> ## Documentation Index
> Fetch the complete documentation index at: https://docs.appsignal.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Mix tasks

AppSignal for Elixir doesn't automatically instrument mix tasks, but you can set up manual instrumentation and error handling using [custom instrumentation](/elixir/instrumentation/).

## Starting and stopping AppSignal

Since Mix tasks don't automatically start applications, you'll need to explicitly start the `:appsignal` application in your task:

<CodeGroup>
  ```elixir Elixir theme={null}
  Application.ensure_all_started(:appsignal)
  ```
</CodeGroup>

To make sure AppSignal has enough time to flush data to its agent, call `Appsignal.Nif.stop/0` at the end of your task, which blocks until the extension has had enough time to flush the sent payloads to the agent before stopping.

## Catching errors

To wrap errors in your task to be sent to AppSignal, add a `rescue` block to catch errors from your code. Pass the captured exception to `Appsignal.send_error/3` to report it to AppSignal. Add an `after` clause to your `rescue` block to call `Appsignal.Nif.stop/0`.

<CodeGroup>
  ```elixir Elixir theme={null}
  defmodule Mix.Tasks.Rescue do
    use Mix.Task

    def run(_) do
      {:ok, _} = Application.ensure_all_started(:appsignal)

      raise "rescue!"
    catch
      kind, reason ->
        stack = __STACKTRACE__
        Appsignal.send_error(kind, reason, stack)
        reraise(reason, stack)
    after
      Appsignal.Nif.stop
      :timer.sleep(35_000) # For one-off containers
    end
  end
  ```
</CodeGroup>

**Note:** A sleep of 35 seconds was added to the end of the Mix task. This is recommended for tasks that are run on one-off containers. When the task completes the process stops. The `Appsignal.Nif.stop/0` function call flushes all the transaction data currently in the AppSignal extension to our agent. There it is [transmitted on a 30 second interval](/appsignal/how-appsignal-operates#agent). The one-off container may have exited before that time. To ensure the data is still transmitted, it needs to wait for 35 seconds.

## Measuring performance

To measure performance in your task, start and stop a transaction manually and add events using the instrumentation helpers, like described in the [custom helper instrumentation](/elixir/instrumentation/instrumentation#helper-transactions).

<CodeGroup>
  ```elixir Elixir theme={null}
  defmodule Mix.Tasks.Instrument do
    use Mix.Task

    def run(_) do
      {:ok, _} = Application.ensure_all_started(:appsignal)

      Appsignal.instrument(fn span ->
        span
        |> Appsignal.Span.set_namespace("background_job")
        |> Appsignal.Span.set_name("Mix.Tasks.Instrument")

        Appsignal.instrument(fn span ->
          Appsignal.Span.set_name("task.instrumented")
          :timer.sleep(1_000)
        end)
      end)

      Appsignal.Nif.stop()
      :timer.sleep(35_000) # For one-off containers
    end
  end
  ```
</CodeGroup>