Mix task spawning a process does nothing

Question

I created a mix task which spawns a process. It uses Flow, reads from a stream and writes into a file defined in a consumer.

At the end of the day it just spawn some processes.

If I run it through iex it works fine as long as I leave the shell running.

But if I launch it from the command line as a mix task nothing happens, how do you leave the process opened?

  use Flow

  def run([stream]) do
    specs = [{{ProdCon,[]},[]}]
    consumer = [{{Consumer,[]},[]}]

    stream
    |> Flow.from_enumerable()
    |> Flow.through_specs(specs)
    |> Flow.into_specs(consumer)
  end

Aleksei Matiushkin Aleksei Matiushkin · Accepted Answer · 2018-08-01T07:48:50

Spawn a Task doing the job and wait until it finishes with Task.yield/2:

use Flow

def run([stream]) do
  task = Task.async(fn ->

    specs = [{{ProdCon,[]},[]}]
    consumer = [{{Consumer,[]},[]}]

    stream
    |> Flow.from_enumerable()
    |> Flow.through_specs(specs)
    |> Flow.into_specs(consumer)

  end)

  case Task.yield(task, 3_600) do # wait 1 hour
    {:ok, result} -> result
    nil -> IO.puts("Failed to get a result :(")
  end
end

Mix task spawning a process does nothing

1 Answers