_syscall.2, clock_getres.2, clone.2, copy_file_range.2, create_module.2, delete_modul...

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

.\" Copyright 2008 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
.\"
.TH RANDOM_R 3  2017-03-13 "GNU" "Linux Programmer's Manual"
.SH NAME
random_r, srandom_r, initstate_r, setstate_r \- reentrant
random number generator
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.PP
.BI "int random_r(struct random_data *" buf ", int32_t *" result );
.PP
.BI "int srandom_r(unsigned int " seed ", struct random_data *" buf );
.PP
.BI "int initstate_r(unsigned int " seed ", char *" statebuf ,
.BI "                size_t " statelen ", struct random_data *" buf );
.PP
.BI "int setstate_r(char *" statebuf ", struct random_data *" buf );
.fi
.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.PP
.ad l
.BR random_r (),
.BR srandom_r (),
.BR initstate_r (),
.BR setstate_r ():
.RS 4
/* Glibc since 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
.RE
.ad b
.SH DESCRIPTION
These functions are the reentrant equivalents
of the functions described in
.BR random (3).
They are suitable for use in multithreaded programs where each thread
needs to obtain an independent, reproducible sequence of random numbers.

The
.BR random_r ()
function is like
.BR random (3),
except that instead of using state information maintained
in a global variable,
it uses the state information in the argument pointed to by
.IR buf ,
which must have been previously initialized by
.BR initstate_r ().
The generated random number is returned in the argument
.IR result .

The
.BR srandom_r ()
function is like
.BR srandom (3),
except that it initializes the seed for the random number generator
whose state is maintained in the object pointed to by
.IR buf ,
which must have been previously initialized by
.BR initstate_r (),
instead of the seed associated with the global state variable.

The
.BR initstate_r ()
function is like
.BR initstate (3)
except that it initializes the state in the object pointed to by
.IR buf ,
rather than initializing the global state variable.
Before calling this function, the
.IR buf.state
field must be initialized to NULL.
The
.BR initstate_r ()
function records a pointer to the
.I statebuf
argument inside the structure pointed to by
.IR buf .
Thus,
.IR statebuf
should not be deallocated so long as
.IR buf
is still in use.
(So,
.I statebuf
should typically be allocated as a static variable,
or allocated on the heap using
.BR malloc (3)
or similar.)

The
.BR setstate_r ()
function is like
.BR setstate (3)
except that it modifies the state in the object pointed to by
.IR buf ,
rather than modifying the global state variable.
\fIstate\fP must first have been initialized
using
.BR initstate_r ()
or be the result of a previous call of
.BR setstate_r ().
.SH RETURN VALUE
All of these functions return 0 on success.
On error, \-1 is returned, with
.I errno
set to indicate the cause of the error.
.SH ERRORS
.TP
.B EINVAL
A state array of less than 8 bytes was specified to
.BR initstate_r ().
.TP
.B EINVAL
The
.I statebuf
or
.I buf
argument to
.BR setstate_r ()
was NULL.
.TP
.B EINVAL
The
.I buf
or
.I result
argument to
.BR random_r ()
was NULL.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbw27 lb lb
l l l.
Interface	Attribute	Value
T{
.BR random_r (),
.BR srandom_r (),
.br
.BR initstate_r (),
.BR setstate_r ()
T}	Thread safety	MT-Safe race:buf
.TE
.SH CONFORMING TO
These functions are nonstandard glibc extensions.
.\" These functions appear to be on Tru64, but don't seem to be on
.\" Solaris, HP-UX, or FreeBSD.
.SH BUGS
The
.BR initstate_r ()
interface is confusing.
.\" FIXME . https://sourceware.org/bugzilla/show_bug.cgi?id=3662
It appears that the
.IR random_data
type is intended to be opaque,
but the implementation requires the user to either initialize the
.I buf.state
file to NULL or zero out the entire structure before the call.
.SH SEE ALSO
.BR drand48 (3),
.BR rand (3),
.BR random (3)