F.A.Q.

Question: Is Boost.DLL thread-safe?
- Answer: Some platforms allow concurrent calls to dlopen like functions. For those platforms Boost.DLL is safe in the manner as all the C++ Standard Library containers are: it is safe to use different instances of shared_library from different threads even if all the instances loaded the same library. On other platforms it is not safe to concurrently call any of the functions from Boost.DLL (even a shared_library::location() call triggers a race condition). See Limitations, Thread safe library loading.

Question: Why on Linux symbols from one plugin are seen in another? Can't get symbol with same name from right plugin!
- Answer: You've run into the symbol shadowing problem. Compile your plugins with "-fvisibility=hidden" flag and take a look to the Tutorial section.

Question: How Unicode (Windows) is handled?
- Answer: Boost.DLL supports Unicode, so that you could provide Unicode paths to it.

Question: Can I open an executable file?
- Answer: Yes, you can. Symbols need be exported using in the executable using BOOST_SYMBOL_EXPORT or BOOST_DLL_ALIAS. You can call shared_library(program_location()) to load yourself. Refer to the Tutorial section for more info. You can also query executables, just provide a path to the executable to library_info class.

Question: What if I specify wrong type in shared_library::get<T> or import<T>?
- Answer: Usually you'll end up with Segmentation Fault. However it is safe to make types more strict, for example making const int from an int will not harm.

Question: Does your library guarantee ABI stability of methods?
- Answer: Library only guarantees that alias names created using the BOOST_DLL_ALIAS macros will not change with the change of compiler or platform. You must take care of functions ABI and API stability by your own.

Question: Are there any function signature restrictions for the exported/imported functions?
- Answer: No. You may import/export functions with any signature and any return parameter.

Question: I have 2 plugins that use same shared library. Would be the shared library loaded twice?
- Answer: No. Pugins will share the shared library instance.

Question: I have 2 plugins each of them must work with it's own version of libsome_library shared library. How to achieve that?
- Answer: Avoid such situations by statically linking in the libsome_library into each plugin and loading plugins with load_mode::rtld_deepbind.

Question: How to load a shared object from memory??
- Answer: All existing OS avoid loading shared libraries directly from userspace memory, so you'll find no syscall for such case. Currently Boost.DLL provides no means for honest loading shared objects from memory. This requires reimplementing dynamic linker logic in userspace for all the platforms, which is a huge amount of work and very error-prone. However working patches are welcomed!

Workaround would be to write plugin into a temporary file in RAM and load plugin from it:

#include <boost/filesystem.hpp>
#include <boost/dll.hpp>
using namespace boost;

dll:shared_library load_from_memory(unsigned char* data, std::size_t size, const filesystem::path& tmp_plugin_path = filesystem::unique_path() / "libplugin.so") {
    const filesystem::path plugin_location = filesystem::temp_directory_path() / tmp_plugin_path;
    filesystem::create_directories(plugin_location.parent_path());
    filesystem::ofstream ofs(plugin_location, std::ios::out|std::ios::bin|std::ios::trunc);
    ofs.write(data, size);

    return dll::shared_library(plugin_location);
}

But there's no guarantee that filesystem::temp_directory_path() will actually write to RAM, that's very platform dependent.

Question: Can I use function pointer type (like void(*)()) instead of function type (like void()) to import function?
- Answer: No you can't because the meaning of importing a function pointer is different:
  - lib.get<void()>("func") imports a function void func()
  - lib.get<void(*)()>("func_var") imports a variable that stores a pointer to the function auto func_var = &func

Question: I have found a bug, how do I notify?
- Answer: Create an issue at GitHub with a detailed description.

Boost C++ Libraries

F.A.Q.