PTHREAD_GETCPUCLOCKID

Section: Linux Programmer's Manual (3)
Updated: 2020-11-01
Page Index

NAME

pthread_getcpuclockid - retrieve ID of a thread's CPU time clock

SYNOPSIS

#include <pthread.h>
#include <time.h>

int pthread_getcpuclockid(pthread_t thread, clockid_t *clockid);

Compile and link with -pthread.

DESCRIPTION

The pthread_getcpuclockid() function obtains the ID of the CPU-time clock of the thread whose ID is given in thread, and returns it in the location pointed to by clockid.

RETURN VALUE

On success, this function returns 0; on error, it returns a nonzero error number.

ERRORS

ENOENT: Per-thread CPU time clocks are not supported by the system.
ESRCH: No thread with the ID thread could be found.

VERSIONS

This 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
pthread_getcpuclockid()	Thread safety	MT-Safe

CONFORMING TO

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

NOTES

When thread refers to the calling thread, this function returns an identifier that refers to the same clock manipulated by clock_gettime(2) and clock_settime(2) when given the clock ID CLOCK_THREAD_CPUTIME_ID.

EXAMPLES

The program below creates a thread and then uses 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:

$ ./a.out 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

Program source

/* Link with "-lrt" */

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

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

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

static void * thread_start(void *arg) {
    printf("Subthread starting infinite loop\n");
    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\n", (intmax_t) ts.tv_sec, ts.tv_nsec / 1000000); }

int main(int argc, char *argv[]) {
    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\n");
sleep(1);

    printf("Main thread consuming some CPU time...\n");
    for (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 */ }

COLOPHON

This page is part of release 5.10 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/.