nonexistent clocks

[Jan Stary]

Dear all,

the code below works for CLOCK_REALTIME and CLOCK_MONOTONIC,
but not for CLOCK_VIRTUAL or CLOCK_PROF. Why is that?

All of those are documented in clock_gettime(2) and
I don't see anything about some of them being special
or only available in some special contexts.

Running the code ends in

        clock: Invalid argument

which I suppose is the first EINVAL in ERRORS
(I am not _setting_ the clock):

        The clock_id argument does not specify a known clock.

Why are they "not known"?

Jan




#include <stdint.h>
#include <string.h>
#include <stdio.h>
#include <time.h>
#include <err.h>

void
show(clockid_t id, char* name)
{
        struct timespec ts;
        struct timespec cr;
        if (clock_gettime(id, &ts) == -1)
                err(1, NULL);
        if (clock_getres(id, &cr) == -1)
                err(1, NULL);
        printf("%s %10lld.%09ld s, res %5ld ns\n",
                name, ts.tv_sec, ts.tv_nsec, cr.tv_nsec);
}

int
main(void)
{
        show(CLOCK_REALTIME,  "real time");
        show(CLOCK_MONOTONIC, "monotonic");
        show(CLOCK_VIRTUAL,   "virtual  ");
        show(CLOCK_PROF,      "prof     ");
        return 0;
}