Fix static initialization order for UserFormatRegister map

A std::map is in an invalid state when just zero-initialized, and needs
to be initialized by its constructor. As this initilization may be done
after the first call to Register, a crash will typically happen.

To fix this wrap all accesses to the map with a Meyers Singleton. Also
remove the extra Array - most accesses are using the key, and the few
format list iterations all sort the result afterwards anyway.

Fixes NGSolve#201.

libsrc/interface/writeuser.cpp

@@ -16,19 +16,38 @@
 
 namespace netgen
 {
-  extern MeshingParameters mparam;
+  std::map<std::string, UserFormatRegister::UserFormatEntry>& UserFormatRegister::getFormats()
+  {
+      static std::map<std::string, UserFormatRegister::UserFormatEntry> formats = {};
+      return formats;
+  }
 
-  Array<UserFormatRegister::UserFormatEntry> UserFormatRegister::entries;
-  std::map<string, int> UserFormatRegister::format_to_entry_index;
+  void UserFormatRegister::Register(UserFormatRegister::UserFormatEntry && entry)
+  {
+      getFormats()[entry.format] = std::move(entry);
+  }
+
+  const bool UserFormatRegister::HaveFormat(string format)
+  {
+      const auto formats = getFormats();
+      return formats.find(format) != formats.end();
+  }
+
+  const UserFormatRegister::UserFormatEntry & UserFormatRegister::Get(string format)
+  {
+      return getFormats()[format];
+  }
+
+  extern MeshingParameters mparam;
 
   void RegisterUserFormats (NgArray<const char*> & names,
 			    NgArray<const char*> & extensions)
 
 {
-  for (const auto & entry : UserFormatRegister::entries)
+  for (const auto & entry : UserFormatRegister::getFormats())
     {
-      names.Append (entry.format.c_str());
-      extensions.Append (entry.extensions[0].c_str());
+      names.Append (entry.second.format.c_str());
+      extensions.Append (entry.second.extensions[0].c_str());
     }
 }
 

libsrc/interface/writeuser.hpp

@@ -28,32 +28,23 @@ struct UserFormatRegister {
     optional<FRead> read;
     optional<FWrite> write;
   };
-  DLL_HEADER static Array<UserFormatEntry> entries;
-  DLL_HEADER static std::map<string, int> format_to_entry_index;
+  static void Register(UserFormatEntry && entry);
 
-  static void Register(UserFormatEntry && entry) {
-    format_to_entry_index[entry.format] = entries.Size();
-    entries.Append( std::move(entry) );
-  }
-
-  static const bool HaveFormat(string format) {
-    return format_to_entry_index.count(format) > 0;
-  }
-  static const UserFormatEntry & Get(string format) {
-    return entries[format_to_entry_index[format]];
-  }
+  static const bool HaveFormat(string format);
+  DLL_HEADER static const UserFormatEntry & Get(string format);
 
   template<typename TFunc>
   static void IterateFormats(TFunc func, bool need_read=false, bool need_write=false) {
     Array<string> import_formats;
-    for(const auto & e: entries)
-    if((!need_read || e.read) && (!need_write || e.write))
-      import_formats.Append(e.format);
+    for(const auto & e: getFormats())
+    if((!need_read || e.second.read) && (!need_write || e.second.write))
+      import_formats.Append(e.second.format);
     QuickSort(import_formats);
     for(auto format : import_formats)
-      func(entries[format_to_entry_index[format]]);
+      func(Get(format));
   }
 
+  DLL_HEADER static std::map<std::string, UserFormatEntry>& getFormats();
 };
 
 struct RegisterUserFormat {

libsrc/meshing/python_mesh.cpp

@@ -700,14 +700,16 @@ DLL_HEADER void ExportNetgenMeshing(py::module &m)
 
   string export_docu = "Export mesh to other file format. Supported formats are:\n";
   Array<string> export_formats;
-  for(auto & e : UserFormatRegister::entries)
+  for(auto & kv : UserFormatRegister::getFormats()) {
+    const auto e = kv.second;
     if(e.write) {
       string s = '\t'+e.format+"\t("+e.extensions[0];
       for(auto & ext : e.extensions.Range(1, e.extensions.Size()))
         s += ", "+ext;
       s += ")\n";
       export_formats.Append(s);
     }
+  }
   QuickSort(export_formats);
   for(const auto & s : export_formats)
     export_docu += s;