NAME

       random_r, srandom_r, initstate_r, setstate_r - reentrant random number generator

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <stdlib.h>

       int random_r(struct random_data *restrict buf,
                    int32_t *restrict result);
       int srandom_r(unsigned int seed, struct random_data *buf);

       int initstate_r(unsigned int seed, char statebuf[restrict .statelen],
                    size_t statelen, struct random_data *restrict buf);
       int setstate_r(char *restrict statebuf,
                    struct random_data *restrict buf);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       random_r(), srandom_r(), initstate_r(), setstate_r():
           /* glibc >= 2.19: */ _DEFAULT_SOURCE
               || /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE

DESCRIPTION

       These functions are the reentrant equivalents of the functions described in random(3).  They are suitable
       for use in multithreaded programs where each thread needs to obtain an independent, reproducible sequence
       of random numbers.

       The random_r() function is like 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 buf, which  must  have  been
       previously initialized by initstate_r().  The generated random number is returned in the argument result.

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

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

       The setstate_r() function is like setstate(3) except that it modifies the state in the object pointed  to
       by  buf,  rather  than modifying the global state variable.  state must first have been initialized using
       initstate_r() or be the result of a previous call of setstate_r().

RETURN VALUE

       All of these functions return 0 on success.  On error, -1 is returned, with errno  set  to  indicate  the
       error.

ERRORS

       EINVAL A state array of less than 8 bytes was specified to initstate_r().

       EINVAL The statebuf or buf argument to setstate_r() was NULL.

       EINVAL The buf or result argument to random_r() was NULL.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌─────────────────────────────────────────────────────────────────────┬───────────────┬──────────────────┐
       │Interface                                                            │ Attribute     │ Value            │
       ├─────────────────────────────────────────────────────────────────────┼───────────────┼──────────────────┤
       │random_r(), srandom_r(), initstate_r(), setstate_r()                 │ Thread safety │ MT-Safe race:buf │
       └─────────────────────────────────────────────────────────────────────┴───────────────┴──────────────────┘

STANDARDS

       GNU.

BUGS

       The initstate_r() interface is confusing.  It appears that the random_data type is intended to be opaque,
       but the implementation requires the user to either initialize the buf.state field to NULL or zero out the
       entire structure before the call.

SEE ALSO

       drand48(3), rand(3), random(3)