man3/random_r.3

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  26 .TH RANDOM_R 3  2017-09-15 "GNU" "Linux Programmer's Manual"
  27 .SH NAME
  28 random_r, srandom_r, initstate_r, setstate_r \- reentrant
  29 random number generator
  30 .SH SYNOPSIS
  31 .nf
  32 .B #include <stdlib.h>
  33 .PP
  34 .BI "int random_r(struct random_data *" buf ", int32_t *" result );
  35 .PP
  36 .BI "int srandom_r(unsigned int " seed ", struct random_data *" buf );
  37 .PP
  38 .BI "int initstate_r(unsigned int " seed ", char *" statebuf ,
  39 .BI "                size_t " statelen ", struct random_data *" buf );
  40 .PP
  41 .BI "int setstate_r(char *" statebuf ", struct random_data *" buf );
  42 .fi
  43 .PP
  44 .in -4n
  45 Feature Test Macro Requirements for glibc (see
  46 .BR feature_test_macros (7)):
  47 .in
  48 .PP
  49 .ad l
  50 .BR random_r (),
  51 .BR srandom_r (),
  52 .BR initstate_r (),
  53 .BR setstate_r ():
  54 .RS 4
  55 /* Glibc since 2.19: */ _DEFAULT_SOURCE
  56     || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
  57 .RE
  58 .ad b
  59 .SH DESCRIPTION
  60 These functions are the reentrant equivalents
  61 of the functions described in
  62 .BR random (3).
  63 They are suitable for use in multithreaded programs where each thread
  64 needs to obtain an independent, reproducible sequence of random numbers.
  65 .PP
  66 The
  67 .BR random_r ()
  68 function is like
  69 .BR random (3),
  70 except that instead of using state information maintained
  71 in a global variable,
  72 it uses the state information in the argument pointed to by
  73 .IR buf ,
  74 which must have been previously initialized by
  75 .BR initstate_r ().
  76 The generated random number is returned in the argument
  77 .IR result .
  78 .PP
  79 The
  80 .BR srandom_r ()
  81 function is like
  82 .BR srandom (3),
  83 except that it initializes the seed for the random number generator
  84 whose state is maintained in the object pointed to by
  85 .IR buf ,
  86 which must have been previously initialized by
  87 .BR initstate_r (),
  88 instead of the seed associated with the global state variable.
  89 .PP
  90 The
  91 .BR initstate_r ()
  92 function is like
  93 .BR initstate (3)
  94 except that it initializes the state in the object pointed to by
  95 .IR buf ,
  96 rather than initializing the global state variable.
  97 Before calling this function, the
  98 .IR buf.state
  99 field must be initialized to NULL.
 100 The
 101 .BR initstate_r ()
 102 function records a pointer to the
 103 .I statebuf
 104 argument inside the structure pointed to by
 105 .IR buf .
 106 Thus,
 107 .IR statebuf
 108 should not be deallocated so long as
 109 .IR buf
 110 is still in use.
 111 (So,
 112 .I statebuf
 113 should typically be allocated as a static variable,
 114 or allocated on the heap using
 115 .BR malloc (3)
 116 or similar.)
 117 .PP
 118 The
 119 .BR setstate_r ()
 120 function is like
 121 .BR setstate (3)
 122 except that it modifies the state in the object pointed to by
 123 .IR buf ,
 124 rather than modifying the global state variable.
 125 \fIstate\fP must first have been initialized
 126 using
 127 .BR initstate_r ()
 128 or be the result of a previous call of
 129 .BR setstate_r ().
 130 .SH RETURN VALUE
 131 All of these functions return 0 on success.
 132 On error, \-1 is returned, with
 133 .I errno
 134 set to indicate the cause of the error.
 135 .SH ERRORS
 136 .TP
 137 .B EINVAL
 138 A state array of less than 8 bytes was specified to
 139 .BR initstate_r ().
 140 .TP
 141 .B EINVAL
 142 The
 143 .I statebuf
 144 or
 145 .I buf
 146 argument to
 147 .BR setstate_r ()
 148 was NULL.
 149 .TP
 150 .B EINVAL
 151 The
 152 .I buf
 153 or
 154 .I result
 155 argument to
 156 .BR random_r ()
 157 was NULL.
 158 .SH ATTRIBUTES
 159 For an explanation of the terms used in this section, see
 160 .BR attributes (7).
 161 .TS
 162 allbox;
 163 lbw27 lb lb
 164 l l l.
 165 Interface       Attribute       Value
 166 T{
 167 .BR random_r (),
 168 .BR srandom_r (),
 169 .br
 170 .BR initstate_r (),
 171 .BR setstate_r ()
 172 T}      Thread safety   MT-Safe race:buf
 173 .TE
 174 .SH CONFORMING TO
 175 These functions are nonstandard glibc extensions.
 176 .\" These functions appear to be on Tru64, but don't seem to be on
 177 .\" Solaris, HP-UX, or FreeBSD.
 178 .SH BUGS
 179 The
 180 .BR initstate_r ()
 181 interface is confusing.
 182 .\" FIXME . https://sourceware.org/bugzilla/show_bug.cgi?id=3662
 183 It appears that the
 184 .IR random_data
 185 type is intended to be opaque,
 186 but the implementation requires the user to either initialize the
 187 .I buf.state
 188 field to NULL or zero out the entire structure before the call.
 189 .SH SEE ALSO
 190 .BR drand48 (3),
 191 .BR rand (3),
 192 .BR random (3)