How to Avoid Race Conditions in Rails

When two users read and update a database record at the same time, you might run into critical problems that are undesirable. Let's say that for some reason, a customer clicks the pay button on the checkout page of an e-commerce website. It is possible to have a scenario where a particular customer is charged twice for the same order because the two requests to charge the order were made at almost the same time. This situation is called a "race condition."A race condition occurs when two or more threads can access shared data and try to change it at the same time. Because the thread scheduling algorithm can swap between threads at any time, you don't know the order in which the threads will attempt to access the shared data. Therefore, the result of the data change is dependent on the thread scheduling algorithm (i.e., both threads are "racing" to access/change the data). Problems often occur when one thread does a "check-then-act" (e.g., "Check" if the value is X, and then "act" to do something that depends on the value being X) and another thread does something to the value in between the "check" and the "act" processes. —Stack Overflow.