self.entity_update_signal.connect( obj.handle_entity_update, QtCore.Qt.QueuedConnection ) self.entity_delete_signal.connect( obj.handle_entity_delete, QtCore.Qt.QueuedConnection ) self.entity_create_signal.connect( obj.handle_entity_create, QtCore.Qt.QueuedConnection )
[docs] def on_error(self, headers, message): """Callback function for stomp to receive errors""" LOGGER.error('received an error %s'%message)
[docs] def on_message(self, headers, message): """Callback function for stomp to receive messages""" from elixir import entities LOGGER.debug('received a message %s : %s'%(str(headers), message)) match = self.update_expression.match(headers['destination']) if match: entity = match.group('entity') LOGGER.debug(' decoded as update signal for entity %s'%entity) self.entity_update_signal.emit( self, [e for e in entities if e.__name__==entity][0].get(eval(message)) )
[docs] def on_connecting(self, server): """Callback message for stomp to inform it is connecting to a messaging queue""" LOGGER.debug('try to connect to message service') self.connection.connect()
[docs] def on_connected(self, *args, **kwargs): """Callback message for stomp to inform it is connected to a messaging queue, this method will subscribe to the camelot topic""" LOGGER.debug('connected to message service %s, %s'%((str(args), str(kwargs)))) self.connection.subscribe(destination='/topic/Camelot.Entity.>', ack='auto')
[docs] def on_disconnected(self): """Callback message for stomp to inform it is disconnected from the messaging queue""" LOGGER.debug('stomp service disconnected')
[docs] def send_entity_update(self, sender, entity, scope='local'): """Call this method to inform the whole application an entity has changed""" self.sendEntityUpdate(sender, entity, scope) #@synchronized
[docs] def sendEntityUpdate(self, sender, entity, scope='local'): """Call this method to inform the whole application an entity has changed""" # deprecated self.entity_update_signal.emit( sender, entity ) if self.connection and scope == 'remote': self.connection.send(str([entity.id]), destination='/topic/Camelot.Entity.%s.update'%entity.__class__.__name__) #@synchronized
[docs] def sendEntityDelete(self, sender, entity, scope='local'): """Call this method to inform the whole application an entity is about to be deleted""" self.entity_delete_signal.emit( sender, entity ) if self.connection and scope == 'remote': self.connection.send(str([entity.id]), destination='/topic/Camelot.Entity.%s.delete'%entity.__class__.__name__) #@synchronized
[docs] def sendEntityCreate(self, sender, entity, scope='local'): """Call this method to inform the whole application an entity was created""" self.entity_create_signal.emit( sender, entity ) if self.connection and scope == 'remote': self.connection.send(str([entity.id]), destination='/topic/Camelot.Entity.%s.create'%entity.__class__.__name__)
_signal_handler_ = []
[docs]def construct_signal_handler(*args, **kwargs): """Construct the singleton signal handler""" _signal_handler_.append(SignalHandler(*args, **kwargs))
[docs]def get_signal_handler(): """Get the singleton signal handler""" if not len(_signal_handler_): construct_signal_handler() return _signal_handler_[-1]
[docs]def has_signal_handler(): """Request if the singleton signal handler was constructed""" return len(_signal_handler_)

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