timerfdcreate

timerfd_create is a Linux system call that creates a new timer file descriptor. This file descriptor can be used to wait for timer events. It is a way to receive timer expirations as readable events on a file descriptor, similar to how one might read from a pipe or socket.

The function takes two arguments: a clock ID and flags. The clock ID specifies the type of clock to use for the timer. Common clock IDs include CLOCK_REALTIME (system-wide real-time clock) and CLOCK_MONOTONIC (a clock that cannot be set backward). The flags argument controls the behavior of the timerfd. For example, TFD_NONBLOCK makes the file descriptor non-blocking, meaning read operations will not wait if no data is available. TFD_CLOEXEC sets the close-on-exec flag for the file descriptor.

Once a timerfd is created, it can be set to expire at a specific time or after a certain interval using the timerfd_settime system call. The timerfd_gettime system call can be used to retrieve the current expiration time and interval.

To wait for timer expirations, a process can use standard I/O multiplexing functions like poll, select, or epoll on the timerfd file descriptor. When the timer expires, the file descriptor becomes readable, and a read operation on it will return the number of expirations that have occurred since the last read. This allows for efficient and event-driven handling of time-based events without requiring the use of signals or busy-waiting loops.