man3/clock_getcpuclockid.3

   1 '\" t
   2 .\" Copyright (c) 2008, Linux Foundation, written by Michael Kerrisk
   3 .\" <mtk.manpages@gmail.com>
   4 .\"
   5 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   6 .\"
   7 .TH clock_getcpuclockid 3 (date) "Linux man-pages (unreleased)"
   8 .SH NAME
   9 clock_getcpuclockid \- obtain ID of a process CPU-time clock
  10 .SH LIBRARY
  11 Standard C library
  12 .RI ( libc ", " \-lc ),
  13 since glibc 2.17
  14 .PP
  15 Before glibc 2.17,
  16 Real-time library
  17 .RI ( librt ", " \-lrt )
  18 .SH SYNOPSIS
  19 .B #include <time.h>
  20 .nf
  21 .PP
  22 .BI "int clock_getcpuclockid(pid_t " pid ", clockid_t *" clockid );
  23 .fi
  24 .PP
  25 .ad l
  26 .RS -4
  27 Feature Test Macro Requirements for glibc (see
  28 .BR feature_test_macros (7)):
  29 .RE
  30 .PP
  31 .BR clock_getcpuclockid ():
  32 .nf
  33     _POSIX_C_SOURCE >= 200112L
  34 .fi
  35 .SH DESCRIPTION
  36 The
  37 .BR clock_getcpuclockid ()
  38 function obtains the ID of the CPU-time clock of the process whose ID is
  39 .IR pid ,
  40 and returns it in the location pointed to by
  41 .IR clockid .
  42 If
  43 .I pid
  44 is zero, then the clock ID of the CPU-time clock
  45 of the calling process is returned.
  46 .SH RETURN VALUE
  47 On success,
  48 .BR clock_getcpuclockid ()
  49 returns 0;
  50 on error, it returns one of the positive error numbers listed in ERRORS.
  51 .SH ERRORS
  52 .TP
  53 .B ENOSYS
  54 The kernel does not support obtaining the per-process
  55 CPU-time clock of another process, and
  56 .I pid
  57 does not specify the calling process.
  58 .TP
  59 .B EPERM
  60 The caller does not have permission to access
  61 the CPU-time clock of the process specified by
  62 .IR pid .
  63 (Specified in POSIX.1-2001;
  64 does not occur on Linux unless the kernel does not support
  65 obtaining the per-process CPU-time clock of another process.)
  66 .TP
  67 .B ESRCH
  68 There is no process with the ID
  69 .IR pid .
  70 .SH ATTRIBUTES
  71 For an explanation of the terms used in this section, see
  72 .BR attributes (7).
  73 .TS
  74 allbox;
  75 lbx lb lb
  76 l l l.
  77 Interface       Attribute       Value
  78 T{
  79 .na
  80 .nh
  81 .BR clock_getcpuclockid ()
  82 T}      Thread safety   MT-Safe
  83 .TE
  84 .sp 1
  85 .SH STANDARDS
  86 POSIX.1-2008.
  87 .SH HISTORY
  88 glibc 2.2.
  89 POSIX.1-2001.
  90 .SH NOTES
  91 Calling
  92 .BR clock_gettime (2)
  93 with the clock ID obtained by a call to
  94 .BR clock_getcpuclockid ()
  95 with a
  96 .I pid
  97 of 0,
  98 is the same as using the clock ID
  99 .BR CLOCK_PROCESS_CPUTIME_ID .
 100 .SH EXAMPLES
 101 The example program below obtains the
 102 CPU-time clock ID of the process whose ID is given on the command line,
 103 and then uses
 104 .BR clock_gettime (2)
 105 to obtain the time on that clock.
 106 An example run is the following:
 107 .PP
 108 .in +4n
 109 .EX
 110 .RB "$" " ./a.out 1" "                 # Show CPU clock of init process"
 111 CPU\-time clock for PID 1 is 2.213466748 seconds
 112 .EE
 113 .in
 114 .SS Program source
 115 \&
 116 .\" SRC BEGIN (clock_getcpuclockid.c)
 117 .EX
 118 #define _XOPEN_SOURCE 600
 119 #include <stdint.h>
 120 #include <stdio.h>
 121 #include <stdlib.h>
 122 #include <time.h>
 123 #include <unistd.h>
 124 \&
 125 int
 126 main(int argc, char *argv[])
 127 {
 128     clockid_t clockid;
 129     struct timespec ts;
 130 \&
 131     if (argc != 2) {
 132         fprintf(stderr, "%s <process\-ID>\en", argv[0]);
 133         exit(EXIT_FAILURE);
 134     }
 135 \&
 136     if (clock_getcpuclockid(atoi(argv[1]), &clockid) != 0) {
 137         perror("clock_getcpuclockid");
 138         exit(EXIT_FAILURE);
 139     }
 140 \&
 141     if (clock_gettime(clockid, &ts) == \-1) {
 142         perror("clock_gettime");
 143         exit(EXIT_FAILURE);
 144     }
 145 \&
 146     printf("CPU\-time clock for PID %s is %jd.%09ld seconds\en",
 147            argv[1], (intmax_t) ts.tv_sec, ts.tv_nsec);
 148     exit(EXIT_SUCCESS);
 149 }
 150 .EE
 151 .\" SRC END
 152 .SH SEE ALSO
 153 .BR clock_getres (2),
 154 .BR timer_create (2),
 155 .BR pthread_getcpuclockid (3),
 156 .BR time (7)