cache the result of wxGetOsVersion() (heavily modified patch 1783198)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@48621 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/utils.cpp

@@ -1199,32 +1199,64 @@ bool wxIsPlatform64Bit()
 
 wxOperatingSystemId wxGetOsVersion(int *verMaj, int *verMin)
 {
+    static struct
+    {
+        // this may be false, true or -1 if we tried to initialize but failed
+        int initialized;
+
+        wxOperatingSystemId os;
+
+        int verMaj,
+            verMin;
+    } s_version;
+
+    // query the OS info only once as it's not supposed to change
+    if ( !s_version.initialized )
+    {
         OSVERSIONINFO info;
         wxZeroMemory(info);
-
+        info.dwOSVersionInfoSize = sizeof(info);
-    info.dwOSVersionInfoSize = sizeof(OSVERSIONINFO);
         if ( ::GetVersionEx(&info) )
         {
-        if (verMaj) *verMaj = info.dwMajorVersion;
+            s_version.initialized = true;
-        if (verMin) *verMin = info.dwMinorVersion;
-    }
 
-#if defined( __WXWINCE__ )
+#if defined(__WXWINCE__)
-    return wxOS_WINDOWS_CE;
+            s_version.os = wxOS_WINDOWS_CE;
-#elif defined( __WXMICROWIN__ )
+#elif defined(__WXMICROWIN__)
-    return wxOS_WINDOWS_MICRO;
+            s_version.os = wxOS_WINDOWS_MICRO;
-#else
+#else // "normal" desktop Windows system, use run-time detection
             switch ( info.dwPlatformId )
             {
                 case VER_PLATFORM_WIN32_NT:
-        return wxOS_WINDOWS_NT;
+                    s_version.os = wxOS_WINDOWS_NT;
+                    break;
 
                 case VER_PLATFORM_WIN32_WINDOWS:
-        return wxOS_WINDOWS_9X;
+                    s_version.os = wxOS_WINDOWS_9X;
+                    break;
+            }
+#endif // Windows versions
+
+            s_version.verMaj = info.dwMajorVersion;
+            s_version.verMin = info.dwMinorVersion;
+        }
+        else // GetVersionEx() failed
+        {
+            s_version.initialized = -1;
+        }
     }
 
-    return wxOS_UNKNOWN;
+    if ( s_version.initialized == 1 )
-#endif
+    {
+        if ( verMaj )
+            *verMaj = s_version.verMaj;
+        if ( verMin )
+            *verMin = s_version.verMin;
+    }
+
+    // this works even if we were not initialized successfully as the initial
+    // values of this field is 0 which is wxOS_UNKNOWN and exactly what we need
+    return s_version.os;
 }
 
 wxWinVersion wxGetWinVersion()