Task Drills

Mix.install([
  {:jason, "~> 1.4"},
  {:kino, "~> 0.8.0", override: true},
  {:youtube, github: "brooklinjazz/youtube"},
  {:hidden_cell, github: "brooklinjazz/hidden_cell"}
])

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Task Drills

Drills help you develop familiarity and muscle memory with syntax through repeated exercises. Unlike usual problems, Drills are not intended to develop problem solving skills, they are purely for developing comfort and speed.

This set of drills is for Tasks. Follow the instructions for each drill and complete them as quickly as you can.

Task.await/2

Use Task.async/1 and Task.await/2 to spawn a task process that returns any response.

Use Task.async/1 and Task.await/2 to spawn a task process that sleeps for six seconds. It should cause a timeout error.

Use Task.async/1 and Task.await/2 to spawn a task process that sleeps for six seconds. Provide a timeout value to Task.await/2 so that it properly awaits the response.

Task.yield/2

Use Task.async/1 and Task.yield/2 to spawn a task process that returns any response.

Slow Operation

# 1000 operations
{time, _result} = :timer.tc(fn -> Enum.map(1..10, fn int -> Process.sleep(1000) end) end)
time

{time, _result} =
  :timer.tc(fn ->
    # 1000 tasks
    # 1000 operations -> parallel
    tasks =
      Enum.map(1..10, fn int ->
        Task.async(fn ->
          IO.puts("starting task #{int}")
          Process.sleep(1000)
        end)
      end)

    Task.await_many(tasks)
  end)

10_009_225
1_001_494

Fast Operation

# 1000 operations
{time, _result} = :timer.tc(fn -> Enum.map(1..10, fn int -> int * 2 end) end)
time

{time, _result} =
  :timer.tc(fn ->
    # 1000 tasks
    # 1000 operations -> parallel
    tasks = Enum.map(1..10, fn int -> Task.async(fn -> int * 2 end) end)
    Task.await_many(tasks)
  end)

Use Task.async/1 and Task.yield/2 to spawn a task process that sleeps for six seconds and returns any response. Notice that the yield is nil.

Use Task.async/1 and Task.yield/2 to spawn a task process that sleeps for six seconds and returns any response. Provide a timeout value to Task.yield/2 so that it properly returns the response.

Use Task.async/1, Task.yield/2, and Task.shutdown/2 to spawn a task process that sleeps for six seconds. Shutdown the task process if it does not yield any value.

Task.await_many/2

Use Task.async/1 and Task.await_many/2 to spawn two task processes that both return a random number from 1..10.

Use Enum.map/2, Task.async/1, and Task.await_many/2 to spawn one hundred task processes that all return a random integer from 1..100.

Use Enum.map/2, Task.async/1, and Task.await_many/2 to spawn one hundred task processes that return a list doubled numbers from one to one hundred. i.e. [2, 4, 6, 8, ..., 198, 200].

Use Enum.map/2, Task.async/1, String.upcase/2, and Task.await_many/2 to concurrently capitalize every string in the list ["apple", "pear", "peaches"]

Task.Supervisor

Start a Supervisor with a child Task.Supervisor process named MyTaskSupervisor. You will use MyTaskSupervisor in all of the examples below that need a task supervisor.

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

Supervisor.start_link(children, strategy: :one_for_one)

Use Task.Supervisor.async/3 and Task.await/2 to start a supervised task process that returns a random number after sleeping for two seconds.

Use Enum.map/2, Task.Supervisor.async/3 and Task.await_many/2 to start one hundred supervised task processes that returns a list of doubled numbers from one 1..100. i.e. [2, 4, 6, 8, ..., 198, 200].

Use Task.Supervisor.start_child/3 to start a :temporary task that crashes after five seconds. :temporary is already the default :restart option.

Use Supervisor.which_children/1 after six seconds to demonstrate that a :temporary process is not restarted.

Use Task.Supervisor.start_child/3 with the restart: :transient option to start a :transient task that crashes after five seconds.

Use Supervisor.which_children/1 after six seconds to demonstrate that the :transient process is restarted.

Mark As Completed

file_name = Path.basename(Regex.replace(~r/#.+/, __ENV__.file, ""), ".livemd")

save_name =
  case Path.basename(__DIR__) do
    "reading" -> "task_drills_reading"
    "exercises" -> "task_drills_exercise"
  end

progress_path = __DIR__ <> "/../progress.json"
existing_progress = File.read!(progress_path) |> Jason.decode!()

default = Map.get(existing_progress, save_name, false)

form =
  Kino.Control.form(
    [
      completed: input = Kino.Input.checkbox("Mark As Completed", default: default)
    ],
    report_changes: true
  )

Task.async(fn ->
  for %{data: %{completed: completed}} <- Kino.Control.stream(form) do
    File.write!(
      progress_path,
      Jason.encode!(Map.put(existing_progress, save_name, completed), pretty: true)
    )
  end
end)

form

Commit Your Progress

Run the following in your command line from the curriculum folder to track and save your progress in a Git commit. Ensure that you do not already have undesired or unrelated changes by running git status or by checking the source control tab in Visual Studio Code.

$ git checkout -b task-drills-exercise
$ git add .
$ git commit -m "finish task drills exercise"
$ git push origin task-drills-exercise

Create a pull request from your task-drills-exercise branch to your solutions branch. Please do not create a pull request to the DockYard Academy repository as this will spam our PR tracker.

DockYard Academy Students Only:

Notify your teacher by including @BrooklinJazz in your PR description to get feedback. You (or your teacher) may merge your PR into your solutions branch after review.

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