'Restore a saved snapshot of current process from file
Warning: this is not thread safe, do not use with multithread program
Args:
- file: saved snapshot
Returns:
- Bool'

def restore_snapshot(self, filename=None):

    if (not filename):
        filename = self.get_config_filename('snapshot')
    fd = open(filename, 'rb')
    snapshot = pickle.load(fd)
    return self.give_snapshot(snapshot)
