gen_server

Much of the work you think of as the core of a program - calculating results, storing information, and preparing replies - will fit neatly into the gen_server behavior. It provides a core set of methods that let you set up a process, respond to requests, end the process gracefully, and even pass state to a new process if this one needs to be upgraded in place. (Laurent 2017, 148)

gen_server is a generic server process that implements a standard set of interface functions and functionality for tracing and error reporting, it also fits an OTP supervision tree.

The gen_server behaviour interface contains six functions:

• init/1
• handle_call/3: Sends a synchronous message to a gen_server process and waits for a reply.
• handle_cast/2: Sends an asynchronous message to a gen_server process.
• handle_info/2: Handles messages sent to a gen_server container that were not sent using one of the call or cast functions.
• terminate/2: When a gen_server shuts down, this callback is raised to give you a chance to clean things up.
• code_change/3