What happens when we say “listen to a port”?

Question

When we start a server application, we always need to speicify the port number it listens to. But how is this \"listening mechanism\" implemented under the hood?

My cur

Answer 1

1. Your description is basically correct except for the blocking part. OSes normally use interrupts to handle I/O events like arriving network packets, so there is no need to block.
2. Yes, if too many connection attempts happen at the same time, some will get bounced. The number of connections to queue is specified when you call listen or its equivalent.
3. No, it is not. The OS raises an event on your control socket when a connection arrives. You may choose to block while waiting for this event, or you may use some nonblocking (select, poll/epoll) or asynchronous (overlapped I/O, completion ports) mechanism.