The whole process took more than a month. The first two rounds happened within one week. The next two rounds went through numerous reschedulings and eventually happened more than a month later. I received a rejection a day after the last round, which was surprisingly faster than the rest of the process. I did fairly well in the interviews.

Implement a worker and a multiworker class. Works get added to a multiworker object and are executed till completion. All work completion generates a common callback.