How to create module based Tasks

luizamboni · October 12, 2017, 6:33am

Im trying reproduce the example of module-based task like the example

https://hexdocs.pm/elixir/Task.html#module-supervised-tasks

in my try

luizamboni/elixir-study/blob/master/otp/5-task/module-task.exs

defmodule TaskModule do

  use Task

  def start_link(arg) do
    Task.start_link(__MODULE__, :run, [arg])
  end

  def run(arg) do
    # IO.inspect arg
    IO.puts arg + 2
  end

end


Supervisor.start_link([
  # { module, argumnet }
  { TaskModule, 3 }], 
  strategy: :one_for_one

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What is wrong ?
Thanks!

NobbZ · October 12, 2017, 6:35am

Can you show your supervisor as well?

luizamboni · October 12, 2017, 7:58pm

i m not using module based Supervisor

NobbZ · October 12, 2017, 8:02pm

Sou you are just doing elixir yourscript?

Then your script ends even before the supervisor has fully started.

Or what exactly is your problem?

luizamboni · October 12, 2017, 8:15pm

ow…excuse-me i forgive to explain the error !
I got this error in shell:

** (UndefinedFunctionError) function Task.__using__/1 is undefined or private
(elixir) Task.__using__([])
module-task.exs:3: (module)
module-task.exs:1: (file)

NobbZ · October 12, 2017, 8:20pm

Probably your elixir is to old.

I checked branches and Task.__using__/1 only exists in 1.5 branch.

luizamboni · October 12, 2017, 8:45pm

the version is 1.4.2

NobbZ · October 12, 2017, 8:48pm

As you can see, Task.__using__/1 does not exist in v1.4.2, so if you want to use it, you need to update.

github.com

elixir-lang/elixir/blob/v1.4.2/lib/elixir/lib/task.ex

defmodule Task do
  @moduledoc """
  Conveniences for spawning and awaiting tasks.

  Tasks are processes meant to execute one particular
  action throughout their lifetime, often with little or no
  communication with other processes. The most common use case
  for tasks is to convert sequential code into concurrent code
  by computing a value asynchronously:

      task = Task.async(fn -> do_some_work() end)
      res  = do_some_other_work()
      res + Task.await(task)

  Tasks spawned with `async` can be awaited on by their caller
  process (and only their caller) as shown in the example above.
  They are implemented by spawning a process that sends a message
  to the caller once the given computation is performed.

  Besides `async/1` and `await/2`, tasks can also be

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Also you can take a look at the documentation of 1.4.2, the example there does not mention any use of use

https://hexdocs.pm/elixir/1.4.2/Task.html

luizamboni · October 12, 2017, 8:51pm

i update to 1.5.2 like a doc i m read
But now i got other error:

** (UndefinedFunctionError) function Supervisor.start_link/1 is undefined or private. Did you mean one of:

  * start_link/2
  * start_link/3

but It is exact like the doc…

luizamboni · October 12, 2017, 9:40pm

Supervisor.start_link/1 not exists…

This doc like wrong…

net · October 12, 2017, 9:44pm

The docs are wrong.

number = 5
Supervisor.start_link([{TaskModule, number}], strategy: :one_for_one)

Since your module takes a number and adds 2 to it, we’re passing in a number (5) as the argument. You can pass in whatever you like.

See also: https://hexdocs.pm/elixir/Supervisor.html

luizamboni · October 12, 2017, 9:48pm

thank you !
this forum is observed by core team ?
We can alert about this.
Is a trouble for newbies

OvermindDL1 · October 12, 2017, 9:49pm

It is (mostly) but it is still good to submit an issue ticket on github.
Or better yet, a PR! ^.^