pthread_getcpuclockid(3)

💖 pthread_getcpuclockid(3) 💖

okay bestie, so this one lives in the Library Functions Manual, and it's part of the POSIX threads library (libpthread, -lpthread) 🧵✨ — yes THAT library, the one you link with -lpthread. Come sit, we're gonna learn about clocks for threads. 🕰️

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🌸 NAME 🌸

pthread_getcpuclockid — grab the ID of a thread's CPU time clock 🎀

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📚 LIBRARY 📚

POSIX threads library (libpthread, -lpthread) 🫶

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✨ SYNOPSIS ✨

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

int pthread_getcpuclockid(pthread_t thread, clockid_t *clockid);

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🦋 DESCRIPTION 🦋

So pthread_getcpuclockid() literally goes and obtains the ID of the CPU-time clock of the thread whose ID you handed it in thread 💅 and then it returns that ID in the location pointed to by clockid. That's it. That's the whole thing. Iconic, honestly. 👑

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⭐ RETURN VALUE ⭐

• On success, this function returns 0 — slay. 🎉
• On error, it returns a nonzero error number. 💀 (not an errno situation, bestie, it hands you the error number directly, no cap.)

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💀 ERRORS 💀

• ENOENT — Per-thread CPU time clocks aren't supported by the system. 😭 The system said "we don't do that here."
• ESRCH — No thread with the ID thread could be found. 🙈 Like, who?? Nobody, apparently.

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🧚 ATTRIBUTES 🧚

For an explanation of the terms used in this section, go peek at attributes(7) 📖

• Interface: pthread_getcpuclockid()
• Attribute: Thread safety
• Value: MT-Safe 🔥 (yes, it's safe to call from multiple threads, you're welcome)

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👑 STANDARDS 👑

POSIX.1-2008. 💜

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🌈 HISTORY 🌈

• glibc 2.2. ⭐
• POSIX.1-2001. 🕰️

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🍓 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. 🎀 So like… same clock, different name tag. iykyk. 💅

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🔥 EXAMPLES 🔥

The program below creates a thread and then uses clock_gettime(2) to retrieve the total process CPU time, plus 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 <err.h>
#include <errno.h>
#include <pthread.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/time.h>
#include <time.h>
#include <unistd.h>

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)
        err(EXIT_FAILURE, "clock_gettime");
    printf("%4jd.%03ld\n", (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)
        errc(EXIT_FAILURE, s, "pthread_create");

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

    printf("Main thread consuming some CPU time...\n");
    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)
        errc(EXIT_FAILURE, 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)
        errc(EXIT_FAILURE, s, "pthread_getcpuclockid");
    pclock("Subthread CPU time: 1    ", cid);

    exit(EXIT_SUCCESS);         /* Terminates both threads */
}

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🫶 SEE ALSO 🫶

clock_gettime(2), clock_settime(2), timer_create(2), clock_getcpuclockid(3), pthread_self(3), pthreads(7), time(7)

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and that's the whole page, bestie 💖 this came from Linux man-pages 6.20, dated 2025-08-20 — go forth and clock those threads, main character 🕰️👑✨