add documentation

lib/exq/dequeue/behaviour.ex

@@ -1,5 +1,38 @@
 defmodule Exq.Dequeue.Behaviour do
-  @callback init(info :: map, args :: term) :: {:ok, term}
+  @moduledoc """
+  Custom concurreny or rate limiting at a queue level can be achieved
+  by implementing the Dequeue behaviour
+
+  The following config can be used to customize dequeue behaviour for a queue
+
+      config :exq,
+        queues: [{"default", {RateLimiter, options}}]
+
+  RateLimiter module should implement `Exq.Dequeue.Behaviour`. The
+  options supplied here would be passed as the second argument to the
+  `c:init/2` function.
+
+  ### Life cycle
+
+  `c:init/2` will be invoked on initialization. The first argument will contain info
+  like queue and the second argument is user configurable.
+
+  `c:available?/1` will be invoked before each poll. If the
+  returned value contains `false` as the second element of the tuple,
+  the queue will not polled
+
+  `c:dispatched/1` will be invoked once a job is dispatched to the worker
+
+  `c:processed/1` will be invoked if a job completed successfully
+
+  `c:failed/1` will be invoked if a job failed
+
+  `c:stop/1` will be invoked when a queue is unsubscribed or before the
+  node terminates. Note: there is no guarantee this will be invoked if
+  the node terminates abruptly
+  """
+
+  @callback init(info :: %{queue: String.t()}, args :: term) :: {:ok, term}
   @callback stop(state :: term) :: :ok
   @callback available?(state :: term) :: {:ok, boolean, term}
   @callback dispatched(state :: term) :: {:ok, term}

lib/exq/dequeue/local.ex

@@ -2,6 +2,8 @@ defmodule Exq.Dequeue.Local do
   @behaviour Exq.Dequeue.Behaviour
 
   defmodule State do
+    @moduledoc false
+
     defstruct max: nil, current: 0
   end