source file: /home/buildslave/tahoe/edgy/build/src/allmydata/util/observer.py
file stats: 54 lines, 54 executed: 100.0% covered
1. # -*- test-case-name: allmydata.test.test_observer -*-
2.
3. from twisted.internet import defer
4. from foolscap.eventual import eventually
5.
6. """The idiom we use is for the observed object to offer a method named
7. 'when_something', which returns a deferred. That deferred will be fired when
8. something happens. The way this is typically implemented is that the observed
9. has an ObserverList whose when_fired method is called in the observed's
10. 'when_something'."""
11.
12. class OneShotObserverList:
13. """A one-shot event distributor."""
14. def __init__(self):
15. self._fired = False
16. self._result = None
17. self._watchers = []
18. self.__repr__ = self._unfired_repr
19.
20. def _unfired_repr(self):
21. return "<OneShotObserverList [%s]>" % (self._watchers, )
22.
23. def _fired_repr(self):
24. return "<OneShotObserverList -> %s>" % (self._result, )
25.
26. def _get_result(self):
27. return self._result
28.
29. def when_fired(self):
30. if self._fired:
31. return defer.succeed(self._get_result())
32. d = defer.Deferred()
33. self._watchers.append(d)
34. return d
35.
36. def fire(self, result):
37. assert not self._fired
38. self._fired = True
39. self._result = result
40. self._fire(result)
41.
42. def _fire(self, result):
43. for w in self._watchers:
44. eventually(w.callback, result)
45. del self._watchers
46. self.__repr__ = self._fired_repr
47.
48. def fire_if_not_fired(self, result):
49. if not self._fired:
50. self.fire(result)
51.
52. class LazyOneShotObserverList(OneShotObserverList):
53. """
54. a variant of OneShotObserverList which does not retain
55. the result it handles, but rather retains a callable()
56. through which is retrieves the data if and when needed.
57. """
58. def __init__(self):
59. OneShotObserverList.__init__(self)
60.
61. def _get_result(self):
62. return self._result_producer()
63.
64. def fire(self, result_producer):
65. """
66. @param result_producer: a no-arg callable which
67. returns the data which is to be considered the
68. 'result' for this observer list. note that this
69. function may be called multiple times - once
70. upon initial firing, and potentially once more
71. for each subsequent when_fired() deferred created
72. """
73. assert not self._fired
74. self._fired = True
75. self._result_producer = result_producer
76. if self._watchers: # if not, don't call result_producer
77. self._fire(self._get_result())
78.
79. class ObserverList:
80. """A simple class to distribute events to a number of subscribers."""
81.
82. def __init__(self):
83. self._watchers = []
84.
85. def subscribe(self, observer):
86. self._watchers.append(observer)
87.
88. def unsubscribe(self, observer):
89. self._watchers.remove(observer)
90.
91. def notify(self, *args, **kwargs):
92. for o in self._watchers:
93. eventually(o, *args, **kwargs)