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)