spawn/1

The spawn/1 function is a quick fire-and-forget way to start an asynchronous process.

fun = fn ->
  # spawn/1 takes an anonymous function and
  # returns the Process Identifier (PID) of the new process.
  #
  # A crash in the spawned process doesn't impact the spawning process.
  pid =
    spawn(fn ->
      IO.inspect("I'm alive!")
      raise "BOOM!"
    end)

  IO.inspect("Started #{inspect(pid)}")
  :timer.sleep(1)
  IO.inspect("Still alive 😎")
end

fun.()

"Started #PID<0.171.0>"
"I'm alive!"
** (RuntimeError) BOOM!
"Still alive 😎"

You can link two processes if you want both to die if one of them dies. So, if a parent process spawns a child process and we link them, the parent dies if the child process dies and vice versa. To “die” in this context means that one process sends an :EXIT message to the other process that contains an exit reason other than :normal.

fun = fn ->
  # Start a parent process unlinked to the outer process,
  # but linked to its child. When the child dies,
  # the parent dies too, but the outer process is unaffected.
  pid =
    spawn(fn ->
      IO.inspect("Parent is alive! Spawning child...")
      spawn_link(fn -> raise "BOOM!" end)
      :timer.sleep(1) # <- Wait for the child to start.
      IO.inspect("Parent is still here!") # <- Will not execute
    end)

  IO.inspect("Started parent at #{inspect(pid)}")
  :timer.sleep(1)
  IO.inspect("Still alive 😎")
end

fun.()

"Started parent at #PID<0.215.0>"
"Parent is alive! Spawning child..."
** (RuntimeError) BOOM!
"Still alive 😎"