Use hashmap for type mapping only on Windows

See comments in jlcxx.cpp for details

include/jlcxx/jlcxx_config.hpp

@@ -2,6 +2,7 @@
 #define JLCXX_CONFIG_HPP
 
 #ifdef _WIN32
+ #define JLCXX_USE_TYPE_MAP
  #ifdef JLCXX_EXPORTS
  #define JLCXX_API __declspec(dllexport)
  #else

include/jlcxx/module.hpp

@@ -1235,6 +1235,10 @@ class TypeWrapper
 
 using TypeWrapper1 = TypeWrapper<Parametric<TypeVar<1>>>;
 
+#ifdef JLCXX_USE_TYPE_MAP
+JLCXX_API std::shared_ptr<TypeWrapper1>& jlcxx_smartpointer_type(std::type_index idx);
+#endif
+
 template<typename ApplyT, typename... TypeLists> using combine_types = typename CombineTypes<ApplyT, TypeLists...>::type;
 
 template<typename T>

include/jlcxx/smart_pointers.hpp

@@ -189,8 +189,12 @@ struct SmartPtrMethods<PtrT<PointeeT, ExtraArgs...>, OtherPtrT>
 template<typename T>
 inline std::shared_ptr<TypeWrapper1>& stored_smartpointer_type()
 {
+#ifdef JLCXX_USE_TYPE_MAP
+ return jlcxx_smartpointer_type(typeid(T));
+#else
  static std::shared_ptr<TypeWrapper1> m_ptr;
  return m_ptr;
+#endif
 }
 
 template<typename T>

include/jlcxx/type_conversion.hpp

@@ -348,11 +348,51 @@ struct JLCXX_API CachedDatatype
  jl_datatype_t* m_dt = nullptr;
 };
 
+
+#ifdef JLCXX_USE_TYPE_MAP
+
+JLCXX_API CachedDatatype& jlcxx_type(std::type_index idx);
+JLCXX_API CachedDatatype& jlcxx_reftype(std::type_index idx);
+JLCXX_API CachedDatatype& jlcxx_constreftype(std::type_index idx);
+
+template<typename T>
+struct HashedCache
+{
+ static inline CachedDatatype& value()
+ {
+ return jlcxx_type(typeid(T));
+ }
+};
+
+template<typename T>
+struct HashedCache<T&>
+{
+ static inline CachedDatatype& value()
+ {
+ return jlcxx_reftype(typeid(T));
+ }
+};
+
+template<typename T>
+struct HashedCache<const T&>
+{
+ static inline CachedDatatype& value()
+ {
+ return jlcxx_constreftype(typeid(T));
+ }
+};
+
+#endif
+
 template<typename CppT>
-inline CachedDatatype& stored_type()
+CachedDatatype& stored_type()
 {
+#ifdef JLCXX_USE_TYPE_MAP
+ return HashedCache<CppT>::value();
+#else
  static CachedDatatype m_dt;
  return m_dt;
+#endif
 }
 
 template<typename T>

src/jlcxx.cpp

@@ -341,6 +341,50 @@ namespace detail
  };
 }
 
+#ifdef JLCXX_USE_TYPE_MAP
+
+// On windows, we can't store a mapping from the C++ type to the Julia type
+// in a static variable declared in a template function, since each DLL
+// will have its onw copy of that variable, making it impossible to share
+// type definitions between the CxxWrap base library and other libraries.
+// The workaround is to store the types in a map, but this is more fragile
+// because the guarantees on std::type_index are not very strong either
+// in the context of sharing information between shared libraries. This is
+// why we fall back to this approach only on Windows. Using type names is
+// also not a solution because types in anonymous namespaces will clash.
+// Refs:
+// https://stackoverflow.com/questions/398069/static-member-variable-in-template-with-multiple-dlls
+// https://developercommunity.visualstudio.com/t/template-static-members-and-multiple-definitions-a/1202888
+// https://github.com/pybind/pybind11/pull/4319
+// https://bugs.llvm.org/show_bug.cgi?id=33542
+// https://github.com/pybind/pybind11/issues/3289
+
+JLCXX_API CachedDatatype& jlcxx_type(std::type_index idx)
+{
+ static std::unordered_map<std::type_index, CachedDatatype> m_map;
+ return m_map.insert(std::make_pair(idx,CachedDatatype())).first->second;
+}
+
+JLCXX_API CachedDatatype& jlcxx_reftype(std::type_index idx)
+{
+ static std::unordered_map<std::type_index, CachedDatatype> m_map;
+ return m_map.insert(std::make_pair(idx,CachedDatatype())).first->second;
+}
+
+JLCXX_API CachedDatatype& jlcxx_constreftype(std::type_index idx)
+{
+ static std::unordered_map<std::type_index, CachedDatatype> m_map;
+ return m_map.insert(std::make_pair(idx,CachedDatatype())).first->second;
+}
+
+JLCXX_API std::shared_ptr<TypeWrapper1>& jlcxx_smartpointer_type(std::type_index idx)
+{
+ static std::unordered_map<std::type_index, std::shared_ptr<TypeWrapper1>> m_map;
+ return m_map.insert(std::make_pair(idx, nullptr)).first->second;
+}
+
+#endif
+
 JLCXX_API void register_core_types()
 {
  if(jl_base_module == nullptr)