clock_getcpuclockid - obtain ID of a process CPU-time clock

       For an explanation of the terms used in this section, see attributes(7).
       ┌─────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                                                                   │ Attribute     │ Value   │
       ├─────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │ clock_getcpuclockid()                                                       │ Thread safety │ MT-Safe │
       └─────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

       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 clockid.  If pid is zero, then the clock ID of the CPU-time
       clock of the calling process is returned.

ENOSYS The  kernel  does not support obtaining the per-process CPU-time clock of another process, and pid
              does not specify the calling process.

       EPERM  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.)

       ESRCH  There is no process with the ID pid.

       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.out1                 # Show CPU clock of init process
           CPU-time clock for PID 1 is 2.213466748 seconds

   Programsource

       #define _XOPEN_SOURCE 600
       #include <stdint.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <time.h>
       #include <unistd.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 %jd.%09ld seconds\n",
                  argv[1], (intmax_t) ts.tv_sec, ts.tv_nsec);
           exit(EXIT_SUCCESS);
       }

       glibc 2.2.  POSIX.1-2001.

       Standard C library (libc, -lc), since glibc 2.17

       Before glibc 2.17, Real-time library (librt, -lrt)

       clock_getcpuclockid - obtain ID of a process CPU-time clock

       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.

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

clock_getres(2), timer_create(2), pthread_getcpuclockid(3), time(7)

Linux man-pages 6.9.1                              2024-06-15                             clock_getcpuclockid(3)

       POSIX.1-2008.

#include<time.h>intclock_getcpuclockid(pid_tpid,clockid_t*clockid);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       clock_getcpuclockid():
           _POSIX_C_SOURCE >= 200112L