<new>: SRWLOCK to protect the new handler instead of an indexed…

… `CRITICAL_SECTION` (#4407)

Co-authored-by: Stephan T. Lavavej <stl@nuwen.net>

stl/inc/yvals.h

@@ -310,7 +310,6 @@ _EMIT_STL_WARNING(STL4001, "/clr:pure is deprecated and will be REMOVED.");
 #endif // !defined(_CRTDATA2_IMPORT)
 
 #define _LOCK_LOCALE         0
-#define _LOCK_MALLOC         1
 #define _LOCK_STREAM         2
 #define _LOCK_DEBUG          3
 #define _LOCK_AT_THREAD_EXIT 4

stl/src/stdhndlr.cpp

@@ -3,11 +3,13 @@
 
 // set_new_handler
 
+#include <mutex>
 #include <new.h>
 #include <new>
 
 namespace {
     _STD new_handler _New_handler;
+    constinit _STD mutex _New_handler_mutex;
 
     int __cdecl _New_handler_interface(size_t) { // interface to existing Microsoft _callnewh mechanism
         _New_handler();
@@ -18,18 +20,16 @@ namespace {
 _STD_BEGIN
 
 _CRTIMP2 new_handler __cdecl set_new_handler(_In_opt_ new_handler pnew) noexcept { // remove current handler
-    _BEGIN_LOCK(_LOCK_MALLOC) // lock thread to ensure atomicity
+    lock_guard _Lock{_New_handler_mutex};
     new_handler pold = _New_handler;
     _New_handler     = pnew;
     _set_new_handler(pnew ? _New_handler_interface : nullptr);
     return pold;
-    _END_LOCK()
 }
 
 _CRTIMP2 new_handler __cdecl get_new_handler() noexcept { // get current new handler
-    _BEGIN_LOCK(_LOCK_MALLOC) // lock thread to ensure atomicity
+    lock_guard _Lock{_New_handler_mutex};
     return _New_handler;
-    _END_LOCK()
 }
 
 _STD_END