diff options
Diffstat (limited to 'mysys/thr_mutex.c')
| -rw-r--r-- | mysys/thr_mutex.c | 27 |
1 files changed, 25 insertions, 2 deletions
diff --git a/mysys/thr_mutex.c b/mysys/thr_mutex.c index 49003553f0b..8f9928026ba 100644 --- a/mysys/thr_mutex.c +++ b/mysys/thr_mutex.c @@ -438,9 +438,33 @@ int my_pthread_fastmutex_init(my_pthread_fastmutex_t *mp, mp->spins= MY_PTHREAD_FASTMUTEX_SPINS; else mp->spins= 0; + mp->rng_state= 1; return pthread_mutex_init(&mp->mutex, attr); } +/** + Park-Miller random number generator. A simple linear congruential + generator that operates in multiplicative group of integers modulo n. + + x_{k+1} = (x_k g) mod n + + Popular pair of parameters: n = 2^32 − 5 = 4294967291 and g = 279470273. + The period of the generator is about 2^31. + Largest value that can be returned: 2147483646 (RAND_MAX) + + Reference: + + S. K. Park and K. W. Miller + "Random number generators: good ones are hard to find" + Commun. ACM, October 1988, Volume 31, No 10, pages 1192-1201. +*/ + +static double park_rng(my_pthread_fastmutex_t *mp) +{ + mp->rng_state= ((my_ulonglong)mp->rng_state * 279470273U) % 4294967291U; + return (mp->rng_state / 2147483647.0); +} + int my_pthread_fastmutex_lock(my_pthread_fastmutex_t *mp) { int res; @@ -458,8 +482,7 @@ int my_pthread_fastmutex_lock(my_pthread_fastmutex_t *mp) return res; mutex_delay(maxdelay); - maxdelay += ((double) random() / (double) RAND_MAX) * - MY_PTHREAD_FASTMUTEX_DELAY + 1; + maxdelay += park_rng(mp) * MY_PTHREAD_FASTMUTEX_DELAY + 1; } return pthread_mutex_lock(&mp->mutex); } |