Timerfd

timerfd Counts Expirations Through Descriptor I/O

A periodic timerfd does not require one userspace wakeup for every timer expiration. If several expirations occur before the descriptor is read, Linux accumulates them and returns the count in one 8-byte integer. That behavior makes timer state fit the same readiness model used for sockets, pipes, and other descriptors. It also gives delayed event loops explicit information about missed periods rather than collapsing several expirations into one notification. Expiration state becomes readable descriptor data timerfd_create() creates a timer object and returns a file descriptor referring to it. The selected clock defines the timer’s time base. Common choices include CLOCK_MONOTONIC, CLOCK_REALTIME, and CLOCK_BOOTTIME.