When the socket layer makes calls into the protocol layer, it ensures that it has exclusive access for the data structures that are Shared between the two layers.
Because nonblocking channels give no indication when a message has been fully read, we are forced to handle this at the protocol layer.
In the case of receiving out-of-band data, the protocol layer checks for different conditions to validate that the received data is OOB, and then returns it to the socket layer.
