Enable graceful shutdown of a GenConsumer

Add a user-configurable :shutdown to GenConsumer's child_spec.

Addresses #434.

lib/kafka_ex/gen_consumer.ex

@@ -209,6 +209,7 @@ defmodule KafkaEx.GenConsumer do
  | {:commit_threshold, non_neg_integer}
  | {:auto_offset_reset, :none | :earliest | :latest}
  | {:api_versions, map()}
+ | {:shutdown, timeout()}
  | {:extra_consumer_args, map()}
 
  @typedoc """
@@ -438,6 +439,8 @@ defmodule KafkaEx.GenConsumer do
  * `:fetch_options` - Optional keyword list that is passed along to the
  `KafkaEx.fetch` call.
 
+ * `:shutdown` - Optional amount of time in milliseconds that the supervisor will wait for a `GenConsumer` to terminate after emitting a `Process.exit(child, :shutdown)` signal. Defaults to `5_000`.
+
  * `:extra_consumer_args` - Optional parameter that is passed along to the
  `GenConsumer.init` call in the consumer module. Note that if `init/3` is not
  implemented, the default implementation calls to `init/2`, dropping the extra

lib/kafka_ex/gen_consumer/supervisor.ex

@@ -15,6 +15,8 @@ defmodule KafkaEx.GenConsumer.Supervisor do
 
  use DynamicSupervisor
 
+ @default_worker_shutdown 5_000
+
  @doc """
  Starts a `GenConsumer.Supervisor` process linked to the current process.
 
@@ -57,7 +59,8 @@ defmodule KafkaEx.GenConsumer.Supervisor do
  id: gen_consumer_module,
  start:
  {gen_consumer_module, :start_link,
- [consumer_module, group_name, topic, partition, opts]}
+ [consumer_module, group_name, topic, partition, opts]},
+ shutdown: Keyword.get(opts, :shutdown, @default_worker_shutdown)
  }
  end