FIX: DistributedMutex (#7953)

spec/components/distributed_mutex_spec.rb

@@ -98,4 +98,47 @@ describe DistributedMutex do
     end
   end
 
+  context "executions" do
+    it "should not allow critical sections to overlap" do
+      connections = (0...3).map { DiscourseRedis.new }
+
+      scenario =
+        Concurrency::Scenario.new do |execution|
+          locked = false
+
+          $redis.del('mutex_key')
+
+          connections.each do |connection|
+            connection.unwatch
+          end
+
+          3.times do |i|
+            execution.spawn do
+              begin
+                redis =
+                  Concurrency::RedisWrapper.new(
+                    connections[i],
+                    execution
+                  )
+
+                2.times do
+                  DistributedMutex.synchronize('mutex_key', redis: redis) do
+                    raise "already locked #{execution.path}" if locked
+                    locked = true
+
+                    execution.yield
+
+                    raise "already unlocked #{execution.path}" unless locked
+                    locked = false
+                  end
+                end
+              rescue Redis::ConnectionError
+              end
+            end
+          end
+        end
+
+      scenario.run(runs: 10)
+    end
+  end
 end