events: add support for async event handlers

See documentation for details.

contrib/check-events

@@ -81,7 +81,7 @@ class EventVisitor(ast.NodeVisitor):
             # events this way
             return
 
-        if name.endswith('.fire_event') or name.endswith('.fire_event_pre'):
+        if name.endswith('.fire_event') or name.endswith('.fire_event_async'):
             # here we throw events; event name is the first argument; sometimes
             # it is expressed as 'event-stem:' + some_variable
             eventnode = node.args[0]

doc/qubes-events.rst

@@ -143,6 +143,75 @@ returned to the caller as list. The order of this list is undefined.
    effect = o.fire_event('event1')
 
 
+Asynchronous event handling
+---------------------------
+
+Event handlers can be defined as coroutine. This way they can execute long
+running actions without blocking the whole qubesd process. To define
+asynchronous event handler, annotate a coroutine (a function defined with
+`async def`, or decorated with `py:func:`asyncio.coroutine`) with
+py:func:`qubes.events.handler` decorator. By definition, order of
+such handlers is undefined.
+
+Asynchronous events can be fired using
+:py:meth:`qubes.events.Emitter.fire_event_async` method. It will handle both
+synchronous and asynchronous handlers. It's an error to register asynchronous
+handler (a coroutine) for synchronous event (the one fired with
+:py:meth:`qubes.events.Emitter.fire_event`) - it will result in
+:py:exc:`RuntimeError` exception.
+
+.. code-block:: python
+
+   import asyncio
+   import qubes.events
+
+   class MyClass(qubes.events.Emitter):
+       @qubes.events.handler('event1', 'event2')
+       @asyncio.coroutine
+       def event_handler(self, event):
+           if event == 'event1':
+               print('Got event 1, starting long running action')
+               yield from asyncio.sleep(10)
+               print('Done')
+
+   o = MyClass()
+   loop = asyncio.get_event_loop()
+   loop.run_until_complete(o.fire_event_async('event1'))
+
+Asynchronous event handlers can also return value - but only a collection, not
+yield individual values (because of python limitation):
+
+.. code-block:: python
+
+   import asyncio
+   import qubes.events
+
+   class MyClass(qubes.events.Emitter):
+       @qubes.events.handler('event1')
+       @asyncio.coroutine
+       def event_handler(self, event):
+            print('Got event, starting long running action')
+            yield from asyncio.sleep(10)
+            return ('result1', 'result2')
+
+       @qubes.events.handler('event1')
+       @asyncio.coroutine
+       def another_handler(self, event):
+            print('Got event, starting long running action')
+            yield from asyncio.sleep(10)
+            return ('result3', 'result4')
+
+       @qubes.events.handler('event1')
+       def synchronous_handler(self, event):
+            yield 'sync result'
+
+   o = MyClass()
+   loop = asyncio.get_event_loop()
+   # returns ['sync result', 'result1', 'result2', 'result3', 'result4'],
+   # possibly not in order
+   effects = loop.run_until_complete(o.fire_event_async('event1'))
+
+
 Module contents
 ---------------
 

qubes/events.py

@@ -24,7 +24,7 @@
 Events are fired when something happens, like VM start or stop, property change
 etc.
 '''
-
+import asyncio
 import collections
 
 import itertools
@@ -36,14 +36,14 @@ def handler(*events):
     To hook an event, decorate a method in your plugin class with this
     decorator.
 
-    It probably makes no sense to specify more than one handler for specific
-    event in one class, because handlers are not run concurrently and there is
-    no guarantee of the order of execution.
+    Some event handlers may be defined as coroutine. In such a case, *async*
+    should be set to :py:obj:``True``.
+    See appropriate event documentation for details.
 
     .. note::
         For hooking events from extensions, see :py:func:`qubes.ext.handler`.
 
-    :param str event: event type
+    :param str events: events
     '''
 
     def decorator(func):
@@ -141,13 +141,14 @@ class Emitter(object, metaclass=EmitterMeta):
         '''
 
         if not self.events_enabled:
-            return []
+            return [], []
 
         order = itertools.chain((self,), self.__class__.__mro__)
         if not pre_event:
             order = reversed(list(order))
 
         effects = []
+        async_effects = []
         for i in order:
             try:
                 handlers_dict = i.__handlers__
@@ -160,9 +161,11 @@ class Emitter(object, metaclass=EmitterMeta):
                     key=(lambda handler: hasattr(handler, 'ha_bound')),
                     reverse=True):
                 effect = func(self, event, **kwargs)
-                if effect is not None:
+                if asyncio.iscoroutinefunction(func):
+                    async_effects.append(effect)
+                elif effect is not None:
                     effects.extend(effect)
-        return effects
+        return effects, async_effects
 
     def fire_event(self, event, pre_event=False, **kwargs):
         '''Call all handlers for an event.
@@ -173,6 +176,13 @@ class Emitter(object, metaclass=EmitterMeta):
         (specified in class definition), then handlers from extensions. Aside
         from above, remaining order is undefined.
 
+        This method call only synchronous handlers. If any asynchronous
+        handler is registered for the event, :py:class:``RuntimeError`` is
+        raised.
+
+        .. seealso::
+            :py:meth:`fire_event_async`
+
         :param str event: event identifier
         :param pre_event: is this -pre- event? reverse handlers calling order
         :returns: list of effects
@@ -181,4 +191,46 @@ class Emitter(object, metaclass=EmitterMeta):
         events.
         '''
 
-        return self._fire_event(event, kwargs, pre_event=pre_event)
+        sync_effects, async_effects = self._fire_event(event, kwargs,
+            pre_event=pre_event)
+        if async_effects:
+            raise RuntimeError(
+                'unexpected async-handler(s) {!r} for sync event {!s}'.format(
+                    async_effects, event))
+        return sync_effects
+
+
+    @asyncio.coroutine
+    def fire_event_async(self, event, pre_event=False, **kwargs):
+        '''Call all handlers for an event, allowing async calls.
+
+        Handlers are called for class and all parent classes, in **reversed**
+        or **true** (depending on *pre_event* parameter)
+        method resolution order. For each class first are called bound handlers
+        (specified in class definition), then handlers from extensions. Aside
+        from above, remaining order is undefined.
+
+        This method call both synchronous and asynchronous handlers. Order of
+        asynchronous calls is, by definition, undefined.
+
+        .. seealso::
+            :py:meth:`fire_event`
+
+        :param str event: event identifier
+        :param pre_event: is this -pre- event? reverse handlers calling order
+        :returns: list of effects
+
+        All *kwargs* are passed verbatim. They are different for different
+        events.
+        '''
+
+        sync_effects, async_effects = self._fire_event(event,
+            kwargs, pre_event=pre_event)
+        effects = sync_effects
+        if async_effects:
+            async_tasks, _ = yield from asyncio.wait(async_effects)
+            for task in async_tasks:
+                effect = task.result()
+                if effect is not None:
+                    effects.extend(effect)
+        return effects

qubes/tests/__init__.py

@@ -159,6 +159,18 @@ class TestEmitter(qubes.events.Emitter):
         self.fired_events[(event, ev_kwargs)] += 1
         return effects
 
+    @asyncio.coroutine
+    def fire_event_async(self, event, pre_event=False, **kwargs):
+        effects = yield from super(TestEmitter, self).fire_event_async(
+            event, pre_event=pre_event, **kwargs)
+        ev_kwargs = frozenset(
+            (key,
+                frozenset(value.items()) if isinstance(value, dict) else value)
+            for key, value in kwargs.items()
+        )
+        self.fired_events[(event, ev_kwargs)] += 1
+        return effects
+
 
 def expectedFailureIfTemplate(templates):
     """

qubes/tests/events.py

@@ -18,6 +18,7 @@
 # with this program; if not, write to the Free Software Foundation, Inc.,
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 #
+import asyncio
 
 import qubes.events
 import qubes.tests
@@ -134,3 +135,36 @@ class TC_00_Emitter(qubes.tests.QubesTestCase):
                 ['testevent_2', 'testevent_1'])
             self.assertEqual(list(effect2),
                 ['testevent_1'])
+
+    def test_005_fire_for_effect_async(self):
+        class TestEmitter(qubes.events.Emitter):
+            @qubes.events.handler('testevent')
+            @asyncio.coroutine
+            def on_testevent_1(self, event):
+                pass
+
+            @qubes.events.handler('testevent')
+            @asyncio.coroutine
+            def on_testevent_2(self, event):
+                yield from asyncio.sleep(0.01)
+                return ['testvalue1']
+
+            @qubes.events.handler('testevent')
+            @asyncio.coroutine
+            def on_testevent_3(self, event):
+                return ('testvalue2', 'testvalue3')
+
+            @qubes.events.handler('testevent')
+            def on_testevent_4(self, event):
+                return ('testvalue4',)
+
+        loop = asyncio.get_event_loop()
+        emitter = TestEmitter()
+        emitter.events_enabled = True
+
+        effect = loop.run_until_complete(emitter.fire_event_async('testevent'))
+        loop.close()
+        asyncio.set_event_loop(None)
+
+        self.assertCountEqual(effect,
+            ('testvalue1', 'testvalue2', 'testvalue3', 'testvalue4'))