clock_getcpuclockid - obtain ID of a process CPU-time clock

#include <time.h>
int clock_getcpuclockid(pid_t pid, clockid_t *clock_id);
Link with -lrt (only for glibc versions before 2.17).

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_POSIX_C_SOURCE >= 200112L

The clock_getcpuclockid() function obtains the ID of the CPU-time clock of the process whose ID is pid, and returns it in the location pointed to by clock_id. If pid is zero, then the clock ID of the CPU-time clock of the calling process is returned.

On success, clock_getcpuclockid() returns 0; on error, it returns one of the positive error numbers listed in ERRORS.

The kernel does not support obtaining the per-process CPU-time clock of another process, and pid does not specify the calling process.
The caller does not have permission to access the CPU-time clock of the process specified by pid. (Specified 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.)
There is no process with the ID pid.

The clock_getcpuclockid() 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
clock_getcpuclockid () Thread safety MT-Safe

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

Calling clock_gettime(2) with the clock ID obtained by a call to clock_getcpuclockid() with a pid of 0, is the same as using the clock ID CLOCK_PROCESS_CPUTIME_ID.

The example program below obtains the CPU-time clock ID of the process whose ID is given on the command line, and then uses clock_gettime(2) to obtain the time on that clock. An example run is the following:

$ ./a.out 1                 # Show CPU clock of init process
CPU-time clock for PID 1 is 2.213466748 seconds

#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); }

clock_getres(2), timer_create(2), pthread_getcpuclockid(3), time(7)
2019-03-06 Linux