[thirdparty/man-pages.git] / man3 / get_nprocs_conf.3

.\" Copyright (c) 2012, Petr Benas
.\" and Copyright (c) 2012, Michael Kerrisk <mtk.man-pages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH GET_NPROCS 3 (date) "Linux man-pages (unreleased)"
.SH NAME
get_nprocs, get_nprocs_conf \- get number of processors
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <sys/sysinfo.h>
.PP
.B int get_nprocs(void);
.B int get_nprocs_conf(void);
.fi
.SH DESCRIPTION
The function
.BR get_nprocs_conf ()
returns the number of processors configured by the operating system.
.PP
The function
.BR get_nprocs ()
returns the number of processors currently available in the system.
This may be less than the number returned by
.BR get_nprocs_conf ()
because processors may be offline (e.g., on hotpluggable systems).
.SH RETURN VALUE
As given in DESCRIPTION.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR get_nprocs (),
.BR get_nprocs_conf ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH STANDARDS
These functions are GNU extensions.
.SH NOTES
The current
.\" glibc 2.15
implementation of these functions is rather expensive,
since they open and parse files in the
.I /sys
filesystem each time they are called.
.PP
The following
.BR sysconf (3)
calls make use of the functions documented on this page
to return the same information.
.PP
.in +4n
.EX
np = sysconf(_SC_NPROCESSORS_CONF);     /* processors configured */
np = sysconf(_SC_NPROCESSORS_ONLN);     /* processors available */
.EE
.in
.SH EXAMPLES
The following example shows how
.BR get_nprocs ()
and
.BR get_nprocs_conf ()
can be used.
.PP
.\" SRC BEGIN (get_nprocs_conf.c)
.EX
#include <stdio.h>
#include <stdlib.h>
#include <sys/sysinfo.h>

int
main(void)
{
    printf("This system has %d processors configured and "
            "%d processors available.\en",
            get_nprocs_conf(), get_nprocs());
    exit(EXIT_SUCCESS);
}
.EE
.\" SRC END
.SH SEE ALSO
.BR nproc (1)
Commit	Line	Data
	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 (date) "Linux man-pages (unreleased)"
	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 STANDARDS
	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	.\" SRC BEGIN (get_nprocs_conf.c)
	79	.EX
	80	#include <stdio.h>
	81	#include <stdlib.h>
	82	#include <sys/sysinfo.h>
	83
	84	int
	85	main(void)
	86	{
	87	printf("This system has %d processors configured and "
	88	"%d processors available.\en",
	89	get_nprocs_conf(), get_nprocs());
	90	exit(EXIT_SUCCESS);
	91	}
	92	.EE
	93	.\" SRC END
	94	.SH SEE ALSO
	95	.BR nproc (1)