Event-driven Model in C with Sockets

You definitely must read the following: http://www.kegel.com/c10k.html. That page is the perfect overview of event-driven and asynchronous techniques.

However, a quick & dirty answer: event-driven is neither non-blocking, nor asynchronous.

Event-driven means, that the process will monitor its file descriptors (and sockets), and act only when some event occurs on some descriptor (events are: data received, error, became writeable, ...).

BSD sockets have the "select()" function. When called, the OS will monitor the descriptors, and return to the process as soon as some event on one of the descriptors occurs.

However, the website above has much better descriptions (and details about the different APIs).

"what is the philosophy behind this model"

Event driven means there is no "monitoring", but that the event itself initiates the action.

Usually this is initiated by an interrupt, which is a signal to the system from an external device, or (in the case of a software interrupt) an asynchronous process.

https://en.wikipedia.org/wiki/Interrupt

Further reading seems to be here:

https://docs.oracle.com/cd/E19455-01/806-1017/6jab5di2m/index.html#sockets-40 - "Interrupt-Driven Socket I/O"

Also http://cs.baylor.edu/~donahoo/practical/CSockets/textcode.html has some examples of Interrupt-Driven Sockets, as well as other socket programming examples.

Event driven programming is based on an event loop. The loop simply waits for a new event, dispatches code to handle the event, then loops back to wait for the next event. In the case of sockets, you're talking about "asynchronous network programming". This involves select() or some other option like Kqueue() to wait for the events in the event loop. Sockets would need to be set to non blocking, so that when you read() or write() your code won't wait for the I/O to complete.

Asynchronous network programming can be very complex, and tricky to get right. Check out a couple of introductions here and here. I strongly suggest using a library such as libevent or liboop to get this right.