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Ensure thread safe through use of spinlock; add further comments.

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This commit is contained in:
counterpoint
2015-08-28 09:12:41 +01:00
parent c01aa6952e
commit 0d62f52812
1 changed files with 34 additions and 14 deletions
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48
server/core/random_jkiss.c
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@ -18,6 +18,9 @@
/** /**
* @file random_jkiss.c - Random number generator for the MariaDB Corporation MaxScale * @file random_jkiss.c - Random number generator for the MariaDB Corporation MaxScale
*
* See http://www0.cs.ucl.ac.uk/staff/d.jones/GoodPracticeRNG.pdf for discussion of random
* number generators (RNGs).
* *
* @verbatim * @verbatim
* Revision History * Revision History
@ -35,15 +38,22 @@
#include <unistd.h> #include <unistd.h>
#include <random_jkiss.h> #include <random_jkiss.h>
/* Public domain code for JKISS RNG - Comments added */ /* Public domain code for JKISS RNG - Comment header added */
/* If possible, the seed variables will be set from /dev/urandom but
* should that fail, these arbitrary numbers will be used as a last resort.
*/
static unsigned int x = 123456789,y = 987654321,z = 43219876,c = 6543217; /* Seed variables */ static unsigned int x = 123456789,y = 987654321,z = 43219876,c = 6543217; /* Seed variables */
static bool init = false; static bool init = false;
static void random_init_jkiss(); static SPINLOCK random_jkiss_spinlock = SPINLOCK_INIT;
static unsigned int random_jkiss_devrand(void);
static void random_init_jkiss(void);
/*** /***
* *
* Return a random number * Return a pseudo-random number that satisfies major tests for random sequences
* *
* @return uint Random number * @return uint Random number
* *
@ -52,9 +62,13 @@ unsigned int
random_jkiss(void) random_jkiss(void)
{ {
unsigned long long t; unsigned long long t;
unsigned int result;
spinlock_acquire(&random_jkiss_spinlock);
if (!init) if (!init)
{ {
/* Must set init first because initialisation calls this function */
init = true; init = true;
spinlock_release(&random_jkiss_spinlock);
random_init_jkiss(); random_init_jkiss();
} }
x = 314527869 * x + 1234567; x = 314527869 * x + 1234567;
@ -64,7 +78,9 @@ random_jkiss(void)
t = 4294584393ULL * z + c; t = 4294584393ULL * z + c;
c = t >> 32; c = t >> 32;
z = t; z = t;
return x + y + z; result = x + y + z;
spinlock_release(&random_jkiss_spinlock);
return result;
} }
/* Own code adapted from http://www0.cs.ucl.ac.uk/staff/d.jones/GoodPracticeRNG.pdf */ /* Own code adapted from http://www0.cs.ucl.ac.uk/staff/d.jones/GoodPracticeRNG.pdf */
@ -72,19 +88,21 @@ random_jkiss(void)
/*** /***
* *
* Obtain a seed random number from /dev/urandom if available. * Obtain a seed random number from /dev/urandom if available.
* Otherwise use constant values
* *
* @return uint Random number * @return uint Random number
* *
*/ */
static unsigned int static unsigned int
random_devrand() random_jkiss_devrand(void)
{ {
int fn; int fn;
unsigned int r; unsigned int r;
fn = open("/dev/urandom", O_RDONLY); if ((fn = open("/dev/urandom", O_RDONLY)) == -1) return 0;
if (fn == -1) return 0; if (read(fn, &r, 4) != 4)
if (read(fn, &r, 4) != 4) return 0; {
close(fn);
return 0;
}
close(fn); close(fn);
return r; return r;
} }
@ -96,13 +114,15 @@ random_devrand()
* *
*/ */
static void static void
random_init_jkiss() random_init_jkiss(void)
{ {
int newrand, i; int newrand, i;
if ((newrand = random_devrand()) != 0) x = newrand; if ((newrand = random_jkiss_devrand()) != 0) x = newrand;
if ((newrand = random_devrand()) != 0) y = newrand; if ((newrand = random_jkiss_devrand()) != 0) y = newrand;
if ((newrand = random_devrand()) != 0) z = newrand; if ((newrand = random_jkiss_devrand()) != 0) z = newrand;
if ((newrand = random_devrand()) != 0) if ((newrand = random_jkiss_devrand()) != 0)
c = newrand % 698769068 + 1; /* Should be less than 698769069 */ c = newrand % 698769068 + 1; /* Should be less than 698769069 */
/* "Warm up" our random number generator */
for (i = 0; i < 100; i++) random_jkiss(); for (i = 0; i < 100; i++) random_jkiss();
} }