Add Flow.child_spec/1

Author: josevalim

lib/flow.ex

@@ -307,25 +307,38 @@ defmodule Flow do
 
   Flow allows computations to be started as a group of processes
   which may run indefinitely. This can be done by starting
-  the flow as part of a supervision tree using `Flow.start_link/2`.
-
-  Since Elixir v1.5, the easiest way to add Flow to your supervision
-  tree is by calling `use Flow` and then defining a `start_link/1`.
+  the flow as part of a supervision tree using `{Flow, your_flow}`
+  as your child specification:
+
+      children = [
+        {Flow,
+         Flow.from_stages(...)
+         |> Flow.flat_map(&String.split(&1, " "))
+         |> Flow.reduce(fn -> %{} end, fn word, acc ->
+           Map.update(acc, word, 1, & &1 + 1)
+         end)}
+      ]
+
+  It is also possible to move a Flow to its own module. This is done by
+  calling `use Flow` and then defining a `start_link/1` function that
+  calls `Flow.start_link/1` at the end:
 
       defmodule MyFlow do
         use Flow
 
         def start_link(_) do
           Flow.from_stages(...)
-          |> ...
-          |> ...
-          |> ...
+          |> Flow.flat_map(&String.split(&1, " "))
+          |> Flow.reduce(fn -> %{} end, fn word, acc ->
+            Map.update(acc, word, 1, & &1 + 1)
+          end)
           |> Flow.start_link()
         end
       end
 
-  The `:shutdown` and `:restart` child spec configurations can be
-  given to `use Flow`.
+  By the default the `Flow` is permanent, which means it is always
+  restarted. The `:shutdown` and `:restart` child spec configurations
+  can be given to `use Flow`.
 
   Flow also provides integration with `GenStage`, allowing you to
   specify child specifications of producers, producer consumers, and
@@ -494,6 +507,14 @@ defmodule Flow do
     end
   end
 
+  @doc false
+  def child_spec(%Flow{} = arg) do
+    %{
+      id: __MODULE__,
+      start: {__MODULE__, :start_link, [arg]}
+    }
+  end
+
   ## Building
 
   @doc """

test/flow_test.exs

@@ -99,6 +99,22 @@ defmodule FlowTest do
     end
   end
 
+  test "child_spec/2" do
+    parent = self()
+
+    start_supervised!(
+      {Flow,
+       Flow.from_enumerables([[1, 2, 3], [4, 5, 6]], stages: 2)
+       |> Flow.filter(&(rem(&1, 2) == 0))
+       |> Flow.map(&send(parent, &1))}
+    )
+
+    assert_receive 2
+    assert_receive 4
+    assert_receive 6
+    refute_received 1
+  end
+
   describe "errors" do
     test "on multiple reduce calls" do
       message = ~r"cannot call group_by/reduce/emit_and_reduce on a flow after another"
@@ -777,8 +793,8 @@ defmodule FlowTest do
       assert_receive {:consumed, [2]}
       assert_receive {:consumed, [4]}
       assert_receive {:consumed, [6]}
-      assert_receive {:consumed, '\b'}
-      assert_receive {:consumed, '\n'}
+      assert_receive {:consumed, [8]}
+      assert_receive {:consumed, [10]}
     end
 
     test "into_stages/3 with :name", config do
@@ -805,19 +821,19 @@ defmodule FlowTest do
 
       assert_receive {:producer_consumed, [2]}
       assert_receive {:producer_consumed, [6]}
-      assert_receive {:producer_consumed, '\b'}
+      assert_receive {:producer_consumed, [8]}
       assert_receive {:producer_consumed, [1]}
       assert_receive {:producer_consumed, [5]}
-      assert_receive {:producer_consumed, '\a\t'}
+      assert_receive {:producer_consumed, ~c"\a\t"}
       assert_receive {:producer_consumed, [3]}
       assert_receive {:producer_consumed, [4]}
-      assert_receive {:producer_consumed, '\n'}
+      assert_receive {:producer_consumed, [10]}
 
       assert_receive {:producer_consumed, [2]}
       assert_receive {:producer_consumed, [6]}
-      assert_receive {:producer_consumed, '\b'}
+      assert_receive {:producer_consumed, [8]}
       assert_receive {:producer_consumed, [4]}
-      assert_receive {:producer_consumed, '\n'}
+      assert_receive {:producer_consumed, [10]}
     end
 
     test "through_stages/3 + into_stages/3" do
@@ -833,25 +849,25 @@ defmodule FlowTest do
 
       assert_receive {:producer_consumed, [2]}
       assert_receive {:producer_consumed, [6]}
-      assert_receive {:producer_consumed, '\b'}
+      assert_receive {:producer_consumed, [8]}
       assert_receive {:producer_consumed, [1]}
       assert_receive {:producer_consumed, [5]}
-      assert_receive {:producer_consumed, '\a\t'}
+      assert_receive {:producer_consumed, ~c"\a\t"}
       assert_receive {:producer_consumed, [3]}
       assert_receive {:producer_consumed, [4]}
-      assert_receive {:producer_consumed, '\n'}
+      assert_receive {:producer_consumed, [10]}
 
       assert_receive {:producer_consumed, [2]}
       assert_receive {:producer_consumed, [6]}
-      assert_receive {:producer_consumed, '\b'}
+      assert_receive {:producer_consumed, [8]}
       assert_receive {:producer_consumed, [4]}
-      assert_receive {:producer_consumed, '\n'}
+      assert_receive {:producer_consumed, [10]}
 
       assert_receive {:consumed, [2]}
       assert_receive {:consumed, [6]}
-      assert_receive {:consumed, '\b'}
+      assert_receive {:consumed, [8]}
       assert_receive {:consumed, [4]}
-      assert_receive {:consumed, '\n'}
+      assert_receive {:consumed, [10]}
     end
 
     test "into_specs/3" do
@@ -863,8 +879,8 @@ defmodule FlowTest do
       assert_receive {:consumed, [2]}
       assert_receive {:consumed, [4]}
       assert_receive {:consumed, [6]}
-      assert_receive {:consumed, '\b'}
-      assert_receive {:consumed, '\n'}
+      assert_receive {:consumed, [8]}
+      assert_receive {:consumed, [10]}
     end
 
     test "into_specs/3 with :name", config do
@@ -886,19 +902,19 @@ defmodule FlowTest do
 
       assert_receive {:producer_consumed, [2]}
       assert_receive {:producer_consumed, [6]}
-      assert_receive {:producer_consumed, '\b'}
+      assert_receive {:producer_consumed, [8]}
       assert_receive {:producer_consumed, [1]}
       assert_receive {:producer_consumed, [5]}
-      assert_receive {:producer_consumed, '\a\t'}
+      assert_receive {:producer_consumed, ~c"\a\t"}
       assert_receive {:producer_consumed, [3]}
       assert_receive {:producer_consumed, [4]}
-      assert_receive {:producer_consumed, '\n'}
+      assert_receive {:producer_consumed, [10]}
 
       assert_receive {:producer_consumed, [2]}
       assert_receive {:producer_consumed, [6]}
-      assert_receive {:producer_consumed, '\b'}
+      assert_receive {:producer_consumed, [8]}
       assert_receive {:producer_consumed, [4]}
-      assert_receive {:producer_consumed, '\n'}
+      assert_receive {:producer_consumed, [10]}
     end
 
     test "through_specs/3 + into_specs/3" do
@@ -910,25 +926,25 @@ defmodule FlowTest do
 
       assert_receive {:producer_consumed, [2]}
       assert_receive {:producer_consumed, [6]}
-      assert_receive {:producer_consumed, '\b'}
+      assert_receive {:producer_consumed, [8]}
       assert_receive {:producer_consumed, [1]}
       assert_receive {:producer_consumed, [5]}
-      assert_receive {:producer_consumed, '\a\t'}
+      assert_receive {:producer_consumed, ~c"\a\t"}
       assert_receive {:producer_consumed, [3]}
       assert_receive {:producer_consumed, [4]}
-      assert_receive {:producer_consumed, '\n'}
+      assert_receive {:producer_consumed, [10]}
 
       assert_receive {:producer_consumed, [2]}
       assert_receive {:producer_consumed, [6]}
-      assert_receive {:producer_consumed, '\b'}
+      assert_receive {:producer_consumed, [8]}
       assert_receive {:producer_consumed, [4]}
-      assert_receive {:producer_consumed, '\n'}
+      assert_receive {:producer_consumed, [10]}
 
       assert_receive {:consumed, [2]}
       assert_receive {:consumed, [6]}
-      assert_receive {:consumed, '\b'}
+      assert_receive {:consumed, [8]}
       assert_receive {:consumed, [4]}
-      assert_receive {:consumed, '\n'}
+      assert_receive {:consumed, [10]}
     end
   end