clock_getcpuclockid (3)

#include <time.h>

int clock_getcpuclockid(pid_t pid, clockid_t *clock_id);

Link with -lrt (only for glibc versions before 2.17).

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

clock_getcpuclockid():

_XOPEN_SOURCE >= 600 || _POSIX_C_SOURCE >= 200112L

The clock_getcpuclockid() function obtains the ID of the CPU-time clock of the process whose ID is pid, and returns it in the location pointed to by clock_id. If pid is zero, then the clock ID of the CPU-time clock of the calling process is returned.

On success, clock_getcpuclockid() returns 0; on error, it returns one of the positive error numbers listed in ERRORS.

ENOSYS

The kernel does not support obtaining the per-process CPU-time clock of another process, and pid does not specify the calling process.

EPERM

The caller does not have permission to access the CPU-time clock of the process specified by pid. (Specified as an optional error in POSIX.1-2001; does not occur on Linux unless the kernel does not support obtaining the per-process CPU-time clock of another process.)

ESRCH

There is no process with the ID pid.

The clock_getcpuclockid() function is available in glibc since version 2.2.

Multithreading (see pthreads(7))

The clock_getcpuclockid() function is thread-safe.

POSIX.1-2001.

Calling clock_gettime(2) with the clock ID obtained by a call to clock_getcpuclockid() with a pid of 0, is the same as using the clock ID CLOCK_PROCESS_CPUTIME_ID.

The example program below obtains the CPU-time clock ID of the process whose ID is given on the command line, and then uses clock_gettime(2) to obtain the time on that clock. An example run is the following:

$ ./a.out 1                 # Show CPU clock of init process
CPU-time clock for PID 1 is 2.213466748 seconds

Program source

#define _XOPEN_SOURCE 600
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <time.h>

int
main(int argc, char *argv[])
{
    clockid_t clockid;
    struct timespec ts;

    if (argc != 2) {
        fprintf(stderr, "%s <process-ID>\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    if (clock_getcpuclockid(atoi(argv[1]), &clockid) != 0) {
        perror("clock_getcpuclockid");
        exit(EXIT_FAILURE);
    }

    if (clock_gettime(clockid, &ts) == -1) {
        perror("clock_gettime");
        exit(EXIT_FAILURE);
    }

    printf("CPU-time clock for PID %s is %ld.%09ld seconds\n",
            argv[1], (long) ts.tv_sec, (long) ts.tv_nsec);
    exit(EXIT_SUCCESS);
}

clock_getres(2), timer_create(2), pthread_getcpuclockid(3), time(7)

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