Final answer:
The backlog argument in the listen function controls the length of the pending connection queue. It specifies the maximum number of connections that can wait in the queue.
Step-by-step explanation:
The goal of the backlog argument in the listen function is to control the length of the pending connection queue. When a socket is in passive mode, meaning it is expecting connections, it has a queue where these incoming connections are placed. The backlog argument specifies the maximum length of this queue.
For example, let's say we have a server socket that can handle a maximum of 10 connections. If the backlog is set to 5, it means that the server socket can have 5 connections waiting in the queue for the program to accept them, while the other 5 connections will be rejected.
Setting an appropriate backlog value is important to ensure that the server does not become overwhelmed with too many pending connections and that it can handle incoming connections efficiently.