Source code for pydispatch.dispatcher

"""Multiple-producer-multiple-consumer signal-dispatching

dispatcher is the core of the PyDispatcher system,
providing the primary API and the core logic for the

Module attributes of note:

    Any -- Singleton used to signal either "Any Sender" or
        "Any Signal".  See documentation of the _Any class.
    Anonymous -- Singleton used to signal "Anonymous Sender"
        See documentation of the _Anonymous class.

Internal attributes:
    WEAKREF_TYPES -- tuple of types/classes which represent
        weak references to receivers, and thus must be de-
        referenced on retrieval to retrieve the callable
    connections -- { senderkey (id) : { signal : [receivers...]}}
    senders -- { senderkey (id) : weakref(sender) }
        used for cleaning up sender references on sender
    sendersBack -- { receiverkey (id) : [senderkey (id)...] }
        used for cleaning up receiver references on receiver
        deletion, (considerably speeds up the cleanup process
        vs. the original code.)
from __future__ import generators
import weakref
from grass.pydispatch import saferef, robustapply, errors

__author__ = "Patrick K. O'Brien <>"
__cvsid__ = "Id:,v 1.1 2010/03/30 15:45:55 mcfletch Exp"
__version__ = "Revision: 1.1"

class _Parameter:
    """Used to represent default parameter values."""
    def __repr__(self):
        return self.__class__.__name__

class _Any(_Parameter):
    """Singleton used to signal either "Any Sender" or "Any Signal"

    The Any object can be used with connect, disconnect,
    send, or sendExact to signal that the parameter given
    Any should react to all senders/signals, not just
    a particular sender/signal.
Any = _Any()

class _Anonymous(_Parameter):
    """Singleton used to signal "Anonymous Sender"

    The Anonymous object is used to signal that the sender
    of a message is not specified (as distinct from being
    "any sender").  Registering callbacks for Anonymous
    will only receive messages sent without senders.  Sending
    with anonymous will only send messages to those receivers
    registered for Any or Anonymous.

        The default sender for connect is Any, while the
        default sender for send is Anonymous.  This has
        the effect that if you do not specify any senders
        in either function then all messages are routed
        as though there was a single sender (Anonymous)
        being used everywhere.
Anonymous = _Anonymous()

WEAKREF_TYPES = (weakref.ReferenceType, saferef.BoundMethodWeakref)

connections = {}
senders = {}
sendersBack = {}

[docs]def connect(receiver, signal=Any, sender=Any, weak=True): """Connect receiver to sender for signal receiver -- a callable Python object which is to receive messages/signals/events. Receivers must be hashable objects. if weak is True, then receiver must be weak-referencable (more precisely saferef.safeRef() must be able to create a reference to the receiver). Receivers are fairly flexible in their specification, as the machinery in the robustApply module takes care of most of the details regarding figuring out appropriate subsets of the sent arguments to apply to a given receiver. Note: if receiver is itself a weak reference (a callable), it will be de-referenced by the system's machinery, so *generally* weak references are not suitable as receivers, though some use might be found for the facility whereby a higher-level library passes in pre-weakrefed receiver references. signal -- the signal to which the receiver should respond if Any, receiver will receive any signal from the indicated sender (which might also be Any, but is not necessarily Any). Otherwise must be a hashable Python object other than None (DispatcherError raised on None). sender -- the sender to which the receiver should respond if Any, receiver will receive the indicated signals from any sender. if Anonymous, receiver will only receive indicated signals from send/sendExact which do not specify a sender, or specify Anonymous explicitly as the sender. Otherwise can be any python object. weak -- whether to use weak references to the receiver By default, the module will attempt to use weak references to the receiver objects. If this parameter is false, then strong references will be used. returns None, may raise DispatcherTypeError """ if signal is None: raise errors.DispatcherTypeError( 'Signal cannot be None (receiver=%r sender=%r)' % (receiver, sender) ) if weak: receiver = saferef.safeRef(receiver, onDelete=_removeReceiver) senderkey = id(sender) if senderkey in connections: signals = connections[senderkey] else: connections[senderkey] = signals = {} # Keep track of senders for cleanup. # Is Anonymous something we want to clean up? if sender not in (None, Anonymous, Any): def remove(object, senderkey=senderkey): _removeSender(senderkey=senderkey) # Skip objects that can not be weakly referenced, which means # they won't be automatically cleaned up, but that's too bad. try: weakSender = weakref.ref(sender, remove) senders[senderkey] = weakSender except: pass receiverID = id(receiver) # get current set, remove any current references to # this receiver in the set, including back-references if signal in signals: receivers = signals[signal] _removeOldBackRefs(senderkey, signal, receiver, receivers) else: receivers = signals[signal] = [] try: current = sendersBack.get(receiverID) if current is None: sendersBack[receiverID] = current = [] if senderkey not in current: current.append(senderkey) except: pass receivers.append(receiver)
[docs]def disconnect(receiver, signal=Any, sender=Any, weak=True): """Disconnect receiver from sender for signal receiver -- the registered receiver to disconnect signal -- the registered signal to disconnect sender -- the registered sender to disconnect weak -- the weakref state to disconnect disconnect reverses the process of connect, the semantics for the individual elements are logically equivalent to a tuple of (receiver, signal, sender, weak) used as a key to be deleted from the internal routing tables. (The actual process is slightly more complex but the semantics are basically the same). Note: Using disconnect is not required to cleanup routing when an object is deleted, the framework will remove routes for deleted objects automatically. It's only necessary to disconnect if you want to stop routing to a live object. returns None, may raise DispatcherTypeError or DispatcherKeyError """ if signal is None: raise errors.DispatcherTypeError( 'Signal cannot be None (receiver=%r sender=%r)' % (receiver, sender) ) if weak: receiver = saferef.safeRef(receiver) senderkey = id(sender) try: signals = connections[senderkey] receivers = signals[signal] except KeyError: raise errors.DispatcherKeyError( """No receivers found for signal %r from sender %r""" % ( signal, sender ) ) try: # also removes from receivers _removeOldBackRefs(senderkey, signal, receiver, receivers) except ValueError: raise errors.DispatcherKeyError( """No connection to receiver %s for signal %s from sender %s""" % ( receiver, signal, sender ) ) _cleanupConnections(senderkey, signal)
[docs]def getReceivers(sender=Any, signal=Any): """Get list of receivers from global tables This utility function allows you to retrieve the raw list of receivers from the connections table for the given sender and signal pair. Note: there is no guarantee that this is the actual list stored in the connections table, so the value should be treated as a simple iterable/truth value rather than, for instance a list to which you might append new records. Normally you would use liveReceivers(getReceivers(...)) to retrieve the actual receiver objects as an iterable object. """ try: return connections[id(sender)][signal] except KeyError: return []
[docs]def liveReceivers(receivers): """Filter sequence of receivers to get resolved, live receivers This is a generator which will iterate over the passed sequence, checking for weak references and resolving them, then returning all live receivers. """ for receiver in receivers: if isinstance(receiver, WEAKREF_TYPES): # Dereference the weak reference. receiver = receiver() if receiver is not None: yield receiver else: yield receiver
[docs]def getAllReceivers(sender=Any, signal=Any): """Get list of all receivers from global tables This gets all receivers which should receive the given signal from sender, each receiver should be produced only once by the resulting generator """ receivers = {} for set in ( # Get receivers that receive *this* signal from *this* sender. getReceivers(sender, signal), # Add receivers that receive *any* signal from *this* sender. getReceivers(sender, Any), # Add receivers that receive *this* signal from *any* sender. getReceivers(Any, signal), # Add receivers that receive *any* signal from *any* sender. getReceivers(Any, Any), ): for receiver in set: if receiver: # filter out dead instance-method weakrefs try: if receiver not in receivers: receivers[receiver] = 1 yield receiver except TypeError: # dead weakrefs raise TypeError on hash... pass
[docs]def send(signal=Any, sender=Anonymous, *arguments, **named): """Send signal from sender to all connected receivers. signal -- (hashable) signal value, see connect for details sender -- the sender of the signal if Any, only receivers registered for Any will receive the message. if Anonymous, only receivers registered to receive messages from Anonymous or Any will receive the message Otherwise can be any python object (normally one registered with a connect if you actually want something to occur). arguments -- positional arguments which will be passed to *all* receivers. Note that this may raise TypeErrors if the receivers do not allow the particular arguments. Note also that arguments are applied before named arguments, so they should be used with care. named -- named arguments which will be filtered according to the parameters of the receivers to only provide those acceptable to the receiver. Return a list of tuple pairs [(receiver, response), ... ] if any receiver raises an error, the error propagates back through send, terminating the dispatch loop, so it is quite possible to not have all receivers called if a raises an error. """ # Call each receiver with whatever arguments it can accept. # Return a list of tuple pairs [(receiver, response), ... ]. responses = [] for receiver in liveReceivers(getAllReceivers(sender, signal)): response = robustapply.robustApply( receiver, signal=signal, sender=sender, *arguments, **named ) responses.append((receiver, response)) return responses
[docs]def sendExact(signal=Any, sender=Anonymous, *arguments, **named): """Send signal only to those receivers registered for exact message sendExact allows for avoiding Any/Anonymous registered handlers, sending only to those receivers explicitly registered for a particular signal on a particular sender. """ responses = [] for receiver in liveReceivers(getReceivers(sender, signal)): response = robustapply.robustApply( receiver, signal=signal, sender=sender, *arguments, **named ) responses.append((receiver, response)) return responses
def _removeReceiver(receiver): """Remove receiver from connections.""" if not sendersBack or not connections: # During module cleanup the objects will be replaced with None # The order of replacing many change, so both variables need # to be checked. return False backKey = id(receiver) try: backSet = sendersBack.pop(backKey) except KeyError: return False else: for senderkey in backSet: try: signals = list(connections[senderkey]) except KeyError: pass else: for signal in signals: try: receivers = connections[senderkey][signal] except KeyError: pass else: try: receivers.remove(receiver) except Exception: pass _cleanupConnections(senderkey, signal) def _cleanupConnections(senderkey, signal): """Delete any empty signals for senderkey. Delete senderkey if empty.""" try: receivers = connections[senderkey][signal] except: pass else: if not receivers: # No more connected receivers. Therefore, remove the signal. try: signals = connections[senderkey] except KeyError: pass else: del signals[signal] if not signals: # No more signal connections. Therefore, remove the sender. _removeSender(senderkey) def _removeSender(senderkey): """Remove senderkey from connections.""" _removeBackrefs(senderkey) try: del connections[senderkey] except KeyError: pass # Senderkey will only be in senders dictionary if sender # could be weakly referenced. try: del senders[senderkey] except: pass def _removeBackrefs(senderkey): """Remove all back-references to this senderkey""" try: signals = connections[senderkey] except KeyError: signals = None else: items = signals.items() def allReceivers(): for signal, set in items: for item in set: yield item for receiver in allReceivers(): _killBackref(receiver, senderkey) def _removeOldBackRefs(senderkey, signal, receiver, receivers): """Kill old sendersBack references from receiver This guards against multiple registration of the same receiver for a given signal and sender leaking memory as old back reference records build up. Also removes old receiver instance from receivers """ try: index = receivers.index(receiver) # need to scan back references here and remove senderkey except ValueError: return False else: oldReceiver = receivers[index] del receivers[index] found = 0 signals = connections.get(signal) if signals is not None: for sig, recs in connections.get(signal, {}).iteritems(): if sig != signal: for rec in recs: if rec is oldReceiver: found = 1 break if not found: _killBackref(oldReceiver, senderkey) return True return False def _killBackref(receiver, senderkey): """Do the actual removal of back reference from receiver to senderkey""" receiverkey = id(receiver) set = sendersBack.get(receiverkey, ()) while senderkey in set: try: set.remove(senderkey) except: break if not set: try: del sendersBack[receiverkey] except KeyError: pass return True