| .\" 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| .\" manual page may be incorrect or out-of-date.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 2017-09-15 "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. |
| .PP |
| 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 . |
| .PP |
| 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. |
| .PP |
| 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.) |
| .PP |
| 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 |
| field to NULL or zero out the entire structure before the call. |
| .SH SEE ALSO |
| .BR drand48 (3), |
| .BR rand (3), |
| .BR random (3) |