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

#include <pthread.h>
#include <time.h>
int pthread_getcpuclockid(pthread_t thread, clockid_t *clock_id);
Compile and link with  -pthread.

The pthread_getcpuclockid() function returns the clock ID for the CPU time clock of the thread thread.

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

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

This function is available in glibc since version 2.2.

For an explanation of the terms used in this section, see attributes(7).
Interface Attribute Value
pthread_getcpuclockid () Thread safety MT-Safe

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

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.

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

/* Link with "-lrt" */
#include <time.h> #include <stdio.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("%4ld.%03ld\n", ts.tv_sec, ts.tv_nsec / 1000000); }
int main(int argc, char *argv[]) { pthread_t thread; clockid_t cid; int j, 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 (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 */ }

clock_gettime(2), clock_settime(2), timer_create(2), clock_getcpuclockid(3), pthread_self(3), pthreads(7), time(7)
2019-03-06 Linux