5 files changed, 27 insertions, 30 deletions
diff --git a/indra/llcommon/classic_callback.h b/indra/llcommon/classic_callback.h
index 1ad6dbc58f..009c25d67c 100644
--- a/indra/llcommon/classic_callback.h
+++ b/indra/llcommon/classic_callback.h
@@ -119,11 +119,11 @@ public:
      * ClassicCallback must not itself be copied or moved! Once you've passed
      * get_userdata() to some API, this object MUST remain at that address.
      */
-    // However, we can't yet count on C++17 Class Template Argument Deduction,
-    // which means makeClassicCallback() is still useful, which means we MUST
-    // be able to return one to construct into caller's instance (move ctor).
-    // Possible defense: bool 'referenced' data member set by get_userdata(),
-    // with an llassert_always(! referenced) check in the move constructor.
+    // However, makeClassicCallback() is useful for deducing the CALLABLE
+    // type, which means we MUST be able to return one to construct into
+    // caller's instance (move ctor). Possible defense: bool 'referenced' data
+    // member set by get_userdata(), with an llassert_always(! referenced)
+    // check in the move constructor.
     ClassicCallback(ClassicCallback const&) = delete;
     ClassicCallback(ClassicCallback&&) = default; // delete;
     ClassicCallback& operator=(ClassicCallback const&) = delete;
diff --git a/indra/llcommon/llrand.cpp b/indra/llcommon/llrand.cpp
index 33afc50cf7..e4065e23bf 100644
--- a/indra/llcommon/llrand.cpp
+++ b/indra/llcommon/llrand.cpp
@@ -58,7 +58,9 @@
  * to restore uniform distribution.
  */
 
-static LLRandLagFib2281 gRandomGenerator(LLUUID::getRandomSeed());
+// gRandomGenerator is a stateful static object, which is therefore not
+// inherently thread-safe.
+static thread_local LLRandLagFib2281 gRandomGenerator(LLUUID::getRandomSeed());
 
 // no default implementation, only specific F64 and F32 specializations
 template <typename REAL>
@@ -71,7 +73,7 @@ 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{ gRandomGenerator() };
 	if(!((rv >= 0.0) && (rv < 1.0))) return fmod(rv, 1.0);
 	return rv;
 }
@@ -79,7 +81,13 @@ 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{ narrow(gRandomGenerator()) };
+	if(!((rv >= 0.0f) && (rv < 1.0f))) return fmodf(rv, 1.0f);
+	return rv;
 }
 
 /*------------------------------ F64 aliases -------------------------------*/
diff --git a/indra/llcommon/llthread.cpp b/indra/llcommon/llthread.cpp
index 4eaa05c335..cd4975d9d3 100644
--- a/indra/llcommon/llthread.cpp
+++ b/indra/llcommon/llthread.cpp
@@ -113,15 +113,16 @@ LL_COMMON_API bool on_main_thread()
     return (LLThread::currentID() == main_thread());
 }
 
-LL_COMMON_API void assert_main_thread()
+LL_COMMON_API bool assert_main_thread()
 {
     auto curr = LLThread::currentID();
     auto main = main_thread();
-    if (curr != main)
-    {
-        LL_WARNS() << "Illegal execution from thread id " << curr
-            << " outside main thread " << main << LL_ENDL;
-    }
+    if (curr == main)
+        return true;
+
+    LL_WARNS() << "Illegal execution from thread id " << curr
+               << " outside main thread " << main << LL_ENDL;
+    return false;
 }
 
 // this function has become moot
diff --git a/indra/llcommon/llthread.h b/indra/llcommon/llthread.h
index 50202631e7..9f1c589fcd 100644
--- a/indra/llcommon/llthread.h
+++ b/indra/llcommon/llthread.h
@@ -152,7 +152,7 @@ public:
 
 //============================================================================
 
-extern LL_COMMON_API void assert_main_thread();
+extern LL_COMMON_API bool assert_main_thread();
 extern LL_COMMON_API bool on_main_thread();
 
 #endif // LL_LLTHREAD_H
diff --git a/indra/llcommon/stdtypes.h b/indra/llcommon/stdtypes.h
index 0b43d7ad4b..3aba9dda00 100644
--- a/indra/llcommon/stdtypes.h
+++ b/indra/llcommon/stdtypes.h
@@ -156,18 +156,15 @@ typedef int intptr_t;
  * type.
  */
 // narrow_holder is a struct that accepts the passed value as its original
-// type and provides templated conversion functions to other types. Once we're
-// building with compilers that support Class Template Argument Deduction, we
-// can rename this class template 'narrow' and eliminate the narrow() factory
-// function below.
+// type and provides templated conversion functions to other types.
 template <typename FROM>
-class narrow_holder
+class narrow
 {
 private:
     FROM mValue;
 
 public:
-    narrow_holder(FROM value): mValue(value) {}
+    narrow(FROM value): mValue(value) {}
 
     /*---------------------- Narrowing unsigned to signed ----------------------*/
     template <typename TO,
@@ -207,13 +204,4 @@ public:
     }
 };
 
-/// narrow() factory function returns a narrow_holder<FROM>(), which can be
-/// implicitly converted to the target type.
-template <typename FROM>
-inline
-narrow_holder<FROM> narrow(FROM value)
-{
-    return { value };
-}
-
 #endif