Concurrent Data Processing in Elixir TIL Series: Task.async_stream/3

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Concurrent Data Processing in Elixir TIL Series: Task.async_stream/3

Pau Riosa's photo
Pau Riosa
ยทDec 31, 2021ยท

1 min read

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Task.async_stream/3

  • returns a Stream (Streams in Elixir are data structures that hold one or more operations that don't run immediately, only when explicitly told so) sometimes called lazy enumerables
  • will start a process and run the function
  • works just like Enum.map/2 and Task.async/2 combined
  • You can set a limit on the number of processes running at the same time via max_concurrency option.
  • make sure to follow up a call of Enum to process the function

Options

  • max_concurrency - good for setting the maximum number of task to run at the same time.
  • on_timeout - When a task reaches a timeout, it will produce an exception, stopping the stream and crashing the current process. This is useful for managing one process at a time. You can choose either exit or kill_task.
  • ordered is useful if you do not want to idle processes if one task is taking longer.

Example


defmodule MyApp.Sender do
  def send_email(email) do
    ...
  end

  def notify_all(emails) do
    emails
    |> Task.async_stream(&send_email/1, on_timeout: :kill_task, ordered: false, max_concurrency: 1)
    |> Enum.to_list()
  end

  ...
end

iex> Sender.notify_all(emails)
Email to hello@world.com sent.
Email to hola@world.com sent.
Email to nihao@world.com sent.
Email to konnichiwa@world.com sent.
[
  ok: {:ok, "email_sent"},
  ok: {:ok, "email_sent"},
  ok: {:ok, "email_sent"},
  ok: {:ok, "email_sent"}
]
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