问题
What confuses me is that given that sockets are bi-directional, why can't I just open 1 socket with socket() on the client and one on the server and let them communicate over this single socket?
What would be a common use case that I would need a pair of sockets?
回答1:
So what is the common use case that I would need a pair of sockets?
Typically that you want bidirectional communication between a parent and child process (or sometimes between threads in the same process).
It's like a bidirectional equivalent of pipe, and avoids exposing an AF_UNIX path, or any other publicly-visible address, for something internal to your program.
There's a worked example here.
回答2:
socketpair creates two sockets which are already connected to each other. A common use case is the communication between a parent and a child process: the parent creates the socket pair, forks the child and then child and parent can communicate through their end of the socket pair with each other.
来源：https://stackoverflow.com/questions/64214231/why-do-i-need-socketpair-when-i-have-socket-with-af-unix