Question reg. durable duplex and parallelism in workflow foundation 4

I've two workflows hosted as services and from workflow-1 I'm invoking the other one workflow-2 through durable duplex. The workflow-1 sends two requests two workflow-2 creating two instances and keeps on running. When workflow-2 instances done with their job they call back the same workflow-1 instance that is running through correlation. My question is what happens if the two workflow-2 instances in开发者_JS百科voke the workflow-1 at the same time. Will the calls executed one by one in a queue fashion or they get executed in different threads at the same time?

There is no multi threaded execution of a single workflow instance. The second call will be scheduled when it is received and start processing as soon as the scheduler gets to is.