System.at_exit

You're seeing just the function at_exit, go back to System module for more information.

Specs

at_exit((non_neg_integer() -> any())) :: :ok

Registers a program exit handler function.

Registers a function that will be invoked at the end of an Elixir script. A script is typically started via the command line via the elixir and mix executables.

The handler always executes in a different process from the one it was registered in. As a consequence, any resources managed by the calling process (ETS tables, open files, and others) won't be available by the time the handler function is invoked.

The function must receive the exit status code as an argument.

If the VM terminates programmatically, via System.stop/1, System.halt/1, or exit signals, the at_exit/1 callbacks are not executed.