import weakref import threading from django.dispatch import saferef WEAKREF_TYPES = (weakref.ReferenceType, saferef.BoundMethodWeakref) def _make_id(target): if hasattr(target, '__func__'): return (id(target.__self__), id(target.__func__)) return id(target) class Signal(object): """ Base class for all signals Internal attributes: receivers { receriverkey (id) : weakref(receiver) } """ def __init__(self, providing_args=None): """ Create a new signal. providing_args A list of the arguments this signal can pass along in a send() call. """ self.receivers = [] if providing_args is None: providing_args = [] self.providing_args = set(providing_args) self.lock = threading.Lock() def connect(self, receiver, sender=None, weak=True, dispatch_uid=None): """ Connect receiver to sender for signal. Arguments: receiver A function or an instance method which is to receive signals. 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 must be able to accept keyword arguments. If receivers have a dispatch_uid attribute, the receiver will not be added if another receiver already exists with that dispatch_uid. sender The sender to which the receiver should respond. Must either be of type Signal, or None to receive events from any sender. 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. dispatch_uid An identifier used to uniquely identify a particular instance of a receiver. This will usually be a string, though it may be anything hashable. """ from django.conf import settings # If DEBUG is on, check that we got a good receiver if settings.DEBUG: import inspect assert callable(receiver), "Signal receivers must be callable." # Check for **kwargs # Not all callables are inspectable with getargspec, so we'll # try a couple different ways but in the end fall back on assuming # it is -- we don't want to prevent registration of valid but weird # callables. try: argspec = inspect.getargspec(receiver) except TypeError: try: argspec = inspect.getargspec(receiver.__call__) except (TypeError, AttributeError): argspec = None if argspec: assert argspec[2] is not None, \ "Signal receivers must accept keyword arguments (**kwargs)." if dispatch_uid: lookup_key = (dispatch_uid, _make_id(sender)) else: lookup_key = (_make_id(receiver), _make_id(sender)) if weak: receiver = saferef.safeRef(receiver, onDelete=self._remove_receiver) self.lock.acquire() try: for r_key, _ in self.receivers: if r_key == lookup_key: break else: self.receivers.append((lookup_key, receiver)) finally: self.lock.release() def disconnect(self, receiver=None, sender=None, weak=True, dispatch_uid=None): """ Disconnect receiver from sender for signal. If weak references are used, disconnect need not be called. The receiver will be remove from dispatch automatically. Arguments: receiver The registered receiver to disconnect. May be none if dispatch_uid is specified. sender The registered sender to disconnect weak The weakref state to disconnect dispatch_uid the unique identifier of the receiver to disconnect """ if dispatch_uid: lookup_key = (dispatch_uid, _make_id(sender)) else: lookup_key = (_make_id(receiver), _make_id(sender)) self.lock.acquire() try: for index in xrange(len(self.receivers)): (r_key, _) = self.receivers[index] if r_key == lookup_key: del self.receivers[index] break finally: self.lock.release() def send(self, sender, **named): """ Send signal from sender to all connected receivers. 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. Arguments: sender The sender of the signal Either a specific object or None. named Named arguments which will be passed to receivers. Returns a list of tuple pairs [(receiver, response), ... ]. """ responses = [] if not self.receivers: return responses for receiver in self._live_receivers(_make_id(sender)): response = receiver(signal=self, sender=sender, **named) responses.append((receiver, response)) return responses def send_robust(self, sender, **named): """ Send signal from sender to all connected receivers catching errors. Arguments: sender The sender of the signal. Can be any python object (normally one registered with a connect if you actually want something to occur). named Named arguments which will be passed to receivers. These arguments must be a subset of the argument names defined in providing_args. Return a list of tuple pairs [(receiver, response), ... ]. May raise DispatcherKeyError. If any receiver raises an error (specifically any subclass of Exception), the error instance is returned as the result for that receiver. """ responses = [] if not self.receivers: return responses # Call each receiver with whatever arguments it can accept. # Return a list of tuple pairs [(receiver, response), ... ]. for receiver in self._live_receivers(_make_id(sender)): try: response = receiver(signal=self, sender=sender, **named) except Exception as err: responses.append((receiver, err)) else: responses.append((receiver, response)) return responses def _live_receivers(self, senderkey): """ Filter sequence of receivers to get resolved, live receivers. This checks for weak references and resolves them, then returning only live receivers. """ none_senderkey = _make_id(None) receivers = [] for (receiverkey, r_senderkey), receiver in self.receivers: if r_senderkey == none_senderkey or r_senderkey == senderkey: if isinstance(receiver, WEAKREF_TYPES): # Dereference the weak reference. receiver = receiver() if receiver is not None: receivers.append(receiver) else: receivers.append(receiver) return receivers def _remove_receiver(self, receiver): """ Remove dead receivers from connections. """ self.lock.acquire() try: to_remove = [] for key, connected_receiver in self.receivers: if connected_receiver == receiver: to_remove.append(key) for key in to_remove: last_idx = len(self.receivers) - 1 # enumerate in reverse order so that indexes are valid even # after we delete some items for idx, (r_key, _) in enumerate(reversed(self.receivers)): if r_key == key: del self.receivers[last_idx-idx] finally: self.lock.release() def receiver(signal, **kwargs): """ A decorator for connecting receivers to signals. Used by passing in the signal (or list of signals) and keyword arguments to connect:: @receiver(post_save, sender=MyModel) def signal_receiver(sender, **kwargs): ... @receiver([post_save, post_delete], sender=MyModel) def signals_receiver(sender, **kwargs): ... """ def _decorator(func): if isinstance(signal, (list, tuple)): for s in signal: s.connect(func, **kwargs) else: signal.connect(func, **kwargs) return func return _decorator