id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
5341,Patch to improve shared library behavior with serialization,Aaron Barany <akb825@…>,Robert Ramey,"There are some issues that I have come across when using serialization with objects across shared libraries. I have made a patch that resolves the issues I have encountered, and will hopefully make serialization finally be friendly across multiple shared libraries.

The primary issue that I had was if there is a serializer created for an object, there can be some shared libraries that have a pointer serializer registered, and others that don't. This is actually quite common if you have the base class of an object declared in a separate library, since serializng a base class with base_object doesn't instanciate a pointer serializer.

Here is one case where this would prove to be an issue. Let's say the first time you wrote out a type it had no pointer serializer registered. It would write in the type info that tracking is not required and write out the object. Later, an object of the same type is written out from another shared library, but in this library a pointer serializer is registered. In this case, it will write out the object id, followed by the object itself. When that file is read in, it will read that the type has tracking disabled with the type information, and read the first instance just fine. However, on the second instance it still thinks that tracking is disabled, and will fail to read in the object id, even though it was written out.

I solved this issue by re-writing the archive serializer map to manage both pointer and non-pointer serializers. The map itself stores the non-pointer serializers in a multiset, so the serializers for all shared libraries are stored. When a iserializer/oserializer is constructed it is registered for that object type, and when it is destructed it is unregistered. pointer_iserializer/pointer_oserializer also register and unregister themselves with the map, but the behavior is different. What it will do is look at all non-pointer serializers of the proper type currently registered, and for any that don't have any pointer serializer registered for them it will use the pointer serializer currently being registered. When a pointer serializer is unregistered, it will search for an equivalent pointer serialier registered for another serializer for the same type (that was instanciated in a different library), or NULL if there is no such pointer serializer, and replace all instances of the pointer serializer being unregistered with that. Additionally, if a non-pointer serializer is being registered, it will look for an existing pointer serializer for that type to use. (it will quickly be replaced if there is a pointer serializer for that type instanciated in that library)

The effect at the end of the day is that for any given serializer, either all libraries or no libraries will have a pointer serializer registered for the corresponding non-pointer serializer. Since unregistration of pointer serializers tries to look for an equivalent to take its place, it should handle dynamic loading and unloading of libraries properly. Also, it should add no runtime cost during the actual usage of the serializers, only during the registration and unregistration.

The other issue I was having was I needed to create my own archive, but there was no way to export the archive serializer map symbols unless I put it in the boost serialization library, since it used the BOOST_ARCHIVE_OR_WARCHIVE_DECL() to generate the dllexport/dllimport declspecs. I changed it to use a technique described here. (http://support.microsoft.com/kb/168958) This allows customization for whether the symbols are imported and exported for each instantioation of archive_serializer_map. I also had to change all of the current archives to use this new method to register the archive serializer map.

I tried to keep consistent with your coding style and techniques. Since both this patch and the concrete to abstract patch I submitted earlier modify iserializer.hpp, I have also attached a combined patch that applies both.",Patches,reopened,To Be Determined,serialization,Boost 1.47.0,Showstopper,,serialization shared_libraries dlls,