Ticket #1680: 0001-add-classes-sugar.dispatch.RelayedSignal-and-sugar.d.patch

src/sugar/dispatch/__init__.py

@@ -6 +6 @@
 Heavily modified for Django's purposes.
 """
 
-from sugar.dispatch.dispatcher import Signal
+from sugar.dispatch.dispatcher import Signal, RelayedSignal, DbusSignal

src/sugar/dispatch/dispatcher.py

@@ -4 +4 @@
 except NameError:
     from sets import Set as set # Python 2.3 fallback
 
+import dbus
+
 from sugar.dispatch import saferef
 
 WEAKREF_TYPES = (weakref.ReferenceType, saferef.BoundMethodWeakref)
@@ -189 +191 @@
             for idx, (r_key, _) in enumerate(self.receivers):
                 if r_key == key:
                     del self.receivers[idx]
+
+
+class RelayedSignal(Signal):
+    """Base class for signals relayed from another source.
+
+    Will attach to / detach from the source if there are
+    any / no listeners.
+    """
+
+    def __init__(self, *args, **kwargs):
+        Signal.__init__(self, *args, **kwargs)
+        self._attached = False
+
+    def _attach(self):
+        """Override in subclass to attach to source."""
+        raise NotImplementedError()
+
+    def _detach(self):
+        """Override in subclass to detach from source."""
+        raise NotImplementedError()
+
+    def connect(self, *args, **kwargs):
+        Signal.connect(self, *args, **kwargs)
+        if not self._attached:
+            self._attach()
+            self._attached = True
+
+    def disconnect(self, *args, **kwargs):
+        Signal.disconnect(self, *args, **kwargs)
+        if self._attached and not self.receivers:
+            self._detach()
+            self._attached = False
+
+
+class DbusSignal(RelayedSignal):
+    """"Relay for DBus signals."""
+
+    def __init__(self, signal_name, signal_args, iface=None, bus=None,
+        iface_name=None, service_name=None, path=None):
+        """Set up a relay for given DBus signal.
+
+        Mandatory arguments:
+        signal_name -- name of the DBus signal to relay
+        signal_args -- names of the arguments the signal passes
+
+        Keyword arguments:
+        bus -- dbus.Bus instance
+        iface_name -- DBus interface name
+        service_name -- DBus service name
+        path -- DBus path
+
+        Either iface or at least bus (and optionally iface_name, service_name
+        and path) must be given.
+        """
+        if iface and (bus or iface_name or service_name or path):
+            raise ValueError('Ambiguous: both iface and'
+                ' bus/iface_name/service_name/path given.')
+        elif not (iface or bus):
+            raise ValueError('Either iface or bus must be given.')
+
+        self._signal_name = signal_name
+        self._signal_args = signal_args
+        self._iface = iface
+        self._bus = bus
+        self._iface_name = iface_name
+        self._service_name = service_name
+        self._path = path
+        self._match = None
+        RelayedSignal.__init__(self, signal_args)
+
+    def _attach(self):
+        if self._iface:
+            self._match = self._iface.connect_to_signal(self._signal_name,
+                self._relay)
+        else:
+            self._match = self._bus.add_signal_receiver(self._relay,
+                signal_name=self._signal_name, dbus_interface=self._iface_name,
+                bus_name=self._service_name, path=self._path)
+
+    def _detach(self):
+        self._match.remove()
+
+    def _relay(self, *args):
+        """Relay signal.
+
+        Positional arguments are mapped to signal_args in order.
+        """
+        self.send(None, **dict(
+            [(name, value) for (name, value) in zip(self._signal_args, args)]))