[amelius]

Another consideration: often you want to wait for several types of object (timer, semaphore, file, etc.), so you need one interface where you can do wait([A, B, C, ...]) where A can be a timer and B a semaphore, C a file, etc. Basically, the OS should present a unified interface.

[chikere232]

Often such apis (select/poll/epoll) have an option to wait with a timeout, so if you have a bunch of different timers, you can manage them yourself (e.g. on a heap) and set the timeout to the nearest timer

Of course if you have epoll you probably have timerfd, wich does give you a unified interface, just not as portable