But that is still not asynchronous in relation to the program flow. Running other unrelated tasks is not asynchronous like that, it's concurrent execution. Asynchronous would mean that something that share context, time or execution, is run out of order in relation to each other. And even if it's using optimistic concurrent execution, in relation to program flow it's still synchronous. The event loop is still synchronizing program flow, even if it does optimistic concurrency control. Concurrent doesn't mean "out of order", it means "at the same time".