I'm using a DeferredSemaphore with a token count of 1 to control access to a serial port. I also have a GTK object for which I'd like the "in-use" property to change (and notify listeners) when the resource is in use. So far, I have something like this: ---- class SerialResource(gobject): # Property defs, etc def _acquire(self): # The "in-use" property is actually stored in self.taken self.taken = True self.notify('in-use') def _release(self, res): self.taken = False self.notify('in-use') return res def run(self, func, *args, **kargs): def wrapper(): self._acquire() res = func(*args, **kargs) return res d = self.sem.run(wrapper) d.addBoth(self._release) return d ---- I feel like there might be a simpler way to do this, but I just can't see it. Or is this as simple as I can make it? — Jason