Are parallel calls to send/recv on the same socket valid?

Question

1. Can we call send from one thread and recv from another on the same socket?
2. Can we call multiple sends parallely from different threads on the same socket?

Answer 1

The socket descriptor belongs to the process, not to a particular thread. Hence, it is possible to send/receive to/from the same socket in different threads, the OS will handle the synchronization.

However, if the order of sending/receiving is semantically significant, you yourself (respectively your code) have to ensure proper sequencing between the operations in the different threads - as is always the case with threads.