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-rw-r--r--indra/llcommon/llrand.cpp20
1 files changed, 18 insertions, 2 deletions
diff --git a/indra/llcommon/llrand.cpp b/indra/llcommon/llrand.cpp
index 33afc50cf7..20e25177f0 100644
--- a/indra/llcommon/llrand.cpp
+++ b/indra/llcommon/llrand.cpp
@@ -28,6 +28,7 @@
#include "llrand.h"
#include "lluuid.h"
+#include "mutex.h"
/**
* Through analysis, we have decided that we want to take values which
@@ -58,8 +59,17 @@
* to restore uniform distribution.
*/
+static std::mutex gRandomGeneratorMutex;
static LLRandLagFib2281 gRandomGenerator(LLUUID::getRandomSeed());
+inline F64 ll_internal_random_unclamped()
+{
+ // gRandomGenerator is a stateful static object, which is therefore not
+ // inherently thread-safe. Lock it before use.
+ std::unique_lock lk(gRandomGeneratorMutex);
+ return gRandomGenerator();
+}
+
// no default implementation, only specific F64 and F32 specializations
template <typename REAL>
inline REAL ll_internal_random();
@@ -71,7 +81,7 @@ inline F64 ll_internal_random<F64>()
// CPUs (or at least multi-threaded processes) seem to
// occasionally give an obviously incorrect random number -- like
// 5^15 or something. Sooooo, clamp it as described above.
- F64 rv = gRandomGenerator();
+ F64 rv{ ll_internal_random_unclamped() };
if(!((rv >= 0.0) && (rv < 1.0))) return fmod(rv, 1.0);
return rv;
}
@@ -79,7 +89,13 @@ inline F64 ll_internal_random<F64>()
template <>
inline F32 ll_internal_random<F32>()
{
- return F32(ll_internal_random<F64>());
+ // *HACK: clamp the result as described above.
+ // Per Monty, it's important to clamp using the correct fmodf() rather
+ // than expanding to F64 for fmod() and then truncating back to F32. Prior
+ // to this change, we were getting sporadic ll_frand() == 1.0 results.
+ F32 rv{ ll_internal_random_unclamped() };
+ if(!((rv >= 0.0) && (rv < 1.0))) return fmodf(rv, 1.0f);
+ return rv;
}
/*------------------------------ F64 aliases -------------------------------*/