/usr/lib/python2.7/dist-packages/foolscap/observer.py is in python-foolscap 0.6.4-2.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 | # -*- test-case-name: foolscap.test_observer -*-
# many thanks to AllMyData for contributing the initial version of this code
from twisted.internet import defer
from foolscap import eventual
class OneShotObserverList(object):
"""A one-shot event distributor.
Subscribers can get a Deferred that will fire with the results of the
event once it finally occurs. The caller does not need to know whether
the event has happened yet or not: they get a Deferred in either case.
The Deferreds returned to subscribers are guaranteed to not fire in the
current reactor turn; instead, eventually() is used to fire them in a
later turn. Look at Mark Miller's 'Concurrency Among Strangers' paper on
erights.org for a description of why this property is useful.
I can only be fired once."""
def __init__(self):
self._fired = False
self._result = None
self._watchers = []
self.__repr__ = self._unfired_repr
def _unfired_repr(self):
return "<OneShotObserverList [%s]>" % (self._watchers, )
def _fired_repr(self):
return "<OneShotObserverList -> %s>" % (self._result, )
def whenFired(self):
if self._fired:
return eventual.fireEventually(self._result)
d = defer.Deferred()
self._watchers.append(d)
return d
def fire(self, result):
assert not self._fired
self._fired = True
self._result = result
for w in self._watchers:
eventual.eventually(w.callback, result)
del self._watchers
self.__repr__ = self._fired_repr
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