import weakref
import threading
from django.dispatch import saferef
from django.utils.six.moves import xrange
WEAKREF_TYPES = (weakref.ReferenceType, saferef.BoundMethodWeakref)
def _make_id(target):
if hasattr(target, '__func__'):
return (id(target.__self__), id(target.__func__))
return id(target)
NONE_ID = _make_id(None)
# A marker for caching
NO_RECEIVERS = object()
[docs]class Signal(object):
"""
Base class for all signals
Internal attributes:
receivers
{ receriverkey (id) : weakref(receiver) }
"""
def __init__(self, providing_args=None, use_caching=False):
"""
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()
self.use_caching = use_caching
# For convenience we create empty caches even if they are not used.
# A note about caching: if use_caching is defined, then for each
# distinct sender we cache the receivers that sender has in
# 'sender_receivers_cache'. The cache is cleaned when .connect() or
# .disconnect() is called and populated on send().
self.sender_receivers_cache = weakref.WeakKeyDictionary() if use_caching else {}
[docs] 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.configured and 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)
with self.lock:
for r_key, _ in self.receivers:
if r_key == lookup_key:
break
else:
self.receivers.append((lookup_key, receiver))
self.sender_receivers_cache.clear()
[docs] 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))
with self.lock:
for index in xrange(len(self.receivers)):
(r_key, _) = self.receivers[index]
if r_key == lookup_key:
del self.receivers[index]
break
self.sender_receivers_cache.clear()
def has_listeners(self, sender=None):
return bool(self._live_receivers(sender))
[docs] 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 or self.sender_receivers_cache.get(sender) is NO_RECEIVERS:
return responses
for receiver in self._live_receivers(sender):
response = receiver(signal=self, sender=sender, **named)
responses.append((receiver, response))
return responses
[docs] 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 or self.sender_receivers_cache.get(sender) is NO_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(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, sender):
"""
Filter sequence of receivers to get resolved, live receivers.
This checks for weak references and resolves them, then returning only
live receivers.
"""
receivers = None
if self.use_caching:
receivers = self.sender_receivers_cache.get(sender)
# We could end up here with NO_RECEIVERS even if we do check this case in
# .send() prior to calling _live_receivers() due to concurrent .send() call.
if receivers is NO_RECEIVERS:
return []
if receivers is None:
with self.lock:
senderkey = _make_id(sender)
receivers = []
for (receiverkey, r_senderkey), receiver in self.receivers:
if r_senderkey == NONE_ID or r_senderkey == senderkey:
receivers.append(receiver)
if self.use_caching:
if not receivers:
self.sender_receivers_cache[sender] = NO_RECEIVERS
else:
# Note, we must cache the weakref versions.
self.sender_receivers_cache[sender] = receivers
non_weak_receivers = []
for receiver in receivers:
if isinstance(receiver, WEAKREF_TYPES):
# Dereference the weak reference.
receiver = receiver()
if receiver is not None:
non_weak_receivers.append(receiver)
else:
non_weak_receivers.append(receiver)
return non_weak_receivers
def _remove_receiver(self, receiver):
"""
Remove dead receivers from connections.
"""
with self.lock:
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]
self.sender_receivers_cache.clear()
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
Oct 03, 2017