TaskAfter

This is a library to call a function after a set delay. Usage is as simple as: TaskAfter.task_after(500, fn -> do_something_after_500_ms() end)

Installation

• Available in Hex
• Documentation

Install this package by adding task_after to your list of dependencies in mix.exs:

def deps do
  [
    {:task_after, "~> 1.0.0"},
  ]
end

Global installation

To use this globally without needing to add it to your own supervision tree just add this to your configuration:

config :task_after, global_name: TaskAfter

Feel free to replace the global name of TaskAfter with anything you want. If the global name is unspecified then all usage of TaskAfter must have the :name or :pid options specified.

Local Installation

To use this locally to your application or to give distinct names so you can have different schedulars then just add the TaskAfter.Worker.start_link/1 to your supervision tree as normal, such as via:

children = [
  worker(TaskAfter.Worker, [[name: MyCustomName]]),
]

Note the 2 sets of list elements. You can have a nameless worker by leaving the name option out, such as:

children = [
  worker(TaskAfter.Worker, [[]]),
]

You will have to acquire the PID some other way, such as by querying your supervisor.

Usage

The main interface point is TaskAfter.task_after/2 and TaskAfter.task_after/3 where TaskAfter.task_after/2 just calls TaskAfter.task_after/3 with an empty set of options to use the defaults.

The arguments to TaskAfter.task_after/3 are, in this order:

1. timeout_after_ms -> integer millisecond timeout
2. callback -> The 0-arg callback function
3. opts -> Can be:
   • name: name | pid: pid -> Specify a non-global task handler, if unspecified that the application :global_name must be specified
   • id: id -> A unique id, if nil or unspecified then it is auto-generated
   • call_timeout: timeout -> Override the timeout on calling to the TaskAfter.Worker
   • no_return: true -> Do not return the id or error, just try to register and forget results otherwise
   • send_result: pid -> Sends the result of the task to the specified pid
   • send_result: :in_process -> Runs the task in the TaskAfter.Worker process to do internal work, do not use this

You can also cancel a task via TaskAfter.cancel_task_after/1 and TaskAfter.cancel_task_after/2 where TaskAfter.cancel_task_after/1 just defaults to having an empty opts list.

The arguments to TaskAfter.cancel_task_after/2 are, in this order:

1. task_id -> A task id
2. opts -> Can be:
   • name: name | pid: pid -> Specify a non-global task handler, if unspecified that the application :global_name must be specified
   • call_timeout: timeout -> Override the timeout on calling to the TaskAfter.Worker
   • no_return: true -> Do not return the id or error, just try to register and forget results otherwise
   • run_result: pid -> Sends the result of the task to the specified pid after running it as an async task while returning the Task
   • run_result: :in_process -> Runs the task in the TaskAfter.Worker process to do internal work, do not use this, returns the value directly though
   • run_result: :async -> Runs the task as an async task and dismisses the result while returning the Task
   • run_result: nil -> Default: Does not run the task now, just cancels it immediately, returns the callback function

You can change a task via TaskAfter.change_task_after/2.

The arguments to TaskAfter.change_task_after/2 are, in this order:

1. task_id -> A task ID
2. opts -> Can be:

• name: name | pid: pid -> Specify a non-global task handler, if unspecified that the application :global_name must be specified
• call_timeout: timeout -> Override the timeout on calling to the TaskAfter.Worker`
• no_return: true -> Do not return the id or error, just try to register and forget results otherwise
• callback: fun -> Change the callback to this function
• timeout_after_ms: timeout -> Change the timeout to this new value
• send_result: pid -> Sends the result of the task to the specified pid after running it as an async task
• send_result: :in_process -> Runs the task in the TaskAfter.Worker process to do internal work, do not use this
• send_result: :async -> Default: Runs the task as an async task and dismisses the result
• recreate: true -> If this is passed in then callback, timeout_after_ms, and send_result must be specified to be able to recreate the task if it is already elapsed.

Note: Of course if the task has already run then changing a setting on it won't do anything unless recreate: true is passed in.

Note: When recreate: true is used then callback, timeout_after_ms, and send_result can be passed in their value wrapped in a tagged :default tuple like timeout_after_ms: {:default, 500} and it will not change the existing value if not recreating but will use the value if it is.

They can be used as in these examples/tests:

  test "TaskAfter and forget" do
    s = self()
    assert {:ok, _auto_id} = TaskAfter.task_after(500, fn -> send(s, 42) end)
    assert_receive(42, 600)
  end

  test "TaskAfter and receive" do
    assert {:ok, _auto_id} = TaskAfter.task_after(500, fn -> 42 end, send_result: self())
    assert_receive(42, 600)
  end

  test "TaskAfter with custom id" do
    assert {:ok, :my_id} = TaskAfter.task_after(500, fn -> 42 end, id: :my_id, send_result: self())
    assert_receive(42, 600)
  end

  test "TaskAfter with custom id duplicate fails" do
    assert {:ok, :dup_id} = TaskAfter.task_after(500, fn -> 42 end, id: :dup_id, send_result: self())
    assert {:error, {:duplicate_id, :dup_id}} = TaskAfter.task_after(500, fn -> 42 end, id: :dup_id, send_result: self())
    assert_receive(42, 600)
  end

  test "TaskAfter lots of tasks" do
    assert {:ok, _} = TaskAfter.task_after(400, fn -> 400 end, send_result: self())
    assert {:ok, _} = TaskAfter.task_after(200, fn -> 200 end, send_result: self())
    assert {:ok, _} = TaskAfter.task_after(500, fn -> 500 end, send_result: self())
    assert {:ok, _} = TaskAfter.task_after(100, fn -> 100 end, send_result: self())
    assert {:ok, _} = TaskAfter.task_after(300, fn -> 300 end, send_result: self())
    assert {:ok, _} = TaskAfter.task_after(600, fn -> 600 end, send_result: self())
    assert_receive(100, 150)
    assert_receive(200, 150)
    assert_receive(300, 150)
    assert_receive(400, 150)
    assert_receive(500, 150)
    assert_receive(600, 150)
  end

  test "TaskAfter non-global by name" do
    assert {:ok, pid} = TaskAfter.Worker.start_link(name: :testing_name)
    {:ok, _auto_id} = TaskAfter.task_after(500, fn -> 42 end, send_result: self(), name: :testing_name)
    assert_receive(42, 600)
    GenServer.stop(pid)
  end

  test "TaskAfter non-global by pid" do
    assert {:ok, pid} = TaskAfter.Worker.start_link()
    assert {:ok, _auto_id} = TaskAfter.task_after(500, fn -> 42 end, send_result: self(), pid: pid)
    assert_receive(42, 600)
    GenServer.stop(pid)
  end

  test "TaskAfter in process (unsafe, can freeze the task worker if the task does not return fast)" do
    assert {:ok, pid} = TaskAfter.Worker.start_link()
    s = self()
    assert {:ok, _auto_id} = TaskAfter.task_after(500, fn -> send(s, self()) end, send_result: :in_process, pid: pid)
    assert_receive(^pid, 600)
    GenServer.stop(pid)
  end

  test "TaskAfter and cancel timer, do not run the callback" do
    cb = fn -> 42 end
    assert {:ok, auto_id} = TaskAfter.task_after(500, cb)
    assert {:ok, ^cb} = TaskAfter.cancel_task_after(auto_id)
  end

  test "TaskAfter and cancel timer, but its already been run or does not exist" do
    assert {:error, {:does_not_exist, :none}} = TaskAfter.cancel_task_after(:none)
    assert {:ok, auto_id} = TaskAfter.task_after(0, fn -> 42 end, send_result: self())
    assert_receive(42, 100)
    assert {:error, {:does_not_exist, ^auto_id}} = TaskAfter.cancel_task_after(auto_id)
  end

  test "TaskAfter and cancel but also run the callback in process (unsafe again)" do
    assert {:ok, auto_id} = TaskAfter.task_after(500, fn -> 42 end)
    assert {:ok, 42} = TaskAfter.cancel_task_after(auto_id, run_result: :in_process)
  end

  test "TaskAfter and cancel but also run the callback async" do
    s = self()
    assert {:ok, auto_id} = TaskAfter.task_after(500, fn -> send(s, 42) end)
    assert {:ok, :task} = TaskAfter.cancel_task_after(auto_id, run_result: :async)
    assert_receive(42, 600)
  end

  test "TaskAfter and cancel but also run the callback async while returning result to pid" do
    s = self()
    assert {:ok, auto_id} = TaskAfter.task_after(500, fn -> 42 end)
    assert {:ok, :task} = TaskAfter.cancel_task_after(auto_id, run_result: s)
    assert_receive(42, 600)
  end

  test "TaskAfter and crash" do
    s = self()
    len = &length/1
    d = len.([])
    assert {:ok, _auto_id0} = TaskAfter.task_after(100, fn -> send(s, 21) end)
    assert {:ok, _auto_id1} = TaskAfter.task_after(250, fn -> send(s, 1/d) end)
    assert {:ok, _auto_id2} = TaskAfter.task_after(500, fn -> send(s, 42) end)
    assert_receive(42, 600)
    assert_receive(21, 1)
    assert :no_message = (receive do m -> m after 1 -> :no_message end)
  end

  test "TaskAfter and replace callback without recreate" do
    assert {:ok, auto_id} = TaskAfter.task_after(500, fn -> 1 end, send_result: self())
    assert {:ok, ^auto_id} = TaskAfter.change_task_after(auto_id, callback: fn -> 2 end)
    assert_receive(2, 600)
    assert {:error, {:does_not_exist, ^auto_id}} = TaskAfter.change_task_after(auto_id, callback: fn -> 3 end)
  end

  test "TaskAfter and replace callback and timeout with recreate" do
    assert {:ok, auto_id} = TaskAfter.task_after(500, fn -> 1 end, send_result: self())
    assert {:ok, ^auto_id} = TaskAfter.change_task_after(auto_id, recreate_if_necessary: true, timeout_after_ms: 500, send_result: self(), callback: fn -> 2 end)
    assert_receive(2, 600)
    assert {:ok, ^auto_id} = TaskAfter.change_task_after(auto_id, recreate_if_necessary: true, timeout_after_ms: 500, send_result: self(), callback: fn -> 3 end)
    assert_receive(3, 600)
  end

  test "TaskAfter and replace callback without timeout with recreate" do
    assert {:ok, auto_id} = TaskAfter.task_after(500, fn -> 1 end, send_result: self())
    assert {:ok, ^auto_id} = TaskAfter.change_task_after(auto_id, recreate_if_necessary: true, timeout_after_ms: 500, send_result: self(), callback: fn -> 2 end)
    assert_receive(2, 600)
    assert {:ok, ^auto_id} = TaskAfter.change_task_after(auto_id, recreate_if_necessary: true, timeout_after_ms: {:default, 500}, send_result: self(), callback: fn -> 3 end)
    assert_receive(3, 600)
  end

  test "TaskAfter and replace timeout without recreate" do
    assert {:ok, auto_id} = TaskAfter.task_after(200, fn -> 1 end, send_result: self())
    assert {:ok, ^auto_id} = TaskAfter.change_task_after(auto_id, timeout_after_ms: 500)
    assert :no_message = (receive do m -> m after 300 -> :no_message end)
    assert_receive(1, 600)
  end