Fix race condition in unique job lookup, #87

lib/sidekiq/middleware/client/unique_jobs.rb

@@ -9,13 +9,23 @@ module Sidekiq
 
         def call(item, queue)
           payload_hash = Digest::MD5.hexdigest(MultiJson.encode(item))
+          unique = false
+
           Sidekiq.redis do |conn|
-            return if conn.get(payload_hash)
-            conn.setex(payload_hash, HASH_KEY_EXPIRATION, 1)
+            conn.watch(payload_hash)
+
+            if conn.get(payload_hash)
+              conn.unwatch
+            else
+              unique = conn.multi do
+                conn.setex(payload_hash, HASH_KEY_EXPIRATION, 1)
+              end
+            end
           end
 
-          yield
+          yield if unique
         end
+
       end
     end
   end

test/test_client.rb

@@ -28,17 +28,19 @@ class TestClient < MiniTest::Unit::TestCase
   describe 'with mock redis' do
     before do
       @redis = MiniTest::Mock.new
-      def @redis.multi; yield; end
+      def @redis.multi; yield if block_given?; end
       def @redis.set(*); true; end
       def @redis.sadd(*); true; end
       def @redis.srem(*); true; end
       def @redis.get(*); nil; end
       def @redis.del(*); nil; end
       def @redis.incrby(*); nil; end
-      def @redis.setex(*); nil; end
+      def @redis.setex(*); true; end
       def @redis.expire(*); true; end
+      def @redis.watch(*); true; end
       def @redis.with_connection; yield self; end
       def @redis.with; yield self; end
+      def @redis.exec; true; end
       Sidekiq.instance_variable_set(:@redis, @redis)
     end