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94 lines
2.9 KiB
Python
94 lines
2.9 KiB
Python
# -*- test-case-name: allmydata.test.test_observer -*-
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from twisted.internet import defer
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from foolscap.api import eventually
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"""The idiom we use is for the observed object to offer a method named
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'when_something', which returns a deferred. That deferred will be fired when
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something happens. The way this is typically implemented is that the observed
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has an ObserverList whose when_fired method is called in the observed's
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'when_something'."""
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class OneShotObserverList:
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"""A one-shot event distributor."""
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def __init__(self):
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self._fired = False
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self._result = None
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self._watchers = []
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self.__repr__ = self._unfired_repr
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def _unfired_repr(self):
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return "<OneShotObserverList [%s]>" % (self._watchers, )
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def _fired_repr(self):
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return "<OneShotObserverList -> %s>" % (self._result, )
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def _get_result(self):
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return self._result
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def when_fired(self):
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if self._fired:
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return defer.succeed(self._get_result())
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d = defer.Deferred()
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self._watchers.append(d)
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return d
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def fire(self, result):
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assert not self._fired
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self._fired = True
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self._result = result
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self._fire(result)
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def _fire(self, result):
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for w in self._watchers:
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eventually(w.callback, result)
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del self._watchers
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self.__repr__ = self._fired_repr
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def fire_if_not_fired(self, result):
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if not self._fired:
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self.fire(result)
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class LazyOneShotObserverList(OneShotObserverList):
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"""
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a variant of OneShotObserverList which does not retain
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the result it handles, but rather retains a callable()
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through which is retrieves the data if and when needed.
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"""
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def __init__(self):
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OneShotObserverList.__init__(self)
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def _get_result(self):
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return self._result_producer()
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def fire(self, result_producer):
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"""
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@param result_producer: a no-arg callable which
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returns the data which is to be considered the
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'result' for this observer list. note that this
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function may be called multiple times - once
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upon initial firing, and potentially once more
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for each subsequent when_fired() deferred created
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"""
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assert not self._fired
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self._fired = True
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self._result_producer = result_producer
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if self._watchers: # if not, don't call result_producer
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self._fire(self._get_result())
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class ObserverList:
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"""A simple class to distribute events to a number of subscribers."""
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def __init__(self):
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self._watchers = []
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def subscribe(self, observer):
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self._watchers.append(observer)
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def unsubscribe(self, observer):
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self._watchers.remove(observer)
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def notify(self, *args, **kwargs):
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for o in self._watchers:
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eventually(o, *args, **kwargs)
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