On Tue, Jul 8, 2008 at 5:34 PM, Jeremy Pack <rostovpack@gmail.com> wrote:
Robert,
The first answer in my e-mail applies then - you can use the same factory_map for as many shared libraries as you'd like.
Other answers below:
Thanks for responding Jeremy.
I'm a little confused about your response, but perhaps that's because I don't know as much about shared libraries as I should. Basically, I'm assuming that the shared libraries must remain open in order to continue to use the factories.
Yes.
I'm not sure what you mean by closing the shared libraries I'm not using.
If you have no need to close the shared libraries (ie, you aren't getting low on RAM), then don't. You should only need that if you are loading many, many shared libraries. By default, they remain open.
I'm technically using the shared libraries every time I call factory::create(). However, once I concatenate the factory_map for each shared library, I do not use the factory_map any longer. I simply keep them stored in a boost::ptr_vector to maintain lifetime, and when I no longer need access to my concatenated list of factories, I simply destroy the ptr_vector of factory_map objects.
1 - The factory object is copyable - so you can just copy all of the std::map objects returned by factory_map::get into another map. You can then safely destroy the factory_map. 2 - You can just use a single factory_map anyway.
Say, for example, I load 3 shared libraries. As I add more shared
libraries, I am capable of creating more types, since each shared library provides a way for me to extend the capabilities of my factory (lets it create more types). In the case of having 3 shared libraries, the m_factories member would simply be 3 in size. I do not use the
m_factories member anywhere, it simply serves the purpose of
maintaining the lifetime of the shared libraries.
You don't need to do that to maintain the lifetime of the shared libraries. factory_map does not open or close shared libraries. Only the shared_library object does that. By default, shared libraries are left open forever (this is an option in the shared_library constructor). Feel free to delete factory_maps as soon as you have retrieved the factories that you need.
If you could explain in more detail what you mean by using the same
shared_library for multiple libraries, I would appreciate it. I figured there was a 1-to-1 mapping between factory_map and DLLs (on windows). ____________________________
Check out the example in libs/extension/examples/multiple_inheritance/main_mi.cpp.
It does something like this:
factory_map my_map; load_single_library(my_map, "first_library.extension", "extension_export"); load_single_library(my_map, "second_library.extension", "extension_export"); load_single_library(my_map, "third_library.extension", "extension_export");
Thus, it uses the same factory_map for every shared library.
If you only want the factories of a certain type (and delete the rest of the factory_map), you can then do the following:
factory_map *my_map; load_single_library(*my_map, "first_library.extension", "extension_export"); load_single_library(*my_map, "second_library.extension", "extension_export"); std::map<std::string, factory<computer> > factory_list; factory_list.swap(my_map->get<computer, std::string>()); delete my_map;
I think that in your case, this is what you want to do. Does that make more sense?
Yes, your explanation helps out tremendously. However, I noticed that load_single_library() simply deletes (by allowing it to fall out of scope) the shared_library object it creates as the function returns. Does this mean that it does not close the library when it is destroyed? So I will need to be responsible for calling shared_library::close() to release the DLL when I am done using it? I noticed also (you mentioned this) that there's an auto_close construction parameter in shared_library, however this value does not seem to get used anywhere. In fact, shared_library does not have a destructor that I can see. Does automatic unloading of shared libraries not work on destruction of shared_library objects even when setting auto_close to true? I'm assuming that by closing a shared_library, any factory objects created from that shared_library will not function anymore, since it won't have access to the classes it is creating. Thanks again for your continued help! PS: Do you have an online version of the trunk's documentation for Boost.Extension? I haven't been able to find this. Thank you.