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Make genrand_int32 thread safe (#1797)

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The initialisation code is clearly meant to be run once but the volatile
flag did not guarantee that at all:

- Volatile does not mean atomic and loading the flag vs. other writes
  was not safe.
- Multiple threads could have loaded 0 and performed the initialisation
  resulting in write collisions.

Rely on std::call_once to provide the guarantee.

This issue was flagged by TSAN.

Signed-off-by: Kévin Petit <kpet@free.fr>
This commit is contained in:
Kévin Petit
2023-08-19 11:15:17 +01:00
committed by GitHub
parent df53e02a12
commit 0702f2ecee
1 changed files with 5 additions and 5 deletions
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10
test_common/harness/mt19937.cpp
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@@ -51,6 +51,7 @@
#include "harness/alloc.h"
#ifdef __SSE2__
#include <mutex>
#include <emmintrin.h>
#endif
@@ -107,7 +108,7 @@ cl_uint genrand_int32(MTdata d)
/* mag01[x] = x * MATRIX_A for x=0,1 */
static const cl_uint mag01[2] = { 0x0UL, MATRIX_A };
#ifdef __SSE2__
static volatile int init = 0;
static std::once_flag init_flag;
static union {
__m128i v;
cl_uint s[4];
@@ -123,8 +124,7 @@ cl_uint genrand_int32(MTdata d)
int kk;
#ifdef __SSE2__
if (0 == init)
{
auto init_fn = []() {
upper_mask.s[0] = upper_mask.s[1] = upper_mask.s[2] =
upper_mask.s[3] = UPPER_MASK;
lower_mask.s[0] = lower_mask.s[1] = lower_mask.s[2] =
@@ -134,8 +134,8 @@ cl_uint genrand_int32(MTdata d)
MATRIX_A;
c0.s[0] = c0.s[1] = c0.s[2] = c0.s[3] = (cl_uint)0x9d2c5680UL;
c1.s[0] = c1.s[1] = c1.s[2] = c1.s[3] = (cl_uint)0xefc60000UL;
init = 1;
}
};
std::call_once(init_flag, init_fn);
#endif
kk = 0;