Why are both tv_sec and tv_usec significant in determining the duration of a timer?

Question

The manual page getitimer(2) claims that

both tv_sec and tv_usec significant in determining the duration of a timer

It doesn't go on to say why that is. In many examples that I have come across tv_sec is simply set to 0, while tv_usec is given some reasonable value, or vis versa. Are these timers counting down simultaneously, or is the total countdown time tv_sec + tv_usec? Should I use both? Neither?

Answer 1

The man page documents the timeval structure:

struct timeval {
    long tv_sec;                /* seconds */
    long tv_usec;               /* microseconds */
};

If you want to wait a whole number of seconds, you'd just set tv_sec. If you want to wait a portion of a second, you'd set tv_usec. If you want to wait 4.5 seconds, you'd set both of them to appropriate values (4 and 500000, respectively)

Answer 2

Yes, the total time is the sum of both. tv_sec is the seconds. And tv_usec is microseconds beyond that.