chanegd wxTlsValue to be pointer-like instead of value-like which doesn't work for UDTs; use __thread keyword with mingw32 >= 4.3 too; use library-based thread-specific variables support in wxString cache now that it is fixed to work there; finally added a unit test for TLS stuff

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@55361 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/tls.h

@@ -10,18 +10,59 @@
     Macro to be used for thread-specific variables declarations.
 
     This macro can be used to define thread-specific variables of the specified
-    @a type. Such variables must be global or static. Example of use:
+    @a type. Such variables must be global or static and must be POD, i.e.
+    not have any constructors or destructor (even implicitly generated by the
+    compiler due to use of base classes or members which are not POD in a
+    struct).
+
+    Example of use:
     @code
     struct PerThreadData
     {
         ... data which will be different for every thread ...
     };
 
-    static wxTLS_TYPE(PerThreadData *) s_threadPtr;
+    static wxTLS_TYPE(PerThreadData) s_threadDataVar;
+    #define s_threadData (wxTLS_VALUE(s_threadDataVar))
+
+    ... use s_threadData as a variable of type PerThreadData ...
     @endcode
 
-    Currently only types of size less than size of a pointer are supported.
-    This limitation will be lifted in the future.
+    Notice that the use of the ugly wxTLS_VALUE() macro is unfortunately
+    required if you need to support platforms without native compiler support
+    for thread-specific variables. If you compile your code only on platforms
+    which do have such support (recent versions of GNU C++ compiler, Microsoft
+    Visual C++ and Sun C++ compiler are known to have it), you can avoid it and
+    use the variable directly.
  */
-#define wxTLS_TYPE(type)
+#define wxTLS_TYPE(type) compiler-dependent-implementation
 
+/**
+    Macro to access thread-specific variables.
+
+    This macro is used to hide the difference in implementation of
+    thread-specific variables under different platforms: they can be of type T
+    used in wxTLS_TYPE() if they are directly supported by the compiler or of
+    type emulating @c T @c *, i.e. a pointer to this type otherwise. This macro
+    always returns an expression of type @c T itself.
+
+    As shown in wxTLS_TYPE() example, you may want to @c #define a symbol
+    wrapping a thread-specific variable with this macro. And, as also explained
+    in wxTLS_TYPE() documentation, you may avoid using it entirely if you
+    target only recent compilers.
+
+    @see wxTLS_PTR()
+ */
+#define wxTLS_VALUE(var)
+
+/**
+    Macro to return address of a thread-specific variables.
+
+    This macro is similar to wxTLS_VALUE() except that it always returns a
+    pointer to the type of thread-specific variable.
+
+    Notice that this is not a constant expression even if the macro is defined
+    simply as @c &var -- the value returned is still different for every
+    thread.
+ */
+#define wxTLS_PTR(var)