'\" t
.\" Copyright (c) 2009 Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH pthread_getcpuclockid 3 2023-03-30 "Linux man-pages 6.04"
.SH NAME
pthread_getcpuclockid \- retrieve ID of a thread's CPU time clock
.SH LIBRARY
POSIX threads library
.RI ( libpthread ", " \-lpthread )
.SH SYNOPSIS
.nf
.B #include <pthread.h>
.B #include <time.h>
.PP
.BI "int pthread_getcpuclockid(pthread_t " thread ", clockid_t *" clockid );
.fi
.SH DESCRIPTION
The
.BR pthread_getcpuclockid ()
function obtains the ID of the CPU-time clock of the thread whose ID is
given in
.IR thread ,
and returns it in the location pointed to by
.IR clockid .
.\" The clockid is constructed as follows:
.\" *clockid = CLOCK_THREAD_CPUTIME_ID | (pd->tid << CLOCK_IDFIELD_SIZE)
.\" where CLOCK_IDFIELD_SIZE is 3.
.SH RETURN VALUE
On success, this function returns 0;
on error, it returns a nonzero error number.
.SH ERRORS
.TP
.B ENOENT
.\" CLOCK_THREAD_CPUTIME_ID not defined
Per-thread CPU time clocks are not supported by the system.
.\"
.\" Looking at nptl/pthread_getcpuclockid.c an ERANGE error would
.\" be possible if kernel thread IDs took more than 29 bits (which
.\" they currently cannot).
.TP
.B ESRCH
No thread with the ID
.I thread
could be found.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR pthread_getcpuclockid ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH STANDARDS
POSIX.1-2008.
.SH HISTORY
glibc 2.2.
POSIX.1-2001.
.SH NOTES
When
.I thread
refers to the calling thread,
this function returns an identifier that refers to the same clock
manipulated by
.BR clock_gettime (2)
and
.BR clock_settime (2)
when given the clock ID
.BR CLOCK_THREAD_CPUTIME_ID .
.SH EXAMPLES
The program below creates a thread and then uses
.BR clock_gettime (2)
to retrieve the total process CPU time,
and the per-thread CPU time consumed by the two threads.
The following shell session shows an example run:
.PP
.in +4n
.EX
$ \fB./a.out\fP
Main thread sleeping
Subthread starting infinite loop
Main thread consuming some CPU time...
Process total CPU time:    1.368
Main thread CPU time:      0.376
Subthread CPU time:        0.992
.EE
.in
.SS Program source
\&
.\" SRC BEGIN (pthread_getcpuclockid.c)
.EX
/* Link with "\-lrt" */

#include <errno.h>
#include <pthread.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#define handle_error(msg) \e
        do { perror(msg); exit(EXIT_FAILURE); } while (0)

#define handle_error_en(en, msg) \e
        do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)

static void *
thread_start(void *arg)
{
    printf("Subthread starting infinite loop\en");
    for (;;)
        continue;
}

static void
pclock(char *msg, clockid_t cid)
{
    struct timespec ts;

    printf("%s", msg);
    if (clock_gettime(cid, &ts) == \-1)
        handle_error("clock_gettime");
    printf("%4jd.%03ld\en", (intmax_t) ts.tv_sec, ts.tv_nsec / 1000000);
}

int
main(void)
{
    pthread_t thread;
    clockid_t cid;
    int s;

    s = pthread_create(&thread, NULL, thread_start, NULL);
    if (s != 0)
        handle_error_en(s, "pthread_create");

    printf("Main thread sleeping\en");
    sleep(1);

    printf("Main thread consuming some CPU time...\en");
    for (unsigned int j = 0; j < 2000000; j++)
        getppid();

    pclock("Process total CPU time: ", CLOCK_PROCESS_CPUTIME_ID);

    s = pthread_getcpuclockid(pthread_self(), &cid);
    if (s != 0)
        handle_error_en(s, "pthread_getcpuclockid");
    pclock("Main thread CPU time:   ", cid);

    /* The preceding 4 lines of code could have been replaced by:
       pclock("Main thread CPU time:   ", CLOCK_THREAD_CPUTIME_ID); */

    s = pthread_getcpuclockid(thread, &cid);
    if (s != 0)
        handle_error_en(s, "pthread_getcpuclockid");
    pclock("Subthread CPU time: 1    ", cid);

    exit(EXIT_SUCCESS);         /* Terminates both threads */
}
.EE
.\" SRC END
.SH SEE ALSO
.BR clock_gettime (2),
.BR clock_settime (2),
.BR timer_create (2),
.BR clock_getcpuclockid (3),
.BR pthread_self (3),
.BR pthreads (7),
.BR time (7)