man3/get_nprocs_conf.3

   1 .\" Copyright (c) 2012, Petr Benas
   2 .\" and Copyright (c) 2012, Michael Kerrisk <mtk.man-pages@gmail.com>
   3 .\"
   4 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   5 .\"
   6 .TH GET_NPROCS 3   2021-03-22 "GNU" "Linux Programmer's Manual"
   7 .SH NAME
   8 get_nprocs, get_nprocs_conf \- get number of processors
   9 .SH LIBRARY
  10 Standard C library
  11 .RI ( libc ", " \-lc )
  12 .SH SYNOPSIS
  13 .nf
  14 .B #include <sys/sysinfo.h>
  15 .PP
  16 .B int get_nprocs(void);
  17 .B int get_nprocs_conf(void);
  18 .fi
  19 .SH DESCRIPTION
  20 The function
  21 .BR get_nprocs_conf ()
  22 returns the number of processors configured by the operating system.
  23 .PP
  24 The function
  25 .BR get_nprocs ()
  26 returns the number of processors currently available in the system.
  27 This may be less than the number returned by
  28 .BR get_nprocs_conf ()
  29 because processors may be offline (e.g., on hotpluggable systems).
  30 .SH RETURN VALUE
  31 As given in DESCRIPTION.
  32 .SH ATTRIBUTES
  33 For an explanation of the terms used in this section, see
  34 .BR attributes (7).
  35 .ad l
  36 .nh
  37 .TS
  38 allbox;
  39 lbx lb lb
  40 l l l.
  41 Interface       Attribute       Value
  42 T{
  43 .BR get_nprocs (),
  44 .BR get_nprocs_conf ()
  45 T}      Thread safety   MT-Safe
  46 .TE
  47 .hy
  48 .ad
  49 .sp 1
  50 .SH CONFORMING TO
  51 These functions are GNU extensions.
  52 .SH NOTES
  53 The current
  54 .\" glibc 2.15
  55 implementation of these functions is rather expensive,
  56 since they open and parse files in the
  57 .I /sys
  58 filesystem each time they are called.
  59 .PP
  60 The following
  61 .BR sysconf (3)
  62 calls make use of the functions documented on this page
  63 to return the same information.
  64 .PP
  65 .in +4n
  66 .EX
  67 np = sysconf(_SC_NPROCESSORS_CONF);     /* processors configured */
  68 np = sysconf(_SC_NPROCESSORS_ONLN);     /* processors available */
  69 .EE
  70 .in
  71 .SH EXAMPLES
  72 The following example shows how
  73 .BR get_nprocs ()
  74 and
  75 .BR get_nprocs_conf ()
  76 can be used.
  77 .PP
  78 .EX
  79 #include <stdlib.h>
  80 #include <stdio.h>
  81 #include <sys/sysinfo.h>
  82
  83 int
  84 main(int argc, char *argv[])
  85 {
  86     printf("This system has %d processors configured and "
  87             "%d processors available.\en",
  88             get_nprocs_conf(), get_nprocs());
  89     exit(EXIT_SUCCESS);
  90 }
  91 .EE
  92 .SH SEE ALSO
  93 .BR nproc (1)