events: add support for per-instance handlers

doc/qubes-events.rst

@@ -40,29 +40,7 @@ which the event was fired and the second one is the event name. The rest are
 passed from :py:meth:`qubes.events.Emitter.fire_event` as described previously.
 One callable can handle more than one event.
 
-The easiest way to hook an event is to invoke
+The easiest way to hook an event is to use
-:py:meth:`qubes.events.Emitter.add_handler` classmethod.
-
-.. code-block:: python
-
-   import qubes.events
-
-   class MyClass(qubes.events.Emitter):
-       pass
-
-   def event_handler(subject, event):
-       if event == 'event1':
-           print('Got event 1')
-       elif event == 'event2':
-           print('Got event 2')
-
-   MyClass.add_handler('event1', event_handler)
-   MyClass.add_handler('event2', event_handler)
-
-   o = MyClass()
-   o.fire_event('event1')
-
-If you wish to define handler in the class definition, the best way is to use
 :py:func:`qubes.events.handler` decorator.
 
 .. code-block:: python
@@ -80,7 +58,10 @@ If you wish to define handler in the class definition, the best way is to use
    o = MyClass()
    o.fire_event('event1')
 
+Note that your handler will be called for all instances of this class.
+
 .. TODO: extensions
+.. TODO: add/remove_handler
 
 
 Handling events with variable signature
@@ -100,7 +81,8 @@ every other python function with variable signature.
        else:
            print('Property {} changed {!r} -> {!r}'.format(name, oldvalue, newvalue))
 
-   qubes.Qubes.add_handler('property-set:default_netvm')
+   app = qubes.Qubes()
+   app.add_handler('property-set:default_netvm')
 
 If you expect :py:obj:`None` to be a reasonable value of the property, you have
 a problem. One way to solve it is to invent your very own, magic
@@ -117,7 +99,8 @@ a problem. One way to solve it is to invent your very own, magic
        else:
            print('Property {} changed {!r} -> {!r}'.format(name, oldvalue, newvalue))
 
-   qubes.Qubes.add_handler('property-set:default_netvm')
+   app = qubes.Qubes()
+   app.add_handler('property-set:default_netvm')
 
 There is no possible way of collision other than intentionally passing this very
 object (not even passing similar featureless ``object()``), because ``is``

qubes/events.py

@@ -27,6 +27,8 @@ etc.
 
 import collections
 
+import itertools
+
 
 def handler(*events):
     '''Event handler decorator factory.
@@ -88,7 +90,7 @@ class EmitterMeta(type):
                 continue
 
             for event in attr.ha_events:
-                cls.add_handler(event, attr)
+                cls.__handlers__[event].add(attr)
 
 
 class Emitter(object, metaclass=EmitterMeta):
@@ -102,10 +104,10 @@ class Emitter(object, metaclass=EmitterMeta):
         super(Emitter, self).__init__(*args, **kwargs)
         if not hasattr(self, 'events_enabled'):
             self.events_enabled = False
+        self.__handlers__ = collections.defaultdict(set)
 
 
-    @classmethod
+    def add_handler(self, event, func):
-    def add_handler(cls, event, func):
         '''Add event handler to subject's class.
 
         This is class method, it is invalid to call it on object instance.
@@ -115,10 +117,9 @@ class Emitter(object, metaclass=EmitterMeta):
         '''
 
         # pylint: disable=no-member
-        cls.__handlers__[event].add(func)
+        self.__handlers__[event].add(func)
 
-    @classmethod
+    def remove_handler(self, event, func):
-    def remove_handler(cls, event, func):
         '''Remove event handler from subject's class.
 
         This is class method, it is invalid to call it on object instance.
@@ -131,8 +132,7 @@ class Emitter(object, metaclass=EmitterMeta):
         '''
 
         # pylint: disable=no-member
-        cls.__handlers__[event].remove(func)
+        self.__handlers__[event].remove(func)
-
 
     def _fire_event_in_order(self, order, event, kwargs):
         '''Fire event for classes in given order.
@@ -145,12 +145,14 @@ class Emitter(object, metaclass=EmitterMeta):
             return []
 
         effects = []
-        for cls in order:
+        for i in order:
-            if not hasattr(cls, '__handlers__'):
+            try:
+                handlers_dict = i.__handlers__
+            except AttributeError:
                 continue
-            handlers = cls.__handlers__[event]
+            handlers = handlers_dict.get(event, set())
-            if '*' in cls.__handlers__:
+            if '*' in handlers_dict:
-                handlers = cls.__handlers__['*'] | handlers
+                handlers = handlers_dict['*'] | handlers
             for func in sorted(handlers,
                     key=(lambda handler: hasattr(handler, 'ha_bound')),
                     reverse=True):
@@ -159,7 +161,6 @@ class Emitter(object, metaclass=EmitterMeta):
                     effects.extend(effect)
         return effects
 
-
     def fire_event(self, event, **kwargs):
         '''Call all handlers for an event.
 
@@ -178,7 +179,8 @@ class Emitter(object, metaclass=EmitterMeta):
         events.
         '''
 
-        return self._fire_event_in_order(reversed(self.__class__.__mro__),
+        return self._fire_event_in_order(
+            itertools.chain(reversed(self.__class__.__mro__), (self,)),
             event, kwargs)
 
 
@@ -199,5 +201,6 @@ class Emitter(object, metaclass=EmitterMeta):
         events.
         '''
 
-        return self._fire_event_in_order(self.__class__.__mro__,
+        return self._fire_event_in_order(
+            itertools.chain((self,), self.__class__.__mro__),
             event, kwargs)

qubes/ext/__init__.py

@@ -45,11 +45,12 @@ class Extension(object):
 
                 if attr.ha_vm is not None:
                     for event in attr.ha_events:
-                        attr.ha_vm.add_handler(event, attr)
+                        attr.ha_vm.__handlers__[event].add(attr)
                 else:
                     # global hook
                     for event in attr.ha_events:
-                        qubes.Qubes.add_handler(event, attr)
+                        # pylint: disable=no-member
+                        qubes.Qubes.__handlers__[event].add(attr)
 
         return cls._instance
 

qubes/tests/events.py

@@ -103,3 +103,35 @@ class TC_00_Emitter(qubes.tests.QubesTestCase):
         self.assertEqual(testevent_fired[0], 3)
         emitter.fire_event('bar')
         self.assertEqual(testevent_fired[0], 4)
+
+    def test_005_instance_handlers(self):
+        class TestEmitter(qubes.events.Emitter):
+            @qubes.events.handler('testevent')
+            def on_testevent_1(self, event):
+                yield 'testevent_1'
+
+        def on_testevent_2(subject, event):
+            yield 'testevent_2'
+
+        emitter = TestEmitter()
+        emitter.add_handler('testevent', on_testevent_2)
+        emitter.events_enabled = True
+
+        emitter2 = TestEmitter()
+        emitter2.events_enabled = True
+
+        with self.subTest('fire_event'):
+            effect = emitter.fire_event('testevent')
+            effect2 = emitter2.fire_event('testevent')
+            self.assertEqual(list(effect),
+                ['testevent_1', 'testevent_2'])
+            self.assertEqual(list(effect2),
+                ['testevent_1'])
+
+        with self.subTest('fire_event_pre'):
+            effect = emitter.fire_event_pre('testevent')
+            effect2 = emitter2.fire_event_pre('testevent')
+            self.assertEqual(list(effect),
+                ['testevent_2', 'testevent_1'])
+            self.assertEqual(list(effect2),
+                ['testevent_1'])