Merge pull request #1169 from andrewhr/async-middleware-telemetry

Add telemetry events to async middleware

lib/absinthe/middleware/async.ex

@@ -50,8 +50,14 @@ defmodule Absinthe.Middleware.Async do
   # This function inserts additional middleware into the remaining middleware
   # stack for this field. On the next resolution pass, we need to `Task.await` the
   # task so we have actual data. Thus, we prepend this module to the middleware stack.
-  def call(%{state: :unresolved} = res, {fun, opts}) when is_function(fun),
-    do: call(res, {Task.async(fun), opts})
+  def call(%{state: :unresolved} = res, {fun, opts}) when is_function(fun) do
+    task =
+      Task.async(fn ->
+        :telemetry.span([:absinthe, :middleware, :async, :task], %{}, fn -> {fun.(), %{}} end)
+      end)
+
+    call(res, {task, opts})
+  end
 
   def call(%{state: :unresolved} = res, {task, opts}) do
     task_data = {task, opts}

test/absinthe/middleware/async_test.exs

@@ -75,12 +75,39 @@ defmodule Absinthe.Middleware.AsyncTest do
     assert {:ok, %{data: %{"asyncBareThing" => "bare task"}}} == Absinthe.run(doc, Schema)
   end
 
-  test "can resolve a field using the normal test helper" do
+  test "can resolve a field using the normal test helper and emit telemetry event", %{test: test} do
     doc = """
     {asyncThing}
     """
 
+    pid = self()
+
+    :ok =
+      :telemetry.attach_many(
+        "#{test}",
+        [
+          [:absinthe, :middleware, :async, :task, :start],
+          [:absinthe, :middleware, :async, :task, :stop]
+        ],
+        fn name, measurements, metadata, _config ->
+          send(pid, {:telemetry_event, name, measurements, metadata})
+        end,
+        _config = %{}
+      )
+
     assert {:ok, %{data: %{"asyncThing" => "we async now"}}} == Absinthe.run(doc, Schema)
+
+    assert_receive {:telemetry_event, [:absinthe, :middleware, :async, :task, :start],
+                    %{system_time: _}, %{}}
+
+    assert_receive {:telemetry_event, [:absinthe, :middleware, :async, :task, :stop],
+                    %{duration: _}, %{}}
+
+    assert_receive {:telemetry_event, [:absinthe, :middleware, :async, :task, :start],
+                    %{system_time: _}, %{}}
+
+    assert_receive {:telemetry_event, [:absinthe, :middleware, :async, :task, :stop],
+                    %{duration: _}, %{}}
   end
 
   test "can resolve a field using a cooler but probably confusing to some people helper" do