I want to extend lifetime of the boost::log::core for termination process.
I know that this is not recommended in the documentation. But I tried to use Schwarz counter for core to keep it until last destructor of global variable used it.
Core uses the shared pointer with Meyer's singleton. is it possible to implement Schwarz counter or nifty initialization core ?
The core::get() method returns a shared_ptr to the core, which is what implements the Schwarz counter. You can call this method during the normal operation of the program (i.e. while main() is executing) and save that pointer in your data structures that are guaranteed to be present during termination. While the shared_ptr exists, you can access the core through that pointer (but not necessarily through core::get()).
Note that all loggers provided by the library also save the pointer to the core internally. For example, if you're performing termination in an object destructor, make a logger a member of that object and you will be able to emit simple log records during the destruction.
Note that the core is not the only singleton the library maintains, and other singletons are not protected from destruction by this method. For example, you cannot use global loggers during program termination.