def load(self):
        "Loads the state from the state file"
        try:
            if os.path.getsize(self.state_file) <= 1:
                raise IOError("File is empty.")
            with open(self.state_file) as fh:
                state = json.load(fh)
                assert isinstance(state, dict)
                self.hosts = state['hosts']
                self.stats = state['stats']
            for key in self.stats:
                self.stats[key]['open_requests'] = 0
        except (IOError, OSError):
            # There is no state file; start empty.
            self.hosts = {}
            self.stats = {}
Loads the state from the state file