CLOCK_GETCPUCLOCKID(3)                                                  Linux Programmer's Manual                                                 CLOCK_GETCPUCLOCKID(3)

NAME
       clock_getcpuclockid - obtain ID of a process CPU-time clock

SYNOPSIS
       #include <time.h>

       int clock_getcpuclockid(pid_t pid, clockid_t *clockid);

       Link with -lrt (only for glibc versions before 2.17).

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

       clock_getcpuclockid():
           _POSIX_C_SOURCE >= 200112L

DESCRIPTION
       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.

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

ERRORS
       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 un‐
              less the kernel does not support obtaining the per-process CPU-time clock of another process.)

       ESRCH  There is no process with the ID pid.

VERSIONS
       The clock_getcpuclockid() 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   │
       ├──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │clock_getcpuclockid()                                                                                                                 │ Thread safety │ MT-Safe │
       └──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

CONFORMING TO
       POSIX.1-2001, POSIX.1-2008.

NOTES
       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.

EXAMPLES
       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

   Program source

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

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

Linux                                                                          2021-03-22                                                         CLOCK_GETCPUCLOCKID(3)