fix exchange deletion logic

It seems deletion requests come duplicated, worth asking RabbitMQ if
it's intended behaviour.

Signed-off-by: Matteo Cafasso <[email protected]>

Author: noxdafox

lib/cache.ex

@@ -49,6 +49,13 @@ defmodule RabbitMQ.Cache do
     GenServer.call(cache, {:drop, cache})
   end
 
+  @doc """
+  Return the PID of the given cache, nil if non existing.
+  """
+  def process(cache) do
+    GenServer.whereis(cache)
+  end
+
   ## Server Callbacks
 
   def init({cache, options}) do
@@ -97,7 +104,10 @@ defmodule RabbitMQ.Cache do
   end
 
   def handle_call({:drop, cache}, _from, state) do
-    {:reply, Mnesia.delete_table(cache), state}
+    case Mnesia.delete_table(cache) do
+      {:atomic, :ok} -> {:reply, :ok, state}
+      _ -> {:reply, :error, state}
+    end
   end
 
   ## Utility functions

lib/rabbit_message_deduplication_exchange.ex

@@ -112,8 +112,13 @@ defmodule RabbitMQ.ExchangeTypeMessageDeduplication do
   def delete(_tx, exchange(name: name), _bs) do
     cache = cache_name(name)
 
-    {_, :ok} = RabbitMQ.Cache.drop(cache)
-    :ok = RabbitMQ.Supervisor.terminate_child(cache)
+    # It seems the deletion request comes duplicated
+    case RabbitMQ.Cache.process(cache) do
+      pid when is_pid(pid) ->
+        :ok = RabbitMQ.Cache.drop(cache)
+        RabbitMQ.Supervisor.terminate_child(pid)
+      nil -> :ok
+    end
   end
 
   def policy_changed(_x1, _x2) do