Tasks

Mix.install([
  {:kino, "~> 0.6.2"},
  {:factory, path: "./factory"}
])

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• Index

Tasks

Tasks generally behave as expected from within livebook.

task =
  Task.async(fn ->
    Process.sleep(1000)
    "result"
  end)

Task.await(task) |> IO.puts()

IO.puts("Execution is paused until task finishes")

task =
  Task.async(fn ->
    Process.sleep(7000)
    "result"
  end)

Task.await(task)

task =
  Task.async(fn ->
    Process.sleep(7000)
    "result"
  end)

Task.yield(task) |> IO.inspect(label: "yield after 5 second timeout")
Task.yield(task) |> IO.inspect(label: "yield after 7 seconds.")

Supervised Tasks

children = [
  {Task.Supervisor, name: :task_supervisor}
]

Supervisor.start_link(children, strategy: :one_for_one)

We can start tasks under a supervisor and see them as a list of children pids

Task.Supervisor.async(:task_supervisor, fn ->
  Process.sleep(10000)
end)

Task.Supervisor.children(:task_supervisor)

Visualizing tasks under the :task_supervisor.

Kino.animate(500, 0, fn _ ->
  tree = Kino.Process.sup_tree(:task_supervisor)
  {:cont, tree, 0}
end)

Linked tasks cause the parent process to crash when we terminate_child/2.

task =
  Task.Supervisor.async_nolink(:task_supervisor, fn ->
    Process.sleep(20000)
  end)

Task.shutdown(task)

pid = :c.pid(0, 522, 0)

Task.Supervisor.terminate_child(:task_supervisor, pid)

Visualizing Task Clusters

# Kino.animate(500, 0, fn _ ->
#   tree = Kino.Process.sup_tree(:task_supervisor)
#   {:cont, tree, 0}
# end)

# tasks =
#   Enum.map(1..10, fn i ->
#     Task.Supervisor.async(:task_supervisor, fn ->
#       Process.sleep(11000 - i * 1000)
#       i
#     end)
#   end)

# Task.await_many(tasks, 11000)

Key Takeaways (Conclusion)

You can use LiveBook to:

• Gain insight into OTP processes or alongside an existing application.
• Quickly develop OTP experiments and save examples for yourself in the future.
• Document projects or teach other developers.