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.TH CLOCK_GETCPUCLOCKID 3 2012-10-29 "Linux" "Linux Programmer's Manual"
.SH NAME
clock_getcpuclockid \- obtain ID of a process CPU-time clock
.SH SYNOPSIS
.B #include <time.h>
.nf
.sp
.BI "int clock_getcpuclockid(pid_t " pid ", clockid_t *" clock_id );
.fi
.sp
Link with \fI\-lrt\fP (only for glibc versions before 2.17).
.sp
.ad l
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR clock_getcpuclockid ():
.RS 4
_XOPEN_SOURCE\ >=\ 600 || _POSIX_C_SOURCE\ >=\ 200112L
.RE
.ad
.SH DESCRIPTION
The
.BR clock_getcpuclockid ()
function obtains the ID of the CPU-time clock of the process whose ID is
.IR pid ,
and returns it in the location pointed to by
.IR clock_id .
If
.I pid
is zero, then the clock ID of the CPU-time clock
of the calling process is returned.
.SH RETURN VALUE
On success,
.BR clock_getcpuclockid ()
returns 0;
on error, it returns one of the positive error numbers listed in ERRORS.
.SH ERRORS
.TP
.B ENOSYS
The kernel does not support obtaining the per-process
CPU-time clock of another process, and
.I pid
does not specify the calling process.
.TP
.B EPERM
The caller does not have permission to access
the CPU-time clock of the process specified by
.IR 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.)
.TP
.B ESRCH
There is no process with the ID
.IR pid .
.SH VERSIONS
The
.BR clock_getcpuclockid ()
function is available in glibc since version 2.2.
.SH CONFORMING TO
POSIX.1-2001.
.SH NOTES
Calling
.BR clock_gettime (2)
with the clock ID obtained by a call to
.BR clock_getcpuclockid ()
with a
.I pid
of 0,
is the same as using the clock ID
.BR CLOCK_PROCESS_CPUTIME_ID .
.SH 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
.BR clock_gettime (2)
to obtain the time on that clock.
An example run is the following:
.in +4n
.nf

.RB "$" " ./a.out 1" "                 # Show CPU clock of init process"
CPU-time clock for PID 1 is 2.213466748 seconds
.fi
.in
.SS Program source
\&
.nf
#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);
}
.fi
.SH SEE ALSO
.BR clock_getres (2),
.BR timer_create (2),
.BR pthread_getcpuclockid (3),
.BR time (7)