What's a process in Elixir?

To learn what a process is in Elixir, you must first know what a function is.

For example, IO.puts/1 is a function that writes something to the screen. The function is called puts, it is in the IO module (input I and output O), and it takes one argument:

iex(1)> IO.puts("Adolfo")
Adolfo
:ok

If all goes well, it returns the :ok atom .
One function that lets you spawn a process is Kernel.spawn/1.

Again, the name is spawn. It's part of the Kernel module and takes one argument.

Can I do

Kernel.spawn(IO.puts("Adolfo"))

?
No!

Let's start simple: every function that is part of the Kernel module doesn't need the module name before it.
You just call

elixir
spawn(IO.puts("Adolfo"))
`

It will still be wrong, but with fewer letters.

What Kernel.spawn/1` gets is an arity 0 function, i.e., one that takes no arguments.
How do we do that?
Like this:

fn -> 1 end

The above function has no name (anonymous) and returns 1.

But see in the image that if you spawn it, nothing interesting happens:

First, see that

fn -> 1 end

returned some sort of "code" that identifies the function:

#Function<43.3316493/0 in :erl_eval.expr/6>

and

spawn(fn -> 1 end)

returned a PID, a Process IDentifier:

#PID<0.120.0>

I can assign this PID to a variable:

iex(1)> pid = spawn(fn -> 1 end)
#PID<0.110.0>

And then ask if the process that was spawned is alive:

iex(2)> Process.alive?(pid)
false

It is not alive because it was a very fast function, which only returned 1.
I can, for example, make the process "sleep" for 10 seconds before returning 1.

iex(3)> pid = spawn(fn -> Process.sleep(10000); 1 end)
#PID<0.113.0>

If I quickly ask if the process, whose identifier is in the pid variable, is alive, the answer is yes.

iex(4)> Process.alive?(pid)
true

But if I ask again after 10 seconds, the answer is no.

iex(5)> Process.alive?(pid)
false

If I do this here

iex(6)> pid = spawn(fn -> Process.sleep(10000); IO.puts("Adolfo") end)
#PID<0.117.0>
Adolfo

it will take 10 seconds for "Adolfo" to be written to the screen.

Whereas if I do the following, it will be immediate for "Adolfo" to appear on the screen.

iex(7)> pid = spawn(fn -> IO.puts("Adolfo") end)
Adolfo
#PID<0.119.0>

Anyway, this is just the basics of the basics. Read more at
https://elixirschool.com/pt/lessons/intermediate/concurrency

Or in the Getting Started of the Elixir language
https://elixir-lang.org/getting-started/processes.html

I did all this without even mentioning send and receive.

Finally: a process in Elixir is a processing unit that performs a function.

Comments

[Alfred Reinold Baudisch]

That's a really good, concise writeup, Adolfo. I'll follow people to this article when they ask me about this.

By the way, I came up to your post via RSS, as I am consuming both of your dev.to RSS feeds.

[Adolfo Neto]

Thanks!

[Adolfo Neto]

"A process is an isolated entity where code execution happens and they are the base to design software systems taking advantage of the BEAM ." erlang-solutions.com/blog/understa...

[Vuyo Nyembezi]

In Elixir, all code runs inside processes. Processes are isolated from each other, run concurrent to one another and communicate via message passing. Processes are not only the basis for concurrency in Elixir, but they also provide the means for building distributed and fault-tolerant programs.

They are the guards of functionality they keep everything going

[Adolfo Neto]

Thanks! Excellent comment!

[Adolfo Neto]

"Multiple processes or threads on a single time-sliced CPU might exhibit concurrency but not parallelism. Parallelism is about multiple tasks that literally run at the same time on hardware with multiple computing resources like a multi-core CPU." https://blog.finiam.com/blog/how-to-build-concurrent-and-resilient-service-in-elixir?utm_medium=email&utm_source=elixir-radar