I have multiple greenlets sending on a common socket. Is it guaranteed that each package sent via socket.sendall is well separated or do I have to acquire a lock before each call to sendall. So I want to prevent the following scenario: g1 sends ABCD g2 sends 1234 received data is mixed up, for example AB1234CD expected is either ABCD1234 or 1234ABCD Update After a look at the sourcecode I think this scenario cannot happen. But I have to use a lock because g1 or g2 can crash on the sendall. Can someone confirm this?