Django中的Signal代码详解

class Signal(object):  """  Base class for all signals  Internal attributes:    receivers      { receiverkey (id) : weakref(receiver) }  """  def __init__(self, providing_args=None, use_caching=False):    """    创建一个新的Signal    providing_args 参数，指定这个Siganl 在发出事件（调用send方法）时，可以提供给观察者的信息参数    比如 post_save（）会带上 对应的instance对象，以及update_fields等    """    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 {}    self._dead_receivers = False  def connect(self, receiver, sender=None, weak=True, dispatch_uid=None):    from django.conf import settings    if dispatch_uid:      lookup_key = (dispatch_uid, _make_id(sender))    else:      lookup_key = (_make_id(receiver), _make_id(sender))    if weak:      ref = weakref.ref      receiver_object = receiver      # Check for bound methods      # 构造弱引用的的receiver      if hasattr(receiver, '__self__') and hasattr(receiver, '__func__'):        ref = WeakMethod        receiver_object = receiver.__self__      if sys.version_info >= (3, 4):        receiver = ref(receiver)        weakref.finalize(receiver_object, self._remove_receiver)      else:        receiver = ref(receiver, self._remove_receiver)    with self.lock:      #clear掉 由于弱引用 已被垃圾回收期回收的receivers      self._clear_dead_receivers()      for r_key, _ in self.receivers:        if r_key == lookup_key:          break      else:        self.receivers.append((lookup_key, receiver))      self.sender_receivers_cache.clear()  def disconnect(self, receiver=None, sender=None, weak=True, dispatch_uid=None):    if dispatch_uid:      lookup_key = (dispatch_uid, _make_id(sender))    else:      lookup_key = (_make_id(receiver), _make_id(sender))    disconnected = False    with self.lock:      self._clear_dead_receivers()      for index in range(len(self.receivers)):        (r_key, _) = self.receivers[index]        if r_key == lookup_key:          disconnected = True          del self.receivers[index]          break      self.sender_receivers_cache.clear()    return disconnected  def has_listeners(self, sender=None):    return bool(self._live_receivers(sender))  def send(self, sender, **named):    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  def send_robust(self, sender, **named):    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:        if not hasattr(err, '__traceback__'):          err.__traceback__ = sys.exc_info()[2]        responses.append((receiver, err))      else:        responses.append((receiver, response))    return responses  def _clear_dead_receivers(self):    # Note: caller is assumed to hold self.lock.    if self._dead_receivers:      self._dead_receivers = False      new_receivers = []      for r in self.receivers:        if isinstance(r[1], weakref.ReferenceType) and r[1]() is None:          continue        new_receivers.append(r)      self.receivers = new_receivers  def _live_receivers(self, sender):    """    过滤掉 已经被 垃圾回收的receiver    """    receivers = None    # 如果使用了cache , 并且没有调用过_remove_receiver 函数 则去 sender_receivers_cache中查找    if self.use_caching and not self._dead_receivers:      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:        self._clear_dead_receivers()        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.ReferenceType):        # 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=None):    self._dead_receivers = True

# myapp/signals/handlers.pyfrom django.dispatch import receiverfrom django.core.signals import request_finished## decorators 方式绑定@receiver(request_finished, dispatch_uid="request_finished")def my_signal_handler(sender, **kwargs):  print("Request finished!================================")# 普通绑定方式def my_signal_handler(sender, **kwargs):  print("Request finished!================================")request_finished.connect(my_signal_handler)###################################################### 针对model 的signal from django.dispatch import receiverfrom django.db.models.signals import post_savefrom polls.models import MyModel@receiver(post_save, sender=MyModel, dispatch_uid="mymodel_post_save")def my_model_handler(sender, **kwargs): print('Saved: {}'.format(kwargs['instance'].__dict__))

# myapp/__init__pydefault_app_config = 'myapp.apps.MySendingAppConfig'

# myapp/apps.pyfrom django.apps import AppConfigclass MyAppConfig(AppConfig):  name = 'myapp'  def ready(self):    # signals are imported, so that they are defined and can be used    import myapp.signals.handlers

myapp.signals.signals.pyimportdjango.dispatchmy_signal = django.dispatch.Signal(providing_args=["my_signal_arg1", "my_signal_arg_2"])

# myapp/__init__pydefault_app_config = 'myapp.apps.MySendingAppConfig'myapp/apps.pyfrom django.apps import AppConfigclass MyAppConfig(AppConfig):  name = 'myapp'  def ready(self):    # signals are imported, so that they are defined and can be used    import myapp.signals.handlers

# myapp/views.pyfrom .signals.signals import my_signalmy_signal.send(sender="some function or class",        my_signal_arg1="something", my_signal_arg_2="something else"])

# myapp/signals/handlers.pyfrom django.dispatch import receiverfrom myapp.signals.signals import my_signal@receiver(my_signal, dispatch_uid="my_signal_receiver")def my_signal_handler(sender, **kwargs):  print('my_signal received')