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.\" Copyright (c) 2008, Linux Foundation, written by Michael Kerrisk
.\" <mtk.manpages@gmail.com>
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein. The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.TH CLOCK_GETCPUCLOCKID 3 2009-02-20 "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.
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR clock_getcpuclockid ():
_XOPEN_SOURCE\ >=\ 600
.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 a positive error number.
.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)
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