Industrial fault description:

F1 is a fault that occurs in using asynchronous tasks in a single request, when we send messages asynchronously without message sequence control.
Suppose we have Event A and Event B in a request, while Event A always processes and returns earlier than Event B.
But sometimes, due to some specific reasons, Event A processes and returns later than Event B.
Then F1 will occur.



TrainTicket replicated fault description:

In ticket-cancellation logic of the TrainTicket system, we have two major events: [Drawback Money] and [Reset Order Status].
If the user decided to cancel an order, the Ticket-Cancel-Service firstly call Inside-Payment-Service to drawback money.
Then Inside-Payment-Service call Order-Service to set the order status to CANCELLING. 
Then the system refunds the money to user.
After that, the Cancel-Service call Order-Service set the order status to CANCEL. 
Then the whole cancel process is done.
In our fault reproduction, we made a random delay in event [Drawback Money] to simulate the situation of network congestion.
In this case, the event [Reset Order Stauts] will complete before [Drawback Money], then the fault occurs.