Name

clock_getcpuclockid — obtain ID of a process CPU-time clock

Synopsis

#include <time.h>
int clock_getcpuclockid( pid_t pid,
  clockid_t *clock_id);
 
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
clock_getcpuclockid():
_POSIX_C_SOURCE >= 200112L
[Note] Note

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

DESCRIPTION

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.

RETURN VALUE

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

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 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.

VERSIONS

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

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
clock_getcpuclockid() Thread safety MT-Safe

CONFORMING TO

POSIX.1-2001, POSIX.1-2008.

NOTES

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.

EXAMPLE

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);
}

SEE ALSO

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

COLOPHON

This page is part of release 4.16 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man−pages/.


  Copyright (c) 2008, Linux Foundation, written by Michael Kerrisk
<mtk.manpagesgmail.com>

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