SignalManager in scrapy

Scrapy中的信号量通过SignalManager类实现 #

class SignalManager(object):

    def __init__(self, sender=dispatcher.Anonymous):
        self.sender = sender

    def connect(self, receiver, signal, **kwargs):
        """
        Connect a receiver function to a signal.

        The signal can be any object, although Scrapy comes with some
        predefined signals that are documented in the :ref: `topics-signals`
        section.

        :param receiver: the function to be connected
        :type receiver: callable

        :param signal: the signal to connect to
        :type signal: object
        """
        kwargs.setdefault('sender', self.sender)
        return dispatcher.connect(receiver, signal, **kwargs)

SignalManager通过PyDispatcher来实现

from pydispatch import dispatcher
PyDispatcher官方文档介绍，PyDispatcher是一个在多个上下文中的多消费者-多生产者-信号处理机制。它主要为了改善包含多个application项目的开发。

receiver-register(registration)-signal(message)-sender #

首先理解 receiver-register(registration)-signal(message)-sender
receiver和sender即接受和发送方，接受需要一个注册的过程，定义接受的来源和类型。

features #

摘自官方文档

• 它集中管理分发消息，只要是function（callable objects）就可以作为receiver接受sender的signal
  • 注册时可以为“信任接受”任意sender，特别是 particular sender （预定义的sender，如scrapy中），或是匿名 message , 即sender为None
  • 注册时可以接受任意signal，特别时 particular signal （预定义的siganl，又如scrapy）
  • 单个signal可以被分发到所有可能的receiver，他们彼此间互不干扰
  • 无需为sender或receiver编写额外代码或继承父类（从而使他们变得dispatch-aware）, 任意类型可以为sender，任意callable类型可以为receiver。、
• 可能的话尽量使用对receiver尽量使用弱引用
  • object的生命周期不受注册的行为的影响，当object的生命周期结束时，registration也失效
  • 对实例方法的引用为弱引用
  • weak references can be disabled on a registration-by-registration basis
  • 允许丰富的signal类型，分发过程对signal不做处理
  • 允许发送包含允许被particular receiver处理和其他receiver处理的general messages

# set up receiver
from pydispatch import dispatcher
SIGNAL = 'my-first-signal'

def handle_event( sender ):
    """Simple event handler"""
    print 'Signal was sent by', sender
dispatcher.connect( handle_event, signal=SIGNAL, sender=dispatcher.Any )

# set up sender
first_sender = object()
# can be any callable object
second_sender = {}
def main( ):
    dispatcher.send( signal=SIGNAL, sender=first_sender )
    dispatcher.send( signal=SIGNAL, sender=second_sender )

End.💖

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Published 03 Aug 2018