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Add a global counter in ddsrt_random_init fallback

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It currently uses process id and timestamp, but on a low-resolution
clock that might result in two subsequent initialisations in the same
process yielding the same seed, and that wasn't the intent.

Signed-off-by: Erik Boasson <eb@ilities.com>
This commit is contained in:
Erik Boasson 2019-08-24 17:57:25 +02:00 • committed by eboasson
parent 68b85d0a2d
commit a632f80000
1 changed files with 4 additions and 1 deletions
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5
src/ddsrt/src/random.c
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@ -61,6 +61,7 @@
#include "dds/ddsrt/sync.h" #include "dds/ddsrt/sync.h"
#include "dds/ddsrt/time.h" #include "dds/ddsrt/time.h"
#include "dds/ddsrt/process.h" #include "dds/ddsrt/process.h"
#include "dds/ddsrt/atomics.h"
#include "dds/ddsrt/static_assert.h" #include "dds/ddsrt/static_assert.h"
#define N DDSRT_MT19937_N #define N DDSRT_MT19937_N
@ -186,13 +187,15 @@ void ddsrt_random_init (void)
ddsrt_prng_seed_t seed; ddsrt_prng_seed_t seed;
if (!ddsrt_prng_makeseed (&seed)) if (!ddsrt_prng_makeseed (&seed))
{ {
static ddsrt_atomic_uint32_t counter = DDSRT_ATOMIC_UINT32_INIT (0);
/* Poor man's initialisation */ /* Poor man's initialisation */
DDSRT_STATIC_ASSERT (sizeof (seed.key) / sizeof (seed.key[0]) >= 3); DDSRT_STATIC_ASSERT (sizeof (seed.key) / sizeof (seed.key[0]) >= 4);
memset (&seed, 0, sizeof (seed)); memset (&seed, 0, sizeof (seed));
dds_time_t now = dds_time (); dds_time_t now = dds_time ();
seed.key[0] = (uint32_t) ddsrt_getpid (); seed.key[0] = (uint32_t) ddsrt_getpid ();
seed.key[1] = (uint32_t) ((uint64_t) now >> 32); seed.key[1] = (uint32_t) ((uint64_t) now >> 32);
seed.key[2] = (uint32_t) now; seed.key[2] = (uint32_t) now;
seed.key[3] = ddsrt_atomic_inc32_ov (&counter);
} }
ddsrt_prng_init (&default_prng, &seed); ddsrt_prng_init (&default_prng, &seed);
ddsrt_mutex_init (&default_prng_lock); ddsrt_mutex_init (&default_prng_lock);