# Using System.stacktrace() within exq middleware behaviour implementation

**URL:** <https://forum.elixirforum.com/t/using-system-stacktrace-within-exq-middleware-behaviour-implementation/15813>\
**Category:** Questions\
**Tags:** exq, appsignal\
**Created:** [August 13, 2018, 5:52pm UTC](https://forum.elixirforum.com/t/using-system-stacktrace-within-exq-middleware-behaviour-implementation/15813 "2018-08-13T17:52:52Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![tetiana](https://forum.elixirforum.com/user_avatar/forum.elixirforum.com/tetiana/32/8272_2.png) [@tetiana](https://forum.elixirforum.com/u/tetiana)\
**Post date:** [August 13, 2018, 5:52pm UTC](https://forum.elixirforum.com/t/using-system-stacktrace-within-exq-middleware-behaviour-implementation/15813/1 "2018-08-13T17:52:53Z")

</div>

Before Elixir 1.7 we were happy to send errors to appsignal when exq job failed to complete.  
We have implemented a middleware behaviour to achieve that.

```elixir
defmodule Exq.Middleware.AppSignal do
  @moduledoc false

  @behaviour Exq.Middleware.Behaviour

  alias Exq.Middleware.Pipeline
  import Pipeline

  def before_work(pipeline) do
    transaction =
      Appsignal.Transaction.generate_id()
      |> Appsignal.Transaction.start(:background_job)
      |> Appsignal.Transaction.set_action("Exq/#{pipeline.assigns.worker_module}")
      |> Appsignal.Transaction.set_sample_data(
        "environment",
        %{job_id: pipeline.assigns.job.jid}
      )

    assign(pipeline, :appsignal_transaction, transaction)
  end

  def after_processed_work(pipeline) do
    transaction = pipeline.assigns.appsignal_transaction
    Appsignal.Transaction.finish(transaction)
    Appsignal.Transaction.complete(transaction)

    pipeline
  end

  def after_failed_work(pipeline) do
    transaction = pipeline.assigns.appsignal_transaction

    _ =
      Appsignal.Transaction.set_error(
        transaction,
        "Exq job failed with exception",
        pipeline.assigns.error_message,
        System.stacktrace() # <---- DEPRECATED!
      )

    Appsignal.Transaction.finish(transaction)
    Appsignal.Transaction.complete(transaction)

    pipeline
  end
end

```

In Elixir 1.7.2 `System.stacktrace()` is deprecated, so we are wondering what would be the best way to report errors to appsignal from our middleware.

We can pass stacktrace as `[]`. That is not ideal, as it would be great to have stacktrace.

As compilation warning suggests, use ` __STACKTRACE__ ` in try/rescue block and once we have stacktrace pass it to `after_failed_work` callback as second parameter? But that would mean that we have to suggest to change `Exq.Middleware.Behaviour` definition to allow optional stacktrace argument.

If you have an idea of how we can solve this, don’t hesitate to share and discuss.

---

<div class="post-metadata">

**Author:** ![OvermindDL1](https://forum.elixirforum.com/user_avatar/forum.elixirforum.com/overminddl1/32/2677_2.png) [@OvermindDL1](https://forum.elixirforum.com/u/OvermindDL1)\
**Post date:** [August 13, 2018, 10:28pm UTC](https://forum.elixirforum.com/t/using-system-stacktrace-within-exq-middleware-behaviour-implementation/15813/2 "2018-08-13T22:28:47Z")

</div>

Ugly and slow, but you could maybe ‘make’ your own stacktrace? by just raising and catching your own error? Though getting a stacktrace in the old versions was not fast either so eh. ^.^;

---

<div class="post-metadata">

**Author:** ![tetiana](https://forum.elixirforum.com/user_avatar/forum.elixirforum.com/tetiana/32/8272_2.png) [@tetiana](https://forum.elixirforum.com/u/tetiana)\
**Post date:** [August 15, 2018, 8:18am UTC](https://forum.elixirforum.com/t/using-system-stacktrace-within-exq-middleware-behaviour-implementation/15813/3 "2018-08-15T08:18:12Z")

</div>

Yeah. That’s an interesting idea. I’ll keep it in mind. Also, I will dive into exq library to see if stack trace can be passed to the `after_processed_work`.

---

<div class="post-metadata">

**Author:** ![dideler](https://forum.elixirforum.com/user_avatar/forum.elixirforum.com/dideler/32/9953_2.png) [@dideler](https://forum.elixirforum.com/u/dideler)\
**Post date:** [September 7, 2018, 5:00pm UTC](https://forum.elixirforum.com/t/using-system-stacktrace-within-exq-middleware-behaviour-implementation/15813/4 "2018-09-07T17:00:17Z")

</div>

We have the same issue, that is, using `System.stacktrace/0` without an exception and therefore no rescue/catch.

We have some code where we handle error tuples by collecting information, which includes the stacktrace, and send the data to a monitoring service.

```elixir
def set_error(transaction, name, message, reason) do backtrace = ([reason] ++ 
  System.stacktrace()) |&gt; Enum.map(&amp;inspect/1) 
  Appsignal.Transaction.set_error(transaction, name, message, backtrace)
end

```

I’ve considered creating our own fake exception but that changes the stacktrace.