7.7.1 Introduction to the timerfd API

The timerfd API allows the definition of time–periodic events by specification of two time intervals:

1. Initial expiration: how much time before the first event.
2. Period: how much time between two time–adjacent events.

    time before the
    first event       period      period      period
   |               |           |           |           |
---+---------------+-----------+-----------+-----------+----
   ^               ^           ^           ^           ^
  now          1st event   2nd event   3rd event   4th event

Each timer can be started, stopped, reconfigured and queried for how much time until the next event.