AndrewKlymchuk

AndrewKlymchuk

Hello,
I’ve encountered a problem when using Task.async_stream/3 within tests where sandbox shared mode is enabled.

I have the following test:

defmodule MyApp.SharedModeTest do
  use MyApp.DataCase, async: false

  test "shared mode works" do
      MyApp.Repo.transaction(fn ->
        Task.async_stream(
          [1],
          fn id -> MyApp.Repo.get(MySchema, id) end,
          timeout: :infinity
        )
        |> Enum.to_list()
      end)
  end
end

DataCase content looks as follow:

  setup tags do
    :ok = Sandbox.checkout(MyApp.Repo)

    unless tags[:async] do
      Sandbox.mode(MyApp.Repo, {:shared, self()})
    end

    :ok
  end

It fails with the following exception:

** (EXIT from #PID<0.3878.0>) exited in: DBConnection.Holder.checkout(#PID<0.3879.0>, [log: #Function<13.86356856/1 in Ecto.Adapters.SQL.with_log/3>, source: "my_table", cast_params: [1], repo: MyApp.Repo, timeout: 15000, pool_size: 10, pool: DBConnection.Ownership, ownership_timeout: 600000, queue_target: 600000, queue_interval: 600000])
         ** (EXIT) shutdown: %DBConnection.ConnectionError{message: "client #PID<0.3878.0> timed out because it queued and checked out the connection for longer than 15000ms\n\nClient #PID<0.3878.0> is still using a connection from owner at location:\n\n    (elixir 1.17.1) lib/task/supervised.ex:292: Task.Supervised.stream_reduce/7\n    (elixir 1.17.1) lib/enum.ex:4423: Enum.reverse/1\n    (elixir 1.17.1) lib/enum.ex:3748: Enum.to_list/1\n    (ecto_sql 3.11.3) lib/ecto/adapters/sql.ex:1358: anonymous fn/3 in Ecto.Adapters.SQL.checkout_or_transaction/4\n    (db_connection 2.6.0) lib/db_connection.ex:1710: DBConnection.run_transaction/4\n    ...

Apparently, db connection isn’t shared with task process, therefore it tries to check it out, but fails because it is already checked out by test process.
If I remove transaction from the test, it works as expected:

defmodule MyApp.SharedModeTest do
  use MyApp.DataCase, async: false

  test "shared mode works" do
      Task.async_stream(
        [1],
        fn id -> MyApp.Repo.get(MySchema, id) end,
        timeout: :infinity
      )
      |> Enum.to_list()
  end
end

My perception is that transaction must not affect db connection sharing among processes.
Is it a bug, or I misunderstand how it must work?

Where Next? Top

Trending in Questions Top

RSP87
I’m working on a project that simulates the bumbl example in the programming phoenix book. It acts almost like an email client. We have a...
New
nseaSeb
Hello, I know there is an approach for handling lists that allows for optimized traversal, but I can’t recall the specific method (somet...
New
brecabral
Documentation While reading the Scoped Routes section, I noticed that the documentation currently refers to a problem without explainin...
New
kpanic
Hi everyone, I am toying with the idea of building a “match maker” for giving personal help to people that wants to start coding. I sta...
New
velrest
So my question is quite simple and i have found no conclusive answer on forum, google or AI. Should we use :erlang.float for Integer to ...
New
asweet-confluent
I recently noticed that Elixir’s Logger defaults its primary log level to :debug when no :logger, :level application configuration is pre...
New
apz
I’m new to elixir and just tried to install the elixirLS extension for VScode(ium) and it is throwing some errors that I would like help ...
New

Other Trending Topics Top

GenericJam
Edit: 2026 May 15 - This post is archived. Mob is alive!! Main docs: mob v0.7.11 — Documentation A bit of explanation for the slightly c...
New
JesseHerrick
Hey, I’m Jesse and I’m the main contributor behind Dexter, a full-featured, lightning-fast Elixir LSP optimized for large codebases. It s...
New
mudasobwa
I am happy to introduce the very α version of the new programming language compiled to BEAM. Welcome Cure. It has literally three kille...
New
garrison
Hobbes is a low-level distributed database for the Elixir programming language. Hobbes provides a simple, safe, and scalable storage lay...
New
marciok
Hi there! We created Gust: A task orchestrator inspired by Airflow. For those who have never heard about Aiflow, it’s a Python-based wor...
New
mhanberg
Hi everyone! The first release candidate for the Expert language server project is now available! We’ve published a press release detai...
New

We're in Beta

About us Mission Statement

Options

Thread Display Mode




Thread Preview

Skip Thread Previews