Erlang/Elixir Interview Questions

Explain tail-call optimisation

When Beam(Erlang VM) sees a function calling itself as the last executable statement in a function, it simply jumps back to the start of the function. If the recursive call has arguments then these replace the original parameters.

Explain the crucial feature of Erlang/Elixir

The idea is to pack code into manageable portions executed independently and concurrently.

spawn vs spawn_link

spawn is a function provided by erlang which takes a single function as an argument and runs it.
spwan_link is similar to spawn except it creates a process and links it and all this is executed as an atomic operation.

Process.flag(:trap_exit, true) — explain

This converts exit signals from a linked process into a message by trapping the exit.

Monitor vs links

1. link is bidirectional i.e if any process dies the other is notified and vice versa. While monitors are uni-directional i.e lets a process spawn another process and be notified of its termination, not the other way round.
2. links cannot be stacked while monitors can.
3. links are used when one process cannot survive without the other. Monitors are needed to know when the other process exits and you want to be notified about it.

Define a node

It is simply Erlang VM called the Beam. Beam in itself is a little OS running on top of your OS.

Define OTP

OTP is a package that includes Erlang, a database(Mnesia) and an innumerable number of libraries like GenServer, GenEvent etc.

Define reductions

Reduction is a measure of the amount of work the server does. It is used in process scheduling as a way of making sure all processes get a fair share of the available CPU.

Define OTP GenServer

An OTP GenServer is just a regular Elixir process in which the message handling is abstracted out.

Define Supervisor

It is a process that uses the OTP supervisor behaviour. It is given a list of processes to monitor and is told what to do if a process dies and how to prevent restart loops.